U.S. patent application number 11/378619 was filed with the patent office on 2007-09-20 for use of pi-conjugated organoboron polymers in thin-film organic polymer electronic devices.
Invention is credited to Silvia DeVito Luebben, Shawn A. Sapp.
Application Number | 20070215864 11/378619 |
Document ID | / |
Family ID | 38516850 |
Filed Date | 2007-09-20 |
United States Patent
Application |
20070215864 |
Kind Code |
A1 |
Luebben; Silvia DeVito ; et
al. |
September 20, 2007 |
Use of pi-conjugated organoboron polymers in thin-film organic
polymer electronic devices
Abstract
Pi-conjugated organoboron polymers for use in thin-film organic
polymer electronic devices. The polymers contain aromatic and or
unsaturated repeat units and boron atoms. The vacant p-orbital of
the boron atoms conjugate with the pi-conjugated orbital system of
the aromatic or unsaturated monomer units extending the
pi-conjugation length of the polymer across the boron atoms. The
pi-conjugated organoboron polymers are electron-deficient and,
therefore, exhibit n-type semiconducting properties,
photoluminescence, and electroluminescence. The invention provides
thin-film organic polymer electronic devices, such as organic
photovoltaic cells (OPVs), organic diodes, organic photodiodes,
organic thin-film transistors (TFTs), organic field-effect
transistors (OFETs), printable or flexible electronics, such as
radio-frequency identification (RFID) tags, electronic papers, and
printed circuit elements, organic light-emitting diodes (OLEDs),
polymer light-emitting diodes (PLEDs), and energy storage devices
employing the pi-conjugated organoboron polymers. In OLED and PLED
applications these materials are used as the electron transport
layer (ETL) to improve device efficiency. The polymers which
exhibit photo- and electroluminescence are also useful as
light-emitting material in PLEDs.
Inventors: |
Luebben; Silvia DeVito;
(Golden, CO) ; Sapp; Shawn A.; (Westminster,
CO) |
Correspondence
Address: |
GREENLEE WINNER AND SULLIVAN P C
4875 PEARL EAST CIRCLE
SUITE 200
BOULDER
CO
80301
US
|
Family ID: |
38516850 |
Appl. No.: |
11/378619 |
Filed: |
March 17, 2006 |
Current U.S.
Class: |
257/40 ;
257/E51.028; 257/E51.036; 313/504; 313/506; 428/690; 428/917;
528/377; 528/394; 528/4; 528/423 |
Current CPC
Class: |
H01L 51/008 20130101;
C09K 11/06 20130101; C09K 2211/1425 20130101; H01L 51/0545
20130101; H01L 51/004 20130101; C08G 79/08 20130101; H01L 51/0043
20130101; C09K 2211/1466 20130101; H01L 51/0039 20130101; H01L
51/0541 20130101; H01L 51/4246 20130101; C08G 2261/94 20130101;
C09K 2211/1475 20130101; H01L 51/0035 20130101; Y10S 428/917
20130101; H05B 33/14 20130101; C09K 2211/1433 20130101; C09K
2211/1483 20130101; H01L 51/4253 20130101; H01L 51/5012 20130101;
Y02E 10/549 20130101 |
Class at
Publication: |
257/040 ;
257/E51.028; 257/E51.036; 528/004; 528/394; 528/377; 528/423;
313/504; 313/506; 428/690; 428/917 |
International
Class: |
H01L 51/00 20060101
H01L051/00; H01L 51/54 20060101 H01L051/54; C08G 79/08 20060101
C08G079/08 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] This invention was made, at least in part, with funding from
National Science Foundation contract DMI-0319320. The United States
government has certain rights in the invention.
Claims
1. A thin film, organic polymer electronic device which comprises
at least one active layer containing a first thin film of a
pi-conjugated organoboron polymer and at least two electrodes in
contact with the active layer.
2. The device of claim 1 wherein the first thin film of the
pi-conjugated organoboron polymer is 100 angstroms to 10000
angstroms in thickness.
3. The device of claim 1 wherein the first thin film of the
pi-conjugated organoboron polymer is 100 angstroms to 3000
angstroms in thickness.
4. The device of claim 3 that exhibits current rectification or
diode-like properties.
5. The device of claim 4 wherein the first thin film of a
pi-conjugated organoboron polymer emits light under a voltage
bias.
6. The device of claim 4 wherein the active layer of the device
contains a second thin film containing a light-emitting polymer
that is not a pi-conjugated organoboron polymer.
7. The device of claim 4 wherein the device contains a second thin
film containing a light-emitting non-polymeric molecule.
8. The device of claim 1 wherein the first thin film comprises a
pi-conjugated organoboron polymer blended with a light-emitting
non-polymeric molecule.
9. The device of claim 1 wherein the first thin film comprises a
pi-conjugated organoboron polymer blended with an organic or
inorganic conducting or semiconducting material.
10. The device of claim 1 wherein the first thin film comprises a
p-type conducting or semiconducting polymer blended with a
pi-conjugated organoboron polymer.
11. The device of claim 1 wherein the first thin film comprises a
p-type conducting or semiconducting molecule blended with a
pi-conjugated organoboron polymer.
12. The device of claim 1 wherein the first thin film comprises
inorganic p-type semiconducting particles mixed with a
pi-conjugated organoboron polymer.
13. The device of claim 12 wherein the inorganic p-type
semiconducting particles have at least one dimension less than 1000
angstroms.
14. The device of claim 1 wherein the active layer comprises a
second thin film of a dielectric material wherein the second thin
film is in contact with one or more additional electrodes.
15. The device of claim 1 wherein the pi-conjugated organoboron
polymer has any of the structures: ##STR13## wherein each R,
independent of other R's in the repeating unit, and R.sub.1,
independent of any R's, can be hydrogen, deuterium, a halogen atom,
or an organic radical, Ar represents a divalent aromatic radical
which may optionally carry one or more other organic radical
groups, substituent groups, and/or functional groups described
herein and "n", "m" and "p" are integers representing the number of
indicated moieties in a repeating unit or the average degree of
polymerization of the polymer.
16. The device of claim 1 wherein the pi-conjugated organoboron
polymer has the structure: ##STR14## where: Ar is a divalent
radical resulting from the removal of two hydrogen atoms from
benzene, naphthalene, diphenyl, pyridine, pyrimidine, triazine,
pyrrole, N-alkylpyrroles, N-substituted pyrroles, 3-substituted
pyrroles, furan, tetrazole, indole, purine, oxadiazole,
quinoxaline, phenazine, N,N'-dialkylphenazines, phenothiazine,
N-alkylphenothiazines, carbazole, N-alkylcarbazoles, thiophene,
3-alkylthiophenes, 3-substituted thiophenes, 3,4-disubstituted
thiophenes, thienothiophene, substituted thienothiophenes,
bithiophene, terthiophene, quaterthiophene, dialkyloxybenzenes,
oxadiazole, fluorene, 9,9-dialkylfluorenes and their substituted
derivatives; R.sub.1 is any aliphatic or aromatic radical; and n is
an integer.
17. The device of claim 1 wherein the pi-conjugated organoboron
polymer has the structure: ##STR15## where each R, independent of
other R's in the repeating unit, and R.sub.1, independent of any
R's, can be hydrogen, deuterium, a halogen atom, or an organic
radical, and n, m and p are integer numbers indicating the average
degree of polymerization of the polymer or the number of repeat
units.
18. An organoboron polymer having the structure: ##STR16## where Ar
is a divalent radical resulting from the removal of two hydrogen
atoms from, pyridine, pyrimidine, triazine, pyrrole,
N-alkylpyrroles, N-substituted pyrroles, 3-substituted pyrroles,
furan, tetrazole, indole, purine, oxadiazole,
1,5-diphenyl-oxadiazole, quinoxaline, phenazine,
N,N'-dialkylphenazines, phenothiazine, N-alkylphenothiazines,
carbazole, N-alkylcarbazoles, 3,4-disubstituted thiophenes,
thienothiophene, substituted thienothiophenes, oxazole, fluorene,
9,9-dialkylfluorenes and their substituted derivatives; R.sub.1,
independent of other R.sub.1 in the repeating unit are hydrogens,
deuterium atoms, halogen atoms, linear or branched alkyl radicals
which can be optionally substituted with one or more non-hydrogen
substituents or functional groups; and n is an integer representing
the average degree of polymerization of the polymer.
19. The polymer of claim 18 wherein Ar is selected from the group
consisting of fluorenes, substituted fluorenes and 9,9,
dialkylfluorenes.
20. The polymer of claim 18 wherein Ar is selected from the group
consisting of ##STR17## wherein R.sub.2 and R.sub.3, independently
of each other, are hydrogens, deuterium atoms, halogen atoms, or
linear or branched alkyl radicals, which can be optionally
substituted with one or more non-hydrogen substituents or
functional groups or R.sub.2 represents an organic group that links
two ring positions wherein R.sub.2 can represent multiple
independent substituents or functional groups on the rings and m is
an integer ranging from 1 to 6.
21. The polymer of claims 20 wherein m is an integer from 1 to
3.
22. The polymer of claims 20 wherein Ar is ##STR18##
23. The polymer of claim 20 wherein R.sub.2 and R.sub.3 are
hydrogens, deuteriums or alkyl groups.
24. An organoboron polymer having structure: ##STR19## where each
R, R.sub.1, R.sub.2 independent of each other is a hydrogen,
deuterium, a halogen atom, or an organic radical, and n, m and p
are integer numbers indicating the average degree of polymerization
of the polymer or the number of repeat units.
25. An organoboron polymer having the structure: ##STR20## where
R.sub.4 is an optionally substituted saturated or unsaturated
organic radical or an aromatic radical; R, independent of other R's
in the repeating unit, is hydrogen, deuterium, a halogen atom, a
silyl radical, or an organic radical and n is an integer
representing the average degree of polymerization of the
polymer.
26. The polymer of claim 22 wherein each R is hydrogen or
deuterium.
Description
FIELD OF THE INVENTION
[0002] This invention relates to the use of pi-conjugated (or
.pi.-conjugated) organoboron polymers in thin film electronic
devices and methods for the fabrication of such devices.
BACKGROUND OF THE INVENTION
[0003] The specific functions of many electronic components and
devices arise from the unique interactions existing between p-type
and n-type conducting and semiconducting materials. Until a few
years ago, inorganic conductors and semiconductors entirely
dominated the electronic industry. In recent years there has been a
major worldwide research effort to develop conducting and
semiconducting organic compounds and polymers, and to use them to
fabricate plastic electronic devices, such as organic thin film
transistors (TFTs), organic light emitting diodes (OLEDs),
printable circuits, organic supercapacitors and organic
photovoltaic devices. Plastic electronic components offer several
potential advantages over traditional devices made of inorganic
materials; they are flexible and can be manufactured by inexpensive
ink-jet printing or roll-to-roll coating technologies.
[0004] Intrinsically conducting polymers (ICPs) are polymers with
extended .pi. conjugation along the molecular backbone, and their
conductivity can be changed by several orders of magnitude by
doping. P-doping is the partial oxidation of the polymer by a
chemical oxidant or an electrode which causes depopulation of the
bonding .pi. orbital (HOMO) with the injection of "holes". N-doping
is the partial reduction of the polymer by a chemical reducing
agent or electrode with the injection of electrons in the
antibonding .pi. system (LUMO, MacDiarmid A., Angew. Chem. Int.
Ed., 40, 2581-2590, 2001). The doping process incorporates charge
carriers (either electrons or holes) into the polymer backbone, and
as a result the polymer becomes electrically conducting to a level
that is commensurate with its doping level.
[0005] An equally important class of electronic polymers is the
conjugated semiconducting polymers. These polymers, like ICPs, are
able to support the injection of p-type or n-type charge carriers;
however the charge carriers are often few in number and are
transient species that ultimately decay or are transferred to a
different material. Some ICPs function as semiconducting polymers
in their undoped state, however other ICPs are not stable in their
semiconducting state. Electrical conductivity and work function are
the key parameters for characterizing ICPs, while charge carrier
density and mobility, and energy levels are the key parameters for
characterizing semiconducting polymers. One special class of
semiconducting polymers is the group of light emitting polymers.
These polymers are also able to support the injection and transport
of both positive and negative charges (although one carrier is
often preferred). When holes and electrons recombine within the
electroluminescent material, a neutral excited species (termed an
exciton) forms that decays to the ground state, liberating energy
in the form of light (Salaneck, W. R. et al., Nature,
397,121-128,1999).
[0006] Thus, certain pi-conjugated polymers are well known to
possess semiconducting properties which are due to the formation of
interconnected molecular orbitals along the pi-bonding and
pi-antibonding structure of the conjugated backbone. Charges that
are introduced onto such polymer chains (either by addition or
removal of an electron) are free to travel over a certain distance
along the polymer chain giving rise to semiconducting properties.
The number of charges that can be injected, the ease of introducing
charges, the distance that a charge can travel (mobility), and the
type of charge (positive holes or negative electrons) that is more
favorable depends upon the electronic properties of the polymer. By
careful design of the structure of the polymer, a structure that
favors electrons (called an n-type semiconductor) or holes (called
a p-type semiconductor) as the dominant form of charge carrier can
be selected. This is done through introduction into the polymer of
selected atoms, organic groups and/or substituent groups on the
basis of their electron-donating or electron-withdrawing
properties. Appropriate selections of atoms or groups for
introduction into the polymer structure lead to a conjugated
polymer structure that is either electron-rich or
electron-deficient. Electron-rich polymer structures have p-type
semiconducting properties and electron-deficient polymer structures
have n-type semiconducting properties.
[0007] Most pi-conjugated hydrocarbon polymers such as
polyacetylene, poly(phenylenevinylene), poly(paraphenylene),
polyfluorenes and their derivatives readily support the injection
of both electrons and holes (the respective n-type and p-type
charge carriers). In fact, theoretical calculations show that for
certain hydrocarbon conjugated polymers such as poly(paraphenylene)
there is a perfect electron-hole symmetry [i.e. the frontier
orbitals of positively and negatively charged carriers are fully
symmetrical], indicating that electron and hole conduction are
equally favorable processes (Kertesz, M. in Handbook of Organic
Conductive Molecules and Polymers, Vol. 4, Ed. Hari Singh Nalwa, J.
Wiley & Sons, Chichester, UK, p. 163, 1997). This symmetry can
be broken by introducing atoms other than carbon (heteroatoms),
organic groups and/or substituent groups that are either
electron-rich or electron-deficient, thus favoring either the
injection of holes or electrons, respectively. It is generally
easier to design electron-rich conjugated polymers than
electron-deficient conjugated polymers. An electron-rich polymer
can be created by appropriate introduction of an electro-negative
heteroatom such as sulfur, nitrogen or oxygen into the conjugated
polymer. A variety of chemistries are available in the art for
introducing electro-negative heteroatoms into such polymers. As a
result a large number of p-type conducting polymers have been
developed and characterized over the past two decades. Furthermore,
many p-type conducting and semiconducting polymers have been used
in commercial devices and are successfully competing with
conventional inorganic semiconductors and conductors.
[0008] In contrast, it is more difficult to design
electron-deficient conjugated polymer systems. Most of the polymers
currently used as n-type semiconductors are hydrocarbon-based
polymers [especially poly(phenylenevinylene)] carrying
electron-withdrawing substituents such as cyano or nitro groups
(Friend, R. H. et al. Nature, 395, 257-259, 1998; Holmes et al.
Angew. Chemie. In. Ed., 37, 402-428, 1998), polymers containing
oxadiazole, quinoxaline, or pyridine units (Bradley, et al. Appl.
Phys. Left., 69, 881-883, 1996; Holmes et al. Angew. Chemie. In.
Ed., 37, 402-428, 1998; Andersson et al. Macromolecules, 35,
1638-1643, 2002), and a few ladder polymers such as BBL
({poly(7-oxo,
10H-benz[de]imidazo[4',5:5,6]-benzimidazo[2,1-a]isoquinoline-3,4:10,11-te-
trayl)-10-carbonyl}) (Sherf, U. "Conjugated Ladder-Type
Structures," in Handbook of Conducting Polymers, 2.sup.nd Ed.", Ed.
T. A. Skotheim, R L Elsenbauer, J. R. Reynolds, Marcel Dekker, New
York, 363-379, 1998). Unfortunately, current n-type semiconducting
polymers have generally poor properties, including low charge
carrier density and low carrier mobility. Furthermore, most of
these materials are difficult to process, and some of them are
difficult to synthesize.
[0009] In some cases, n-type semiconducting non-polymeric species,
such as functionalized fullerenes, molecular glasses and metal
complexes, are used instead of polymers (Strohriegl, P. et. Al,
Advanced Materials, 14, 1439-1451, 2002; Shaheen, S. et. al., Appl.
Phys. Lett., 78, 841-843, 2001). The disadvantage of these
non-polymeric semiconducting species is the low charge carrier
mobility due to the limited conjugation (due to low molecular
weight), and the fact that they often need to be processed by
vacuum deposition techniques. Thus, there is a significant need in
the art for new n-type conducting and semiconducting materials that
have improved charge carrier mobility, which are more readily
processed and synthesized. The present invention provides n-type
semiconducting polymers which provide such improvements.
[0010] There are two basic ways to make a pi-conjugated polymer
structure that is electron deficient. First, as noted above, the
conjugated backbone of the polymer can be chemically modified by
substitution with electron withdrawing substituent groups, such as
cyano or nitro groups. Such pendant modification is effective to
impart some electron deficiency to the pi-conjugated polymer. For
example, poly(para-phenylene vinylene) has been modified with cyano
and other pendant groups to produce a pi-conjugated semiconducting
polymer with n-type properties (Granstrom et al. Nature 395,
257-260, 1998). A second and more effective way to impart n-type
semiconducting properties is to directly modify the backbone of the
polymer with electron deficient atoms or organic structures. Holmes
et al. prepared pi-conjugated oxadiazole-containing polymers that
exhibited n-type semiconducting properties and photoluminescence
(Li et al. J. Chem. Soc. Chem. Commun. 2211-2212, 1995). Yamamoto
et al. prepared pi-conjugated quinoxaline-containing polymers that
also exhibited n-type semiconducting properties, photoluminescence,
and electroluminescence. Both the oxadiazole and quinoxaline
structures are known to impart electron deficiency in molecules.
Similarly, Babel and Jenekhe. prepared pi-conjugated polymers
incorporating regioregular dioctylbithiophene and
bis(phenylquinoline) units in the backbone of the polymer and
demonstrated both PLED(polymer light-emitting diodes and OFET
(organic field-effect transistors) prototype devices utilizing
these materials (Babel, A., Jenekhe, S. A. Adv. Mater., 14,
371-374, 2002).
[0011] Certain non-polymeric, pi-conjugated, organoboron molecules
have been observed to be electron deficient (Noda et al. J. Am.
Chem. Soc. 120, 9714-9715, 1998; Matsumi et al. Polymer Bulletin
50, 259-264, 2003). This is due to the valence electronic structure
of the boron atom and its ability to form multiple stable bonds
with carbon atoms. The empty p-orbital of boron can join in the
pi-conjugated system without any added electron density (Zweifel et
al. J. Organomet. Chem. 117, 303-312, 1976). The possibility of
delocalization of pi electrons between the vacant p orbital of
boron and the pi orbitals of conjugated organic substituents has
been extensively studied on mono- and di-vinylhaloboranes and
trivinylborane. These molecules exist only in a planar
conformation, suggesting that there is, in fact, delocalization of
the vinyl pi electrons over the boron atom (Pelter, A., and Smith,
K. "Triorganylboranes," in Comprehensive Organometallic Chemistry,
Vol 3, 792-795, 1979). Theoretical calculations performed with the
LCAO and self-consistent field methods (Good, C. D., and Ritter, D.
M. J. Am. Chem. Soc., 84, 1162-1165, 1962) as well as .sup.13C-NMR
studies (Yamamoto, Y. and Moritani, I. J. Org. Chem., 40,
3434-3437, 1975) also predict considerable delocalization of the
vinyl pi electrons over the carbon-boron bonds. Marder et al.
reports that three-coordinate boron species are equivalent to
carbonium ions, and are thus extremely electron-deficient systems.
However, if the boron is sterically protected, for example, with
bulky trimethylphenyl groups, the resultant materials are
air-stable (Marder et al. J. of Solid State Chemistry, 154, 5-12,
2000). Kaim and co-workers report that low molecular weight,
non-polymeric, pi-conjugated organoboron compounds have redox
properties that are analogous to nitrogen-containing pi-conjugated
molecules. In fact, under chemical or electrochemical reduction,
organoboron compounds form a series of anions of the type:
--BR.sub.2, --BR.sub.2.sup..cndot.-, .dbd.BR.sub.2.sup.-, while
nitrogen-containing compounds upon oxidation form the series of
cations: --NR.sub.2, --NR.sub.2.sup..cndot.+, .dbd.NR.sub.2.sup.+
(Fiedler et al. Inorg. Chem., 35, 3039-3043, 1996). This indicates
that pi-conjugated organoboron compounds are redox active and are
effectively easy to reduce. The use of certain organoboron,
non-polymeric pi-conjugated molecules as an electron transport
layer (ETL) in molecular organic light-emitting diodes is reported
by Shirota and Noda. These authors report an improvement in maximum
luminescence by a factor of 1.6 to 1.8 compared to an identical
single layer device that does not contain the organoboron ETL
(Shirota Y. and T. Noda J. Am. Chem. Soc., 120, 9714-9715, 1998).
The organoboron ETL materials of Shirota and Noda are non-polymeric
molecules of defined structure having a specific molecular weight
and are not pi-conjugated organoboron polymers.
[0012] Chujo et al. have reported non-conjugated, organoboron
polymers in which sterically bulky organic groups are appended to
the boron atoms adjacent to the polymer chain. The authors
concluded that the bulky protecting groups on boron led to stable
non-conjugated polymers with weight average molecular weights that
remained stable with constant exposure to air for two weeks (Chujo
et al. Polymer 41, 5047-5051, 2000). Chujo and co-workers have also
reported a number of pi-conjugated, organoboron polymers that make
use of bulky protecting groups (Matsumi et al. J. Am. Chem. Soc.,
120, 10776-10777, 1998; Matsumi et al. J. Am. Chem. Soc., 120,
5112-5113, 1998; Miyata et al. Polymer Bulletin, 42, 505-510, 1999;
Matsumi et al. Macromolecules, 32, 4467-4469, 1999; Matsumi et al.
Polymer Bulletin, 44, 431-436, 2002). These polymers have
absorption maxima in the visible region and are highly fluorescent
when irradiated with UV light, suggesting the existence of an
extended .pi.-conjugation across the boron atoms. The polymers are
also soluble in common organic solvents and stable in air and
moisture in the pristine (undoped) state. Chujo and co-workers have
also reported the n-doping of a pi-conjugated, organoboron polymer
with triethylamine to a conductivity of 10.sup.-6 S/cm (Kobayashi
et al. Synthetic Metals, 135-136, 393-394, 2003). The n-type
semiconducting properties and photoluminescence of these materials
have been reported, but the materials were not shown to be useful
in thin film, organic polymer electronic devices, such as OPVs
(organic photovoltaics), PLEDs, or OFETs.
[0013] Jakle studied multiborylated polythiophenes for use in
chemical sensors (Sundararraman., et al., JACS, 127, 13748-13749,
2005) and Siebert and co-workers reported the synthesis of certain
pi-conjugated organoboron polymers containing thiophene units by
hydroboration polymerization (Corriu et al., Chem. Commun., 963-964
1998)
[0014] U.S. Pat. Nos. 3,269,992, 3,203,909, 3,203,930, 3,203,929,
3,166,522, and 3,109,031 report the preparation of certain
organoboron polymers. U.S. Pat. No. 6,025,453 reports the
composition of polymers containing at least an alkynyl group, at
least one silyl group and at least one boranyl group and their use
for making high temperature oxidatively stable thermosetting
plastics.
SUMMARY OF THE INVENTION
[0015] This invention relates to the use of certain pi-conjugated
polymers in thin-film organic polymer electronic devices. These
polymers all contain boron atoms in the pi-conjugated backbone of
the polymer and therefore are electron-deficient and exhibit n-type
semiconducting properties, photoluminescence, and/or
electroluminescence.
[0016] The invention provides thin-film, organic polymer electronic
devices which comprise at least one active layer containing a thin
film of a pi-conjugated organoboron polymer and at least two
electrodes in contact with the active layer. The thin film of the
pi-conjugated organoboron polymer can be 100 angstroms to 10000
angstroms in thickness. Preferably the thin film of the
pi-conjugated organoboron polymer is 100 angstroms to 3000
angstroms in thickness.
[0017] The devices of this invention include those which exhibit
current rectification or diode-like properties. The devices of this
invention include those wherein the thin film comprises a
pi-conjugated organoboron polymer that emits light under a voltage
bias.
[0018] The invention also provides devices wherein the active layer
of the device contains, in addition to the thin film of the
pi-conjugated organoboron polymer, a light-emitting thin film which
comprises a light-emitting polymer which is not a pi-conjugated
organoboron polymer, a light-emitting non-polymeric molecule, or an
inorganic light emitting compound.
[0019] The invention further provides devices having an active
layer which comprises at least one thin film that in turn comprises
one or more pi-conjugated organoboron polymers blended with one or
more light-emitting molecules, or polymers or an inorganic
compound. The invention provides devices having an active layer
comprising at least one thin film of a pi-conjugated organoboron
polymer blended with a different organic or inorganic conducting or
semiconducting material. This organic or inorganic conducting or
semiconducting material may be one or more polymers, one or more
non-polymeric molecules, one or more inorganic compounds, or a
mixture thereof. More particularly, the active layer of the devices
herein can comprise at least one thin film containing a p-type
conducting or semiconducting polymer that is not a pi-conjugated
organoboron polymer blended with a pi-conjugated organoboron
polymer. In other embodiments, the active layer of the devices
herein comprises at least one thin film containing inorganic p-type
semiconducting particles mixed with a pi-conjugated organoboron
polymer. More specifically, inorganic p-type semiconducting
particles having at least one dimension less than 1000 angstroms
can be employed in active layers herein. Regioregular poly(n-alkyl
thiophene)s are examples of organic p-type semiconducting materials
and boron-doped silicon, p-type gallium arsenide and p-type zinc
telluride are examples of inorganic p-type semiconductors that can
be used in this invention.
[0020] Devices of this invention further include those wherein the
active layer further comprises an additional thin film of a
dielectric material that is in contact with one or more additional
electrodes. The layer of dielectric insulating material is usually
in contact with one of the electrodes as exemplified in FIGS. 2E
and 2F.
[0021] Representative structures of organoboron polymer
compositions useful in the devices of this invention are shown in
Scheme 1, formulas a-j. More specific structures of organoboron
polymers of this invention are shown in Scheme 2, formulas A-I.
Representative synthetic methods are shown in Examples 1, 2 and
7.
[0022] The invention also provides certain novel pi-conjugated
organoboron polymers and oligomers which exhibit beneficial
properties for application in thin-film organic polymer electronic
devices.
[0023] Novel polymers of this invention include pi-conjugated
organoboron polymers and oligomers that do not contain an aromatic
ring in the polymer backbone. However, the novel polymers of this
invention may contain one or/more aromatic rings in a side chain,
as substituents on the boron atoms or as substituents of the
unsaturated carbon atoms of the polymer backbone. The novel
polymers of this invention include, among others,
poly(vinylborane)s, poly(acetylenylborane)s, poly(divinylborane)s,
poly(vinyl acetylenylborane)s, and poly(polyenylborane)s.
Representative structures of these novel organoboron polymer
compositions useful in the devices of this invention are shown in
Scheme 1, formulas a, f and g. More specific structures of novel
organoboron polymers of this invention are shown in Scheme 2,
formulas D. Representative synthetic methods of these novel
polymers are shown in Example 2. Novel polymers of this invention
can exhibit improved properties over prior art polymers,
particularly those reported by Chujo and coworkers, because the
higher density of boron atoms can provide higher
electron-deficiency.
[0024] Novel polymers of this invention also include
poly(9,9-dialkylfluorenylborane)s. Examples of these polymers
include polymers 3dx, 3dy, 3ex, 3ey, and 3gx of Scheme 4.
Representative synthetic methods of these novel polymers are given
in Example 1. These novel polymers can provide improved properties
compared to known polymers because of their specific light emitting
properties (color and intensity).
[0025] Novel polymers of this invention also include structures E,
F, G, H, and I of Scheme 2. Representative synthetic methods of
these novel polymers are given in Example 7. These novel polymers
can provide improved properties compared to known polymers because
of the higher electron deficiency of the aromatic unit.
[0026] Methods or improved methods for synthesis of certain
pi-conjugated organoboron polymers are also provided. A significant
improvement of the method of preparation of poly(arylborane)s
polymers 3a-3e over prior art methods is the use of an
organolithium derivative rather than a Grignard reagent and the use
of cyclohexane (a cyclic hydrocarbon) rather than tetrahydrofurane
(THF) or other oxygenated solvent. The improved methods provide
polymers having boron atoms that are free from coordination, while
prior art methods provide polymers having the boron atoms
coordinated to the solvent. Coordination with the solvent partially
fills the empty p orbital of the boron atoms and decreases the
electron-deficiency of the polymer.
[0027] The invention further provides methods for making thin films
containing pi-conjugated organoboron polymers for use in thin-film
organic polymer electronic devices and methods for making such
devices employing thin films containing pi-conjugated organoboron
polymers.
[0028] The invention additionally provides methods employing
thin-film organic polymer electronic devices that contain an active
layer comprising one or more pi-conjugated organoboron polymers as
photovoltaic cells, diodes, photodiodes, TFTs, OFETs, printable or
flexible electronics like radio-frequency identification (RFID)
tags, electronic papers, printed circuit elements, organic light
emitting diodes (OLED)s, PLEDs, and energy storage devices.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1. Cyclic voltammetry of a thin film of polymer 3ay.
Arrows indicate direction of the voltage sweep.
[0030] FIG. 2. Exemplary configurations of various thin-film
organic polymer electronic devices containing a layer of a
pi-conjugated organoboron polymer.
[0031] FIG. 3. Current versus voltage response of a MEH-PPV diode
with a 3by layer acting to transport electrons.
DETAILED DESCRIPTION OF THE INVENTION
[0032] This invention relates to the use of pi-conjugated polymers
comprising both organic conjugated repeat units and organoboron
units in thin-film, organic polymer, electronic devices.
[0033] An individual polymer molecule is a molecule comprising a
plurality of repeating units. For clarity herein, a polymer
molecule is defined as containing four or more repeating units of
the same type, or four or more repeating units of at least one type
of repeating unit, if different repeating units are presents. The
four repeating units in a polymer molecule need not be contiguous
in the molecule. Individual molecules containing two or three
contiguous or non-contiguous repeating units of the same type are
defined herein as oligomer molecules. Different repeating units can
be distributed in an ordered or random (non-ordered) fashion in the
polymer or oligomer molecule. Polymer molecules and oligomer
molecules are thus distinguished from non-polymeric molecules which
do not contain repeating units. A polymer molecule may comprise a
linear chain of four or more repeating units or may comprise
branched chains of four or more repeating units. Similarly,
oligomers may be linear or branched. Polymer and oligomer molecules
optionally contain end groups that differ in structure and
chemistry from the repeating units.
[0034] In general, because of the way that they are prepared,
polymers are a mixture of polymer molecules comprising a
statistical distribution of individual polymer molecules which
contain a different number of repeating units, or a different
ordering of more than one repeating unit. Each individual polymer
molecule in the polymer has a specific chemical structure and
molecular weight. However, the polymer is a mixture of individual
polymer molecules. Unless otherwise specified herein the term
polymer refers to such mixtures of individual polymer molecules.
Polymers may also contain a mixture of oligomer molecules. Like
polymers, oligomers can be prepared as a mixture of individual
oligomer molecules with different numbers of repeating units or a
different order of repeating units if more than one repeating unit
is present. Because oligomers contain fewer repeating units the
diversity of structures present in a mixture of oligomers is less
than in polymers.
[0035] Therefore polymers (mixtures of individual polymer
molecules) are characterized by their "weight average molecular
weight," also called "weight average molar mass" that is defined
as: <M>.sub.w=(.SIGMA. w.sub.i M.sub.i)/(.SIGMA. w.sub.i),
where < > indicates that it is an average,
w.sub.i=N.sub.iM.sub.i/N.sub.A, where N.sub.i is the number of
molecules of the polymer i having molar mass M.sub.i. [J. M. G.
Cowie, "Polymers: Chemistry & Physics of Modern Materials",
2.sup.nd Edition, Blackie Academic & Professional, Great
Britain, (1993), pages 8-9]. The weight average molecular weight is
typically measured by Gel Permeation Chromatography (also called
size exclusion chromatography) using either a light scattering or a
refractive index detector, using appropriate standards of known
mass [J. M. G. Cowie, "Polymers: Chemistry & Physics of Modern
Materials", 2.sup.nd Edition, Blackie Academic & Professional,
Great Britain, (1993), pages 210-214]. The chain length of polymers
can also be described by the "average degree of polymerization
x.sub.w" where x=<M>.sub.w/M.sub.0, where M.sub.0 is the
molar mass of a monomer (repeating unit) and <M>.sub.w is the
weight average molar mass as defined above. As known in the art,
polymers may also be characterized by a "number average molecular
weight" or the "z-average" both of which are terms that are
well-known in the art.
[0036] According to this invention polymers encompass oligomeric
and telomeric compounds and any mixtures containing a distribution
of polymer molecules having the same four or more repeating units,
but having different molecular weights or having a different
ordering of repeating units. In specific embodiments, polymers of
this invention include those in which the average degree of
polymerization is 10 or more. In other specific embodiments,
polymers of this invention include those in which the average
degree of polymerization is 20 or more. In other specific
embodiments, polymers of this invention include those in which the
average degree of polymerization is 50 or more.
[0037] The term "organic" refers to a chemical species, i.e., a
molecule, moiety, radical, or functional or substituent group,
which contains a single carbon atom (substituted with hydrogen or
other substituent group, e.g., CH.sub.3--, CF.sub.3--,
CH.sub.3--NH--CH.sub.2--) or contains covalently bonded carbon
atoms and optionally contains various other atoms in addition to
carbon and hydrogen. The bonds between carbons may be single,
double, triple or aromatic (as in benzene). Carbons may be bonded
in a linear chain, a branched chain, or a ring which may be an
aromatic ring.
[0038] The term organic polymer refers to a polymer comprising
organic polymer molecules in which at least one of the repeating
units is an organic moiety which contains covalently bonded carbon
atoms and optionally contains various other atoms. Typically an
organic moiety contains a carbon-carbon bonded backbone or ring
structure which may be substituted with various substituents (other
than hydrogen) containing various atoms or in which the backbone
remains predominantly composed of carbon, but may contain other
atoms (e.g., O, S, N, etc.). Organic polymers may be formed having
more than one repeat unit that are different in structure from each
other, and are distributed along the polymer chain in any ordered
or random arrangement or sequence. Therefore, the term polymer
herein encompasses also random, alternated and block
copolymers.
[0039] A monovalent organic radical (or simply a monovalent
radical) is a group of atoms (molecular fragment) derived formally
by removal of a single hydrogen atom from an organic molecule.
Examples of monovalent organic radicals include, among others,
CH.sub.3-- (methyl radical), CH.sub.3--CH.sub.2--,
OH--CH.sub.2--CH.sub.2--, C.sub.6H.sub.5--CH.sub.2--, and
CH.sub.3--CH.dbd.CH--. Additional organic radicals are species
derived formally by removal of a single hydrogen atom from a
non-carbon atom (e.g., O, N, S, Si) in the organic molecule, such
as alkoxide radicals (R--O--, where R is an alkyl or other organic
group), which is derived by removal of hydrogen from an alcohol, an
amine radical (RR'--N--, where one of R or R' is an alkyl or other
organic group), or a silyl radical (R.sub.3Si--, where R is an
alkyl or other organic group).
[0040] A divalent organic radical (or simply a divalent radical) is
a group of atoms (molecular fragment) derived formally by removal
of two hydrogen atoms from an organic molecule where both hydrogens
may be removed from the same atom in the organic molecule or two
different atoms in the organic molecule. Exemplary divalent organic
radicals are: --CR.sub.2--, --CF.sub.2--, --C.sub.6R.sub.4-- (a
phenylene radical), --(CR.sub.2).sub.n--,
--(CR.sub.2).sub.n--X--(CR.sub.2).sub.m--, --X--(CH.sub.2)--,
--NR''--, where n and m are integers, each R, independent of other
R's is hydrogen, halogen, alkyl or other organic group, R'' is an
organic group and X is O, S, NR, CO, CS, NRCO, COO, double bond,
triple bond, or phenylene, among others.
[0041] A multivalent organic radical (or simply a multivalent
radical) is a group of atoms (molecular fragment) derived formally
by removal of three or more hydrogen atoms from an organic
molecule. Examples of multivalent radicals include --(R)C<,
--(CR.sub.2).sub.n--CR<, --(CR.sub.2).sub.n--X<,
--(CR.sub.2).sub.n--X(-)-(CR.sub.2).sub.m--Y--,
--(CR.sub.2).sub.n--X(-)-(CR.sub.2).sub.m--, where n and m are
integers, each R, independent of other R's is hydrogen, halogen,
alkyl or other organic group, X is N, CR, N--CO, and Y is CR.sub.2,
CO, COO, CS, O, S, NR, NR--CO, and phenyl (C.sub.6R.sub.4),
[0042] Organic radicals can contain linear or branched carbon
chains or rings containing carbon and other atoms (e.g., O, S, N).
Organic radicals can contain double bonded carbons, triple bonded
carbons, non-aromatic or aromatic rings. Carbons in organic
radicals can be substituted with one or more various non-hydrogen
substituents, including halogens, amino group, alkoxide or
hydroxide groups, alkyl thiols or thiols, oxygen or sulfur (to form
CO or CS groups).
[0043] A functional group is a combination of atoms (or in the case
of halides a single atom) that when attached to an organic radical
has either a specific reactivity or imparts to the molecule a
specific character, for example, by electron withdrawing or
electron donating action. Hydrogen is not a functional group.
[0044] Typical functional groups include halogen atoms, nitro
groups, cyano groups, cyanate groups, thiocyanate groups,
isocyanate groups, thioisocyanate groups, alcohol groups (e.g.
organic groups with one or more OH groups), polyol groups (e.g.,
organic groups with more than one and more typically a plurality of
OH groups), alkoxide groups, ether groups (e.g., alkyl or other
organic groups containing one or more C--O--C linkages), thiols,
thioether groups (e.g., alkyl or other organic groups containing
one or more C--S--C linkages), silyl (e.g., R.sub.3Si--, where R is
various substituents or organic groups), siloxy (e.g.,
R.sub.2--Si(OR)--), aldehyde groups (organic radicals containing a
--COH moiety), ketone groups (organic radicals containing a CO
moiety), carboxylic acids (organic radicals containing --COOH
groups or --COO.sup.- groups, carboxylic ester groups (organic
groups containing --COOR'' groups, where R'' is an alkyl group or
other organic group), acyl halide groups (organic groups containing
--COX groups where X is a halide), anhydride groups (an organic
group containing an anhydride group), groups containing other
carboxylic acid derivatives, amino groups, alkyl amino groups,
amino oxide groups and groups containing other derivatives of amino
groups, diazo groups, azide groups, phosphoric acid ester groups,
alkyl phosphate groups and groups containing other phosphoric acid
derivatives, phosphinic acid groups, and groups containing
phosphinic acid derivatives, phosphine groups, groups containing
phosphonium salts, sulfuric acid ester groups, sulfate groups,
sulfonate groups, groups containing sulfinic acid derivatives,
groups containing sulfonium salts, groups containing oxonium salts,
groups containing carbon-carbon double bonds (e.g., alkenyl groups)
and groups containing carbon-carbon triple bonds (e.g., alkynyl
groups), and combinations thereof. Functional groups include
organic functional groups.
[0045] Many other functional groups are known in the art. Aldehyde
groups, halogen atoms, isocyanate groups and acyl halide groups are
examples, among many others, of functional groups that may be used
to impart a desired reactivity to a molecule or polymer. Nitro
groups, cyano groups, chlorine and bromine atoms, and carboxylic
acid derivatives are examples, among many others, of functional
groups with electron-withdrawing properties. Alcohol groups,
alkoxide groups, thiol groups, mercapto groups, and amino groups
are examples, among many others, of groups with electro-donating
properties. The terms "electron-withdrawing group: and
"electron-donating group" are terms that are well known in the art
of chemistry. Many groups are known in the art which are classified
into one of these groupings. These terms are used herein to have
their broadest meaning in the art. One of ordinary skill in the art
understands the meaning of these terms and knows how to select
functional groups which will function as an electron-withdrawing
group or an electron-donating group in a particular molecular
structure.
[0046] A conjugated compound is a compound that contains one or
more bonding orbitals that are not restricted to two atoms, but
they are spread (or delocalized) over three or more atoms. A
pi-conjugated (or .pi.-conjugated) compound is a compound in which
the delocalized molecular orbitals are made by overlap of atomic p
orbitals such as the remaining (non hybridized) p orbital of an
sp.sup.2 hybridized carbon atom (M. B. Smith and J March, "March's
Advanced organic Chemistry, Delocalized Chemical Bonding" 5.sup.th
Ed. John Wiley and Sons, 2001, p 32-33). This continuum of pi bonds
defines pi-conjugation, often referred to simply as conjugation,
and is most commonly observed in unsaturated or aromatic organic
molecules. Chemical species other than molecules, including
radicals, moieties and groups may be conjugated.
[0047] Organic molecules include saturated, unsaturated and
aromatic organic molecules. Chemical species other than molecules,
including radicals, moieties and groups may be saturated,
unsaturated or aromatic or contain portions that are saturated,
unsaturated or aromatic. In a saturated organic molecule, each
carbon has four bonds to other carbons, hydrogens, non-hydrogen
substituents, or functional groups (that do not contain double or
triple bonds). Exemplary saturated organic groups are alkyl groups
which may be straight-chain, branched or cyclic alkyl groups, and
which are optionally substituted with one or more non-hydrogen
substituents, such as halogens, hydroxide groups, alkoxide groups,
thiol groups, thioalkyl groups, ether groups, thioether groups,
silyl groups (e.g., R.sub.3Si- groups) and/or amino groups, among
others.
[0048] Unsaturated organic molecules are molecules containing at
least one carbon-carbon or carbon-heteroatom double bond (e.g.,
C.dbd.O, C.dbd.S, C.dbd.N). Exemplary unsaturated organic groups
are alkenyl groups and alkynyl groups which may be straight-chain,
branched or contain one or more rings groups, and which are
optionally substituted with one or more non-hydrogen substituents,
such as halogen atoms, or unsaturated functional groups (e.g., as
listed above) and alkyl groups which are substituted with
unsaturated functional groups, such as aldehyde and/or ketone
groups (containing --COH or --CO--), carboxylic acid, carboxylate
or carboxylic ester groups (containing --CO--O--), acyl halide
groups, cyanide groups, isocyanide groups, among many others.
Chemical species other than molecules, including radicals, moieties
and groups may be unsaturated.
[0049] Aromatic organic molecules are defined in M. B. Smith and J
March, "March's Advanced organic Chemistry, Delocalized Chemical
Bonding" 5.sup.th Ed. John Wiley and Sons, 2001, p 46-48). Aromatic
molecules may carry additional substituents including, halogens,
organic functional groups, and organic radicals (substituents may
be saturated and/or unsaturated groups). Chemical species other
than molecules, including radicals, moieties and groups may be
aromatic or contain portions that are aromatic. Aromatic organic
radicals are molecular fragments formally obtained by removal of a
hydrogen atom from the aromatic portion of an aromatic
molecule.
[0050] A pi-conjugated polymer is an organic polymer comprising
pi-conjugated repeat units in which one or more bonding orbitals
are delocalized over at least two repeat units. A pi-conjugated
organoboron polymer is a polymer made of repeat units that comprise
both unsaturated and/or aromatic units and boron atoms, wherein the
vacant p-orbital of the boron atoms conjugate with the
pi-conjugated orbital system of the aromatic and/or unsaturated
units. In a preferred embodiment the boron atoms are trivalent
(i.e. carry three substituents) and are sp.sup.2 hybridized.
Repeating units of these polymers optionally contain one or more
hydrogen substituents, including halogens or organic functional
groups.
[0051] A semiconductor is a material in which the uppermost band of
occupied electron energy states is completely full at the
temperature of 0 K (and without excitations). It is well-known from
solid-state physics that electrical conduction in solids occurs
only via electrons in partially-filled bands, so conduction in pure
semiconductors occurs only when electrons have been
excited-thermally, optically, or by other known means, into higher
unfilled bands. At room temperature, a proportion (generally very
small, but not negligible) of electrons in a semiconductor have
been thermally excited from the "valence band," to the "conduction
band." Semiconductors generally have bandgaps of approximately a
few electron-volts, while insulators have bandgaps several times
greater.
[0052] An n-type semiconductor is a semiconductor in which the
conduction electron density exceeds the hole density and in which
the electrical conduction is mainly due to the movement of these
excess electrons.
[0053] A thin-film is defined as a continuous stratum of any
material that is between 1 angstrom and 10,000 angstroms thick, and
more preferably 100 to 10,000 angstroms thick.
[0054] A thin-film, organic electronic device is defined as a
device comprising an active layer made of at least one thin-film
comprising a semiconducting or conducting organic molecule or
organic polymer in contact with two or more conducting materials
acting as electrodes to which a current or voltage is applied or
from which a current or voltage is obtained. Examples of thin-film
organic electronic devices include, but are not limited to OPVs,
organic diodes, organic photodiodes, organic TFTs, OFETs, printable
or flexible electronics like RFID tags, electronic papers, printed
circuit elements, OLEDs, PLEDs, thin-film capacitors and other
energy storage devices. When the device is turned on the active
layer exchanges charge carriers with one or more of the
electrodes.
[0055] A thin-film, organic polymer, electronic device is defined
as a device comprising an active layer made of at least one
thin-film comprising a semiconducting or conducting organic polymer
in contact with two or more conducting materials acting as
electrodes to which a current or voltage is applied or from which a
current or voltage is obtained. The terms conducting, conduction,
and conductivity all refer to electronic or electrical conductivity
and are not intended to refer to or imply ionic or thermal
conductivity. As known by those of ordinary skill in the art, the
active layer of a thin-film, organic polymer, electronic device may
contain more than one stratum, typically a plurality of strata, of
thin films of other materials or blends of materials, including but
not limited to organic or inorganic molecules and polymers that
have semiconducting, conducting or non-conducting properties. These
additional strata may play different roles in the device including,
but not limited to: hole transporting layers (HTL), hole injecting
layers (HIL), electron transporting layers (ETL), electron
injecting layers (EIL), singlet light-emitting layers, triplet
light-emitting layers, electron blocking layers, hole blocking
layers, flattening layers, photon absorbing layers, barrier layers,
charge separating layers, and dielectric layers.
[0056] An active layer of an electronic device is a layer
comprising one or more thin films of semiconducting, conducting, or
non-conducting materials and blends thereof. An active layer has a
function in the electronic device other than providing mechanical
strength to the device or acting as a substrate to carry an active
layer. For example, the active layer may have one or more of the
following functions: hole transporting, hole injecting, electron
transporting, electron injecting, singlet light emission, triplet
light emission, electron blocking, hole blocking, surface
flattening function, photon absorption, barrier function, charge
separation, and dielectric function.
[0057] In one embodiment of this invention the active layer
comprises a single thin-film of a pi-conjugated organoboron
polymer. In another embodiment, the active layer comprises a single
thin-film made of a blend or mixture of materials, at least one of
which is a pi-conjugated organoboron polymer. In yet another
embodiment of this invention the active layer of the device
comprises two or more thin films of semiconducting materials, at
least one of which is a pi-conjugated organoboron polymer or a
blend containing a pi conjugated organoboron polymer. When two or
more thin-films are present in the active layer, these thin-films
are in contact with any adjacent thin-films and electrodes.
[0058] The devices of this invention include those which exhibit
current rectification or diode-like properties. Current
rectification is the conversion of alternating current into direct
current. A diode is a device that preferably allows current to flow
in one direction and not in the other. The devices of this
invention include those wherein the thin film comprising a
pi-conjugated organoboron polymer which emits light under a voltage
bias.
[0059] This invention relates to the use of a new type of
pi-conjugated polymer in thin-film organic polymer electronic
devices. These polymers all contain boron atoms in the
pi-conjugated backbone of the polymer and preferably exhibit one or
more of the following properties: n-type semiconducting properties,
photoluminescence, and electroluminescence.
[0060] Pi-conjugated organoboron polymers of this invention are
made of repeat units that comprise at least one boron atom and at
least an aromatic or unsaturated fragment, such that conjugation of
bonding orbitals extends over more than one repeat unit of the
polymer and across the vacant p-orbital of the boron.
[0061] The preferred pi-conjugated organoboron polymers have a
conjugated backbone comprised of unsaturated organic portions (or
fragments) or aromatic organic portions (or fragments), or a
mixture thereof and boron atoms which may be additionally
substituted with a hydrogen, deuterium, halogen atoms, an organic
functional group or an organic radical. Exemplary pi-conjugated
organoboron polymers, represented by repeating units in brackets,
are illustrated in Scheme 1, where each R, independent of other R's
in the repeating unit, and R.sub.1, independent of any R's, can be
hydrogen, deuterium, a halogen atom, or an organic radical, Ar
represents a divalent aromatic radical which may optionally carry
one or more other organic radical groups, substituent groups,
and/or functional groups described herein and "n", "m" and "p" are
integers indicating either the number of moieties present in a
given repeating unit or the average degree of polymerization of the
polymer dependent upon the structure illustrated. In Scheme 1,
R.sub.1 is a substituent on the boron atom.
[0062] The preferred unsaturated portions of the pi-conjugated
organoboron polymers are vinylene, ethynylene, 1,3-butadienylene,
and other divalent radicals comprising more than one conjugated
carbon-carbon double bond, carbon carbon-triple bond,
carbon-heteroatom double bond, carbon heteroatom triple bond, and
mixtures thereof. More preferred are vinylene, ethynylene, and
1,3-butadienylene. Most preferred is vinylene. Additional
unsaturated fragments may be oligomeric species comprising one or
more of the repeat units listed above. The unsaturated fragment may
optionally carry one or more substituent group including hydrogen,
deuterium, halogens, any organic functional groups, or any
monovalent, divalent or multivalent organic radicals.
[0063] The preferred aromatic portions (or fragments) are divalent
radicals resulting from the removal of two hydrogen atoms from
benzene (such as 1,4 phenylene, 1,3-phenylene, and 1,2-phenylene),
napthalene, diphenyl, pyridine, pyrimidine, triazine, pyrrole,
N-alkylpyrroles, N-substituted pyrroles, 3-substituted pyrroles,
furan, tetrazole, indole, purine, oxadiazole,
1,5-diphenyl-oxadiazole, quinoxaline, phenazine,
N,N'-dialkylphenazines, phenothiazine, N-alkylphenothiazines,
carbazole, N-alkylcarbazoles, thiophene, 3-alkylthiophenes,
3-substituted thiophenes, 3,4-disubstituted thiophenes,
thienothiophene, substituted thienothiophenes, bithiophene,
terthiophene, quaterthiophene, dialkyloxybenzenes, oxazole,
fluorene, 9,9-dialkylfluorenes and their substituted derivatives.
These aromatic fragments are optionally substituted with one or
more non-hydrogen substituents and/or functional groups as
described herein. More preferred fragments are divalent radical
fragments resulting from the removal of two hydrogen atoms from
benzene, thiophene, 3-alkylthiophenes, bithiophene, terthiophene,
quaterthiophene, dialkyloxybenzene, fluorene, 9,9-dialkylfluorenes
and derivatives thereof. Additionally, the aromatic fragments may
be oligomeric species comprising one or more of the repeating unit
listed above and their mixtures.
[0064] Additionally a combination of one or more unsaturated
fragment and one or more aromatic fragment can be used (Scheme 1,
formulas c,d,e,g, and j). The aromatic fragment may optionally
carry one or more substituents including hydrogen, deuterium,
halogens, any organic functional groups, or any monovalent,
divalent or multivalent organic radicals.
[0065] It is preferred that the R.sub.1 group (referring to Scheme
1) on the boron atom is a bulky group that provides steric
hindrance to the boron atoms and protects it from the attack by
nucleophiles and radicals, such as water and oxygen. Steric
hindrance occurs when functional groups on a molecule (or molecules
individually) that would normally react with each other or be
attracted to one another cannot interact due to their special
relationship because the bulkiness of a side chains physically
covers the reactive site or because, due to the shape or stiffness
of a molecule, the reactive groups cannot come into contact. The
preferred organic groups "R.sub.1" on the boron atoms are any
aliphatic or aromatic radicals including, but not limited to,
methyl, trifluoromethyl, ethyl, n-propyl, iso-propyl, n-butyl,
sec-butyl, t-butyl, thexyl, perfluorinated alkyls, phenyl,
perfluorophenyl, alkyl-substituted phenyl, linear and branched
alkyl groups, which optionally may carry additional functional
groups such as carbon-carbon double or triple bonds, ester groups,
cyano groups, nitro groups, halogens, alcohols, amines, ethers,
aryl groups, which optionally may carry additional substituents
such as alkyl groups and or functional groups such as carbon-carbon
double or triple bonds, ester groups, cyano groups, nitro groups,
halogens, alcohols, amines, ethers, and any other known organic
functional group or organic radical. More preferred sterically
bulky, organic groups are pentafluorophenyl,
di(trifluoromethyl)phenyl, thexyl, 2-ethylhexyl,
1,3,5-trimethylphenyl(mesityl), and
1,3,5-triisopropylphenyl(tripyl) groups.
[0066] Selected structures of preferred pi-conducting organoboron
polymers are shown in Scheme 2, wherein R.sub.1, independent of
other R.sub.1 in the repeating unit and R.sub.2, and R.sub.2, and
R.sub.3, independent of any R.sub.1, are hydrogens, deuterium
atoms, halogen atoms, or linear or branched alkyl radicals,
particularly alkyl radicals having 1-20 carbon atoms, which can be
optionally substituted with one or more non-hydrogen substituents
or functional groups as defined herein; R.sub.3 is hydrogen,
deuterium atom, halogen atom, or an alkoxide or mercapto group,
particularly wherein the group has 1-20 carbon atoms, and which can
optionally carry one or more additional non-hydrogen substituents
or functional groups as defined herein; R.sub.4 is an aliphatic
radical (a saturated or unsaturated organic radical) particularly
one which contains 1-20 carbon atoms, or an aromatic radical, such
as a phenyl or substituted phenyl group, n is an integer number and
m is a small integer number preferably 1 to 6, and most preferably
1 to 3. In the formulas B, C, F and G, R.sub.2 and R.sub.3 can also
represent multiple independent substituent and/or functional groups
on the rings shown. Additionally R.sub.2 and R.sub.3 can represent
groups that link two ring positions, such as alkylene, ether or
thioether linkages between two ring positions. The wavy line to the
R.sub.2 and R.sub.3 groups indicates, as is understood in the art,
that these groups may be attached at any ring positions in place of
hydrogens. Note that in formulas shown herein, as is conventional
in the art, hydrogen substituents are not shown. Further any one or
more hydrogen substituents on the aromatic rings in the formulas of
Scheme 2 can optionally be substituted with a non-hydrogen
substituent or functional groups as described herein. In
particular, any hydrogen substituent in the formulas can be
replaced with a halogen, e.g., a fluorine atom, or an alkyl group
having 1 to 3 carbon atoms.
[0067] In specific embodiments, pi-conjugated organoboron polymers
include those of formula A in Scheme 2 wherein R.sub.1 is an alkyl
group having 1 to 6 carbon atoms which is optionally substituted
with one or more non-hydrogen substituents, particularly one or
more halogens, such as fluorine, and R.sub.2 is an alkyl group
having 3 to 20 carbon atoms which is optionally substituted with
one or more non-hydrogen substituents, particularly one or more
halogens, such as fluorine. In specific embodiments, pi-conjugated
organoboron polymers include those of formula A in Scheme 2 wherein
R.sub.1 is a straight-chain or branched alkyl group having 1 to 6
carbon atoms and R.sub.2 is a straight-chain or branched alkyl
group having 6 to 12 carbon atoms. In more specific embodiments,
pi-conjugated organoboron polymers include those of formula A in
Scheme 2 wherein R.sub.1 is a methyl or propyl group, particularly
an isopropyl group and R.sub.2 is a straight-chain or branched
alkyl group having 6 to 12 carbon atoms. In more specific
embodiments, pi-conjugated organoboron polymers include those of
formula A in Scheme 2 wherein R.sub.1 is a straight-chain or
branched alkyl group having 1-6 carbon atoms and R.sub.2 is a
straight-chain alkyl group having 6-16 carbon atoms, and more
specifically a straight-chain alkyl group having 6 or 12 carbons
atoms or R.sub.2 is a branched alkyl group having 6 to 16 carbon
atoms and more specifically a branched alkyl group having 8-12
carbon atoms.
[0068] A preferred method of preparing pi-conjugated organoboron
polymers is by reacting the respective dibrominated unsaturated or
aromatic compounds with dimethoxymesitylborane or
dimethoxytripylborane in the presence of magnesium via the
formation of the Grignard reagent (as exemplified in Example 1).
Yet another preferred method of preparing pi-conjugated organoboron
polymers is by reacting di-lithiated unsaturated or aromatic
compounds with dimethoxymesitylborane, dimethoxytripyl-borane,
dichlorophenylborane or dichloro-t-hexylborane (as exemplified in
Example 3 and 4). Other organometallic coupling reagents may be
used for this application in place of the Grignard reagent or
lithium derivatives, including copper derivatives, tin derivatives,
nickel derivatives, and silyl derivatives. These methods can be
used to prepare, for example, compounds of the type of formula a, b
f and i in Scheme 1.
[0069] Compounds of the type g and h in Scheme 1 can be prepared by
reacting the dibromo derivative of an oligomeric or telechelic
species of the unsaturated or aromatic monomer with a borane
reagent. Oligomerization of the aromatic or unsaturated compound
and coupling with the borane reagent may occur in a single step if
the proper organometallic intermediate and the proper reaction
conditions are used. Preferred borane reagents are compounds
containing a trivalent boron atom that is substituted with an alkyl
or aryl group and two reactive groups such as alkoxy groups or
halogen atoms. Dimethoxymesitylborane, dimethoxytripylborane,
dichlorohexylborane and dichlorophenylborane are examples of borane
reagents.
[0070] Another preferred method to prepare pi-conjugated
organoboron polymers is by the hydroboration or dihydrobromination
of dialkynes (Chujo et al. J. Am. Chem. Soc., 120, 5112-5113, 1998;
Chujo et al. Polymer Bulletin, 42, 505-510, 1999). This method can
be used, for example, to prepare compounds of the type of formulas
e, g and j in Scheme 1.
[0071] Compounds of the type of formulas c and d in Scheme 1 can be
prepared by coupling of borane reagents with asymmetric
organometallic compounds or via more complex synthesis comprising
multiple steps or hydroboration and coupling.
[0072] Polymers of this invention, including those illustrated in
Schemes 1 and 2, can be readily prepared in view of the description
herein and methods that are well-known in the art. Those of
ordinary skill in the art will appreciate that methods other than
those specifically exemplified herein can be used to prepare the
desired pi-conjugated organoboron polymers.
[0073] Preferred pi-conjugated organoboron polymers comprise at
least two repeating units and have weight average molecular weights
ranging from 50 Dalton to one million Dalton as determined by Gel
Permeation Chromatography (GPC). More preferred polymers have
weight average molecular weights ranging from 500 to 100,000, and
most preferably from 3,000 to 30,000.
[0074] In a preferred embodiment the pi-conjugated organoboron
polymers are N-type semiconductors and have a non-negligible (i.e.,
measurable with current state-of-the art equipment) mobility of
charge carriers, preferably where the charge carriers are negative
charge carriers. Preferred charge carrier mobilities are greater
than 10.sup.-5 cm.sup.2/Vs with more preferred mobility being
greater than 10.sup.-3 cm.sup.2/Vs. Preferred carrier densities are
greater than 10.sup.6 cm.sup.-2 with more preferred carrier
densities greater than 10.sup.9 cm.sup.-2. Charge carrier type,
density, and mobility can be measured by carrying out Hall probe
measurements or by using a time of flight laser excitation
technique (ASTM F76 from the ASTM book of Standards Version 10.05,
2000). These properties are required when the pi-conjugated
organoboron polymers are used for the fabrication of transistors,
solar cells and for the electron transport layer of an OLED.
[0075] In another preferred embodiment the pi-conjugated
organoboron polymers of this invention are fluorescent,
electroluminescent and/ or emit light under applied bias. Typical
fluorescence is green- and/or blue. These properties are required
when the pi-conjugated organoboron polymer is the light emitter
(Example 5), for example, in a PLED.
[0076] In yet another embodiment the pi-conjugated organoboron
polymers of this invention are doped to a conducting state. This
can be achieved, for example, by reaction with a reducing agent
such as an alkali metal hydride, or a solution of sodium
naphthalenide, by ion implantation or by electrochemical methods
(Antoun, S., and R. D. Gagnon, J. D. Capistran, F. E. Karask, R. W.
Lenz., (1987). "Synthesis, doping, and electrical properties of
high molecular weight poly(p-phenylenevinylene)," Polymer, 28,
587-573, Moliton, A. (1998) "Ion Implantation Doping of
Electroactive Polymers and Device Fabrication," in Handbook of
Conducting Polymers, 2.sup.nd Ed." Ed. T. A. Skotheim, R L
Elsenbauer, J. R. Reynolds, Marcel Dekker, New York, p-589-638,
Shacklette, L. W., and J. E. Toth, N. S. Murthy, R. B. Baughman,
(1985) "Polyacetylene and Polyphenylene as Anode Materials for
Non-aqueous Secondary Batteries," J. Electrochem. Soc., 132,
1529-1535). Preferred conductivities are higher than 10.sup.-6 S/cm
and most preferred are higher than 10.sup.-3 S/cm. Most preferably,
the doping process is reversible and stable (Example 4).
[0077] Preferred pi-conjugated organoboron polymers are soluble in
common organic solvents at 0.1 g/L or more and more preferably at 1
g/L or more. In an embodiment of this invention, coating solutions
of pi-conjugated organoboron polymers are prepared by dissolving
the polymers in an appropriate solvent at an appropriate
concentration. Preferred solvents are alkanes, aromatic
hydrocarbons, ethers, alcohols, ketones, esters, nitrites,
lactones, nitroalkanes, halogenated alkanes, and supercritical
carbon dioxide. The most preferred solvents are benzene, toluene,
xylenes, pentane, hexanes, cyclohexane, tetrahydrofuran,
dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone,
dimethylcarbonate, acetonitrile, chloroform, dichloromethane,
dichloroethane. The concentration of a coating solution is in the
range of greater than 0 to 40% solids by weight, e.g., 0.01% to
10%, but preferably is 0.1% to 5% solids by weight. Common coatings
additives such as rheology modifiers, surfactants, wetting agents,
anti-foaming agents, and crosslinkers may be added to coating
solutions as an embodiment of this invention. These coating
solutions may be used to prepare coatings, patterned coatings,
printed circuitry elements, and other device elements or
features.
[0078] The preferred solubility properties of a given
boron-containing conjugated polymer depend on the device design in
which the polymer will be used (FIG. 2). In order to construct
layered materials, polymers for use in adjacent layers are selected
so that their solubility is either orthogonal to each other or
similar to each other. The term "orthogonal" with respect to
solubility is used to describe the situation where there exists at
least one solvent in which one of the two different polymers used
in adjacent layers is substantially more soluble than the second
polymer under selected conditions (temperature, contact time, etc.)
The term "similar" with respect to solubility is used to describe
the situation where there exists at least one solvent in which both
of the two different polymers are substantially soluble under
selected conditions. If polymers for use in adjacent layers have
substantially similar solubility in a given solvent, partial or
complete mixing of the two layers at the interface can occur during
spin casting. The different polymers need not exhibit the same
level of solubility in the given solvent under the selected
conditions. They need only have sufficient solubility in the
solvent to obtain the level of mixing desired. If the solubility of
the polymers for use in adjacent layers is substantially
orthogonal, then no significant level of mixing occurs in a given
solvent under selected conditions.
[0079] Again dependent upon device design and application, mixing
of the adjacent layers may be a desirable property (e.g., laminate
cell device of FIG. 2B) or a highly undesirable property (e.g.,
cell devices of FIG. 2C-F). In these cases the underlying layers
are cast from polar or aqueous solvents and therefore the
organoboron polymer is preferred to be soluble in non-polar
solvents. For these reasons it is desirable to control and change
the solubility properties of organoboron polymers for use in device
applications herein. This is achieved by selecting the nature of
the polymer side chains, by selecting functional groups for
inclusion on the polymer side chains and by selecting the average
molecular weight of the polymer itself. Tunable solubility
properties of polymers also facilitate the preparation of ideal
blends of the n-type boron-containing conjugated polymers with
other p-type conjugated polymers for use in photodiodes and
photovoltaic solar cells. Ideal blends contain phase separated
domains of the p-type and n-type materials, wherein the domains of
each phase are preferably small and have a fractal surface to
maximize the surface area (interface) that separates the two
materials. Maximizing the interface in such devices can be
beneficial because light generation (in OLEDs and PLEDs) and charge
separation (i.e. creation of current in photovoltaic devices) occur
at the interface.
[0080] In a preferred embodiment of this invention, coating
solutions may contain more than one polymer, for example they may
contain two or more pi-conjugated organoboron polymers or a mixture
of a pi-conjugated organoboron polymer with one or more other
pi-conjugated, conducting or semiconducting polymers (that are not
organoboron polymers) or non-polymeric molecules. In a more
preferred embodiment of this invention a coating solution may be
prepared with one or more pi-conjugated organoboron polymer and one
or more p-type conducting or semiconducting polymers that are not
organoboron polymers, p-type conducting or semiconducting
non-polymeric molecules, or p-type conducting or semiconducting
particulate solids. P-type conducting or semiconducting particulate
solids with physical dimensions smaller than 10 microns are
preferred. Regioregular poly(n-alkyl thiophene)s are examples of
organic p-type semiconducting polymers, zinc phthalocyanine and
hexathiophene are examples of p-type molecules and nano-crystalline
boron-doped silicon, p-type gallium arsenide and p-type zinc
telluride are example of inorganic p-type semiconductors.
[0081] Thin-films of this invention can contain polymer blends.
Polymer blends are macroscopically homogenous mixtures of two or
more measurably different polymers (noting that polymers themselves
are mixtures of polymer molecules). The polymers may be miscible,
but need not be miscible. Blends may contain different phase
domains in contrast to miscible polymer mixtures that contain a
single phase.
[0082] In an embodiment of this invention a thin film of a
pi-conjugated organoboron polymer or containing such a polymer is
formed by application of a coating solution to a substrate material
by appropriate means. Preferred methods include spin coating, dip
coating, contact printing, ink-jetting, screen printing, and
airbrushing. Removal of the coating solution solvent is preferably
carried out by evaporation with heating of the film to a
temperature in the range from room temperature to 250 degrees
Celsius and more preferably from 50 to 150 degrees Celsius for 5 to
30 minutes. Most preferably the thin film is annealed at 80 to 110
degrees Celsius for 5 to 10 minutes. If supercritical fluids are
employed as the solvent, temperatures below room temperature may be
used. Drying and annealing can be accomplished in air, but more
preferably is carried out under a flow of dry nitrogen or argon.
Dried thin films have a preferred thickness of 10 to 10,000
angstroms and a most preferred thickness of 100 to 5,000
angstroms.
[0083] In a preferred embodiment of this invention, thin films are
prepared on a substrate, which can be a glass, ceramic, plastic,
paper, textile, or metal substrate. These substrates can be of any
useful thickness and surface roughness. Preferred plastic
substrates are polyethylene, polypropylene, other polyolefins,
polyesters, polyacrylates, polycarbonates, polyvinylchloride,
polyvinylalcohol, polyvinylacetate, other vinyl polymers and
copolymers, polysulfones, polyamides, polyimides, polyolefins,
cellulose, cellulose acetate, Kapton, Kevlar, and perfluorinated
polymers. Optionally these substrates may be coated with any useful
thickness of films of metals, metal oxides, semiconductors,
dielectric materials, conducting polymers, or semiconducting
polymers. These films may be applied by any known means and
completely cover the substrate or be patterned by any known means
so as to provide the proper electrical properties and connections
for the operation of devices of this invention. In a preferred
embodiment of this invention the substrate may itself act as one or
more electrodes for the operation of devices of this invention. In
a preferred embodiment of this invention the substrate is glass or
plastic coated with a transparent, conducting oxide film comprising
tin-doped indium oxide or fluorine-doped tin oxide. In another
preferred embodiment of this invention the substrate is glass or
plastic coated with a transparent, conducting polymer comprising
polythiophene, polypyrrole, polyaniline, or derivatives thereof
(see Orgacon products by Agfa, Ormecon products by Ormecon, or
Baytron products by H. C. Starck).
[0084] Objects of this invention include thin-film, organic polymer
electronic devices that comprise one or more active layers and at
least two electrodes in contact with the active layer or layers,
wherein the electrodes provide a means by which a current or a
voltage is either applied to or derived from the active layer or
layers. The active layer or layers comprise at least one thin film
of an organic polymer. When only one active layer exists, that
layer comprises a pi-conjugated organoboron polymer. When the
active layers comprise more than one layer, then at least one of
the active layers is a pi-conjugated organoboron polymer. Examples
of various organic polymer electronic devices containing an active
layer of a pi-conjugated organoboron polymer are in FIGS. 2A-F.
[0085] FIGS. 2A and B schematically illustrate device
configurations useful particularly for diodes, photodiodes or
photovoltaic solar cells. FIG. 2A is a bended cell type device
configuration (10a) in which the active layer 5 is a thin film of a
polymer blend, e.g., a p-type semiconductor polymer and a
pi-conjugated organoboron polymer blend. The active layer (5) is
positioned between and separating two electrode layers (7a and 7b)
which are in electrical communication with two contacts (9a, 9b).
FIG. 2A illustrates a device constructed with a single substrate
layer (11a).
[0086] FIG. 2B illustrates a laminated-type cell device
configuration in which the active layer 5 comprises one or more
thin-film layers (multiple strata). This device configuration
contains two substrates (11a and 11b). Again the active layer
separates two electrodes (7a and 7b) each of which is in electrical
communication with contacts (8a and 8b) respectively.
[0087] FIGS. 2C and D illustrate exemplary device configurations
useful for diodes, light-emitting diodes and photodiodes. In FIG.
2C, the device is constructed with a single substrate (11a), the
active layer (5) is a light-emitting polymer layer which comprises
a pi-conjugated organoborane polymer that is light-emitting. The
active layer separates two electrodes (7a and 7b). The electrodes
are in electrical communication with two electrical contacts (8a
and 8b), respectively. In FIG. 2D, a two substrate device
configuration is illustrates. The active layer 5 comprises multiple
layers, including an electron transfer layer (15) which comprises a
pi-conjugated organoborane polymer and a light-emitting polymer
layer (17) comprising a light-emitting species, e.g., a light
emitting polymer (this polymer may or may not comprise or be a
pi-conjugated organoborane polymer.)
[0088] FIG. 2E illustrates a device configuration for an
OFET-bottom gate. Both configurations contain two substrates (11a
and 11b). The active layer 5 is positioned between a bottom
electrode (7a) and two separate top electrodes (7b and 7c). The
configuration has three contacts (8a, 8b and 8c) in electrical
communication with each electrode, respectively. The active layer 5
comprises a dielectric layer (19) adjacent the bottom electrode and
a pi-conjugated organoboron polymer comprising layer (21) between
the dielectric layer and in contact with top electrodes (7b and
7c).
[0089] FIG. 2F illustrates a device configuration for an OFET-top
gate. The active layer 5 is positioned between a top electrode (7a)
and two separate bottom electrodes (7b and 7c). The active layer 5
comprises a dielectric layer (19) adjacent the top electrode and a
pi-conjugated organoboron polymer comprising layer (21) between the
dielectric layer and in contact with bottom electrodes (7b and
7c).
[0090] It will be appreciated by those of ordinary skill in the art
that the pi-conjugated organoboron polymers and thin films
comprising them can be employed in additional device
configurations.
[0091] A more preferred object of this invention is a thin film,
organic polymer electronic device that is comprised of at least one
p-type semiconducting organic polymer layer and at least one
n-type, pi-conjugated organoboron polymer (as exemplified in FIGS.
2A and B). One or more electrode may constitute the substrate onto
which the organic polymer thin films are applied, or may be applied
as a layer on top of the thin film, organic polymer layers. In a
preferred embodiment of this invention, electrodes comprise metals,
metal oxides, semiconductors, conducting polymers, semiconducting
polymers or mixtures thereof. These electrode contacts may be
applied by any known means and completely cover the organic polymer
layers or be patterned by any known means so as to provide the
proper electrical properties and connections for the operation of
devices of this invention. In a more preferred embodiment of this
invention the electrode contacts are applied by thermal or physical
vapor phase deposition of aluminum, aluminum fluoride, copper,
nickel, gold, silver, magnesium, calcium, barium, zinc, titanium,
titanium oxide, fluorine-doped tin oxide, antimony-doped tin oxide,
tin-doped indium oxide, aluminum doped zinc oxide, or mixtures
thereof.
[0092] In one embodiment of this invention a thin-film of the
pi-conjugated organoboron polymer layer is used as the ETL in
OLEDs, PLEDs and other light emitting diodes to control the current
of injected electrons (from the cathode) such that they are
balanced with the current of injected holes (from the anode) under
forward bias (FIG. 2D). During such use of the pi-conjugated
organoboron polymer layer as an ETL, the device design may
additionally allow for light emission to occur (by singlet
recombination of electrons and holes) in this same layer. Therefore
the pi-conjugated organoboron polymer layer may be used as both an
ETL and a light-emitting polymer layer for PLEDs (FIG. 2D). In
another embodiment of this invention a thin film of the
pi-conjugated organoboron polymer is used as the light-emitting
layer of a PLED optionally in combination with a layer of a
different material that acts as the ETL (FIG. 2D).
[0093] In other embodiments of this invention, the pi-conjugated
organoboron polymer layer is similarly useful as the n-type
semiconductor and/or ETL in photodiodes. Such devices are similar
in design to PLEDs, but are typically operated under reverse bias
where photons produce a measurable induced photocurrent (by
photo-induced charge transfer and separation at the interface of
the p-type and an n-type semiconductor layers).
[0094] In additional embodiments of this invention, the
pi-conjugated organoboron polymer layer is similarly useful as the
n-type semiconductor and/or ETL in OPVs. Such devices are similar
in design to diodes, but are more preferably constructed with
active layers from blends of p-type and n-type semiconducting
polymers rather than separate layers of the p-type and n-type
semiconducting polymers. This blended active layer maximizes the
surface-to-volume ratio of the interface between p-type and n-type
semiconducting polymers where photo-induced charge transfer and
separation occurs, which is responsible for the generation of power
in these devices (FIG. 2A and B).
[0095] In further embodiments of this invention, the pi-conjugated
organoboron polymer layer is similarly useful as the n-type
semiconductor for the active layer in TFTs and OFETs (FIGS. 2E and
F). TFTs and OFETs may comprise a single semiconductor (n- or
p-type) or multiple semiconductors as in patterned p-n-p or n-p-n
junctions. Additional uses of n-type semiconductors in thin film
electronic devices are known by those skilled in the art.
Pi-conjugated organoborane polymers having n-type semiconductor
properties of this invention can be employed in all such
applications.
[0096] When a group of substituents is disclosed herein, it is
understood that all individual members of that group and all
subgroups, including any isomers, enantiomers, diastereomers, and
epimers of the group members, are disclosed separately. When
Markush groups or other groupings are used herein, all individual
members of the group and all combinations and subcombinations
possible of the various individual members of the various groups
are intended to be individually included in the disclosure and
useful in the practice of the invention. When a compound is
described herein such that a particular isomer, enantiomer,
diastereomer or epimer of the compound is not specified, for
example, in a formula or in a chemical name, that description is
intended to include each isomers and enantiomer of the compound
described individual or in any combination. Additionally, unless
otherwise specified, all isotopic variants of compounds disclosed
herein are intended to be encompassed by the disclosure. For
example, it will be understood that any one or more hydrogens in a
molecule disclosed can be replaced with deuterium or tritium.
Isotopic variants of a molecule are generally useful as standards
in assays for the molecule and in chemical research related to the
molecule or its use. Isotopic variants of molecules (or mixtures
thereof) can exhibit distinct properties in certain applications.
Methods for making such isotopic variants are known in the art.
Specific names of compounds are intended to be exemplary, as it is
known that one of ordinary skill in the art can name the same
compounds differently.
[0097] Formulas of polymeric species disclosed herein may contain
one or more ionizable groups [groups from which a proton can be
removed (e.g., --COOH) or added (e.g., amines) or which can be
quaternized (e.g., amines)]. All possible ionic forms of such
molecules and salts thereof are intended to be included
individually in the disclosure herein. With regard to salts of the
compounds herein, one of ordinary skill in the art can select from
among a wide variety of available counterions those that are
appropriate for preparation of salts of this invention for a given
application.
[0098] Every formulation or combination of components described or
exemplified herein can be used to practice the invention, unless
otherwise stated.
[0099] Whenever a range is given in the specification, for example,
a temperature range, a time range, or a composition or
concentration range, all intermediate ranges and subranges, as well
as all individual values included in the ranges given are intended
to be included in the disclosure. It will be understood that any
subranges or individual values in a range or subrange that are
included in the description herein can be excluded from the claims
herein.
[0100] All patents and publications mentioned in the specification
are indicative of the levels of skill of those skilled in the art
to which the invention pertains. References cited herein are
incorporated by reference herein in their entirety to indicate the
state of the art as of their publication or filing date and it is
intended that this information can be employed herein, if needed,
to exclude specific embodiments that are in the prior art. For
example, when a compound is claimed, it should be understood that
compounds known and available in the art prior to Applicant's
invention, including compounds for which an enabling disclosure is
provided in the references cited herein, are not intended to be
included in claims to compounds herein. However, certain
compositions claimed herein may contain components which are in the
prior art.
[0101] As used herein, "comprising" is synonymous with "including,"
"containing," or "characterized by," and is inclusive or open-ended
and does not exclude additional, unrecited elements or method
steps. As used herein, "consisting of" excludes any element, step,
or ingredient not specified in the claim element. As used herein,
"consisting essentially of" does not exclude materials or steps
that do not materially affect the basic and novel characteristics
of the claim. In each instance herein any of the terms
"comprising", "consisting essentially of" and "consisting of" may
be replaced with either of the other two terms. The invention
illustratively described herein suitably may be practiced in the
absence of any element or elements, limitation or limitations which
is not specifically disclosed herein.
[0102] One of ordinary skill in the art will appreciate that
starting materials, reagents, synthetic methods, purification
methods, analytical methods, assay methods, methods for coating,
methods for preparation of thin films, methods for preparation of
devices, device configurations and methods for testing device
configurations other than those specifically exemplified can be
employed in the practice of the invention without resort to undue
experimentation. All art-known functional equivalents, of any such
materials and methods are intended to be included in this
invention. The terms and expressions which have been employed are
used as terms of description and not of limitation, and there is no
intention that in the use of such terms and expressions of
excluding any equivalents of the features shown and described or
portions thereof, but it is recognized that various modifications
are possible within the scope of the invention claimed. Thus, it
should be understood that although the present invention has been
specifically disclosed by preferred embodiments and optional
features, modification and variation of the concepts herein
disclosed may be resorted to by those skilled in the art, and that
such modifications and variations are considered to be within the
scope of this invention as defined by the appended claims.
[0103] All references cited herein are hereby incorporated by
reference to the extent that there is no inconsistency with the
disclosure of this specification. Some references provided herein
are incorporated by reference to provide details concerning sources
of starting materials, additional starting materials, additional
reagents, additional methods of synthesis, additional methods of
analysis, device configurations, methods for use of devices and
additional uses of the invention. ##STR1## ##STR2## ##STR3##
EXAMPLES
Example 1
Synthesis of Poly(arylboranes)
[0104] Poly(arylborane)s were prepared in a two-step synthesis from
commercially available starting materials according as illustrated
in Scheme 3; first two different borane reagents were prepared with
a mesityl or tripyl group (step A), then the borane reagent was
polymerized with an aromatic dibromo compound after transforming it
into its Grignard reagent (step B). Representative syntheses are
given below.
[0105] Scheme 4 shows the structure of the polymers prepared in
this way, six with mesityl substituents on the boron atoms (x
series) and seven with tripyl substituents (y series). Seven
different dibromo-aromatic compounds were used as the starting
materials: 5,5'-dibromobithiophene (polymers 3a),
2,5-dibromo-3-hexyl-thiophene (polymers 3b),
1,4-dibromo-2,5-bis(decyloxy)benzene (polymers 3c),
9,9-dihexyl-2,7-dibromofluorene (polymers 3d),
9,9-didodecyl-2,7-dibromofluorene (polymers 3e),
2,5-dibromo-3-dodecyl-thiophene (polymers 3f), and
9,9-diisooctyl-2,7-dibromofluorene (polymers 3g). The structures of
all the intermediates and polymers were confirmed by .sup.1H-NMR
analysis. The occurrence of the coupling reaction (step 2) was
confirmed by the disappearance of the .sup.1H-NMR signal
corresponding to the methoxy protons of the borane reagent at 3.6
ppm. The .sup.1H-NMR spectra of some of the polymers showed the
presence of tetrahydrofuran (THF, the solvent used in the
polymerization) in about one molar equivalent with respect to boron
atoms suggesting that a significant fraction of the boron atoms of
the polymers are coordinated to a molecule of solvent. Gel
permeation chromatography results indicated that these materials
have a broad molecular weight distribution ranging from a few
repeat units to greater than 60 repeat units.
[0106] All of the prepared polymers were colored viscous oils with
the exception of 3ay and 3by which were colored powdery solids. The
polymers were at least partially soluble in THF and chloroform with
exception of polymer 3dx, which was insoluble in these solvents.
The fluorene derivatives 3dx, 3dy, 3ex, 3ey and 3gy were soluble in
toluene or ortho-xylene and the thiophene derivatives were soluble
in THF, acetonitrile and chloroform. All the prepared polymers were
found to be air stable for an extended period of time (at least
three months). ##STR4## TABLE-US-00001 Scheme 4: Structure and
properties of pi-conjugated organoboron polymers produced by the
methods in Examples 3 and 4. Structure Mesityl derivative (3?x)
Tripyl Derivative (3?y) ##STR5## Brown viscous oil Green
fluoroscence Brown powder Green fluorescence ##STR6## Brown viscous
oil Blue-green fluorescence Yellow-brown powder Green fluorescence
##STR7## Brown viscous oil Blue-green fluorescence Brown viscous
oil Blue-green fluorescence ##STR8## Yellow viscous oil Blue
fluorescence Yellow viscous oil Blue fluorescence ##STR9## Yellow
viscous oil Blue fluorescence Yellow viscous oil Blue fluorescence
##STR10## Brown viscous oil Blue-green fluorescence Brown viscous
oil Blue-green fluorescence ##STR11## Yellow viscous oil Blue
fluorescence
[0107] Elemental analysis data combined with .sup.1H-NMR data
confirmed that all the polymers with the exception of 3by contained
alternating aromatic and boron repeat units (i.e. had structure of
the type of Scheme 1, formula b) and that the aromatic unit
terminated the polymer at least on one side. Elemental analysis
indicated that polymer 3by contained an excess of sulfur indicating
that this polymer may contain short segments of homopolymerized
3-hexylthiophene (Scheme 1, formula h, with n equal to about 1 and
m equal to about 3).
[0108] The photoluminescence emission spectra were recorded for
each polymer using an excitation wavelength of 230 nm with a
Shimadzu RF-1501 Spectrofluorometer in chloroform, THF, cyclohexane
or dimethylsulfoxide (DMSO). The emission maxima in chloroform are
given in Table 1. The location of the emission maxima were
independent of the excitation wavelength, but showed a strong
dependence on solvent polarity. For instance, 3by exhibited a blue
shifted emission (lambda.sub.max=492 nm) in less polar THF and red
shifted emission in polar DMSO (lambda.sub.max 533 nm).
TABLE-US-00002 TABLE 1 Optical properties of organoboron polymers
in chloroform. Absorbance (.lamda..sub.max) Emission
(.lamda..sub.max) 3ax 330, 440 394, 774 3ay 455, 477 481 3bx 340
443 3by 240, 300, 402 337, 431, 672, 859 3cx 230, 360 302, 464 3cy
450, 479 465 3dx 230, 320 419, 791
Synthesis of the Borane Reagents (1x,y)
[0109] Dimethoxymesitylborane (1x): To a stirred solution of
magnesium turnings (3.11 g, 0.128 mol) and a crystal of iodine,
2-bromomesitylene (23.40 g, 0.118 mol) in THF (80 cm.sup.3) was
added dropwise at room temperature. The reaction was allowed to
reflux for 3 hours. After the reaction mixture was cooled, it was
added dropwise to an ether solution (80 cm.sup.3) of
trimethoxyborane (26 cm.sup.3, 0.229 mol) at -15.degree. C. The
reaction was stirred at -15.degree. C. for 3 hours, was warmed to
room temperature, and left to stir overnight. The solution was then
filtered under argon and the precipitated salts were washed with
dry pentane (20 cm.sup.3). The filtrates were combined,
concentrated and distilled under vacuum to give
dimethoxymesitylborane 1x. .sup.1H NMR (200 MHz, CDCl.sub.3) 2.28
ppm (s, 6H), 2.30 ppm (s, 3H), 3.58 ppm (s, 6H), 6.84 ppm (s,
2H).
Synthesis of Polymers (3a-3e) in THF
[0110] To a clean dry round bottom flask, the borane reagent 1 (2
mmol, 1 eq.), the commercially available aromatic dibromide 2 (2
mmol,1 eq.) and magnesium turnings (4 mmol, 2 eq.) were added to 15
cm.sup.3 of THF. The reaction was allowed to reflux for 24 to 72
hours depending on the substrates. Color change and
photoluminescence generally indicated the completion of the
reaction. The reaction was cooled to room temperature and a few
drops of methanol were added. The solvent was removed and the
obtained gum was dissolved in a minimal amount of chloroform and
then precipitated in methanol. The insoluble part was centrifuged
down and washed repeatedly with methanol. The solvent was removed
in vacuo.
Synthesis of polymers (3a-3e) in cyclohexane
[0111] To a stirred solution of the commercially available
dibromide 2 in anhydrous cyclohexane (dried over calcium hydride) 1
eq. of n-butyllithium (n-BuLi) and 1 eq. of
tetramethylethylenediamine (TMEDA) were added at -15.degree. C. The
mixture was warmed to room temperature for 15 minutes (to ensure
the formation of the lithio compound) and then cooled back to
-15.degree. C. A solution of the borane reagent 1 in cyclohexane
was added to the reaction mixture dropwise over 30 minutes. The
reaction was stirred at room temperature for 48 hours. Color change
and photoluminescence indicated the completion of the reaction.
Methanol (.about.10 cm.sup.3) was added to quench the reaction. The
solution was gravity filtered to remove all the precipitated salts.
The solvent was removed in vacuo. .sup.1H-NMR showed no methanol in
the sample, suggesting that the boron is free from
coordination.
Synthesis of 3f and 3g in THF via lithio compound
[0112] To a stirred solution of the commercially available aromatic
dibromide 2 in anhydrous THF was added 2 eq. of n-butyllithium
(n-BuLi) at -78.degree. C. The mixture was warmed to room
temperature for 15 minutes (to ensure the formation of the
di-lithiated compound) and then cooled back to .about.78.degree.
C.
[0113] A solution of the borane reagent 1 in THF was added to the
reaction mixture dropwise over 5 minutes. The reaction was stirred
at room temperature for 48 hours. Color change and
photoluminescence indicated the completion of the reaction.
Methanol (.about.10 cm.sup.3) was added to quench the reaction. The
solution was gravity filtered to remove all the precipitated salts.
The solvent was removed in vacuum. 3fx and 3fy were both brown gums
and had blue-green photoluminescence. 3gy was a yellow gum and had
blue photoluminescence.
Example 2
Synthesis of Poly(vinylborane)s
[0114] Poly(vinylborane)s were synthesized by reacting
trans-1,2-bis(tributyltin)ethene with dichloroboranes (Scheme 5).
.sup.1H-NMR and elemental analysis indicated that the desired
products were formed. ##STR12##
Synthesis of trans-1,2-bis(tributyltin)ethene
[0115] Tribuytyltin hydride (3.15 g, 10.8 mmol) and
ethynyltributylstannane (3.4 g 10.8 mmol) and a catalytic amount of
azobisisobutyronitrile (AIBN) were heated at 90.degree. C. for 10
hours under an inert argon atmosphere. The reaction was vacuum
distilled and the product was obtained in 95% yield.
Synthesis of Dichlorohexylborane
[0116] A solution of 1.91 g (16.25 mmol) of boron trichloride and
1.37 g (2.03 mL, 16.25 mmol) of 1-hexene in 5 cm.sup.3 of pentane
was stirred under argon at -78.degree. C. for 15 minutes.
Tributylsilane (3.26 g, 16.25 mmol) was added dropwise to the
stirred reaction mixture and left to stir overnight at room
temperature. Vacuum distillation yielded dichlorohexylborane in 90%
yield.
Synthesis of 3i and 3h
[0117] To a stirred solution of the
trans-1,2-bis(tributyltin)ethene in anhydrous THF was added 2 eq.
of n-butyllithium (n-BuLi) at -78.degree. C. The mixture was warmed
to room temperature for 15 minutes (to ensure the formation of the
di-lithiated compound) and then cooled back to -78.degree. C. A
solution of the dichloroborane reagent in THF was added to the
reaction mixture dropwise over 5 minutes. The reaction was stirred
at room temperature for 48 hours. Color change indicated the
completion of the reaction. Methanol (.about.10 cm.sup.3) was added
to quench the reaction. The solution was gravity filtered to remove
all the precipitated salts. The product was washed with chloroform
and the solvent was removed in vacuum.
Example 3
Electrochemical Doping
[0118] To identify the n-type semiconducting behavior of these
polymers, we cast thin films onto a platinum working electrode and
subjected these films to cyclic voltammetry. FIG. 1 shows the
reduction of the 3ay polymer under an argon atmosphere. N-type
behavior is generally indicated by a facile reduction process
(electron injection) of the film on the electrode surface. We
observe a reduction process in our materials, however, this reduced
or n-doped form of the material is unstable or highly soluble
because no film remains on the electrode after reducing the
film.
Example 4
Doping with Sodium Naphthalenide (NaNp)
[0119] To a solution of naphthalene (150 mg, 1.17 mmol) in
anhydrous THF (.about.40 cm.sup.3), was added sodium metal (30 mg,
1.3 mmol) at room temperature under an argon atmosphere. The
mixture was allowed to stir for 2 hours. The resulting dark green
solution was added dropwise via cannula to the stirred polymer in
THF. The solution was allowed to stir for 30 minutes at room
temperature.
[0120] The polymers 3cy, 3dx, 3ex, and 3ey dramatically changed
color upon adding sodium naphthalenide from a pale yellow to a dark
purple-black or greenish-black color and lost their characteristic
photoluminescence, indicating that reduction of the polymers has
occurred, presumably by formation of a radical anion. Upon exposing
the polymers to air (even in trace amounts) the polymers returned
to their original colors and regained their photoluminescence,
confirming that the reduction is a reversible process, i.e. that
this is effectively a doping process and not an irreversible
chemical reduction of the polymer chain.
Example 5
Device Fabrication and Testing
[0121] Poly(bithienyl-tripylborane) (polymer 3ay) was used for the
fabrication of OLED prototypes. The device design is shown in FIG.
2C and comprises a layer of patterned ITO as the anode, a thin film
of PEDOT/PSS as the hole injecting layer, our pi-conjugated
organoboron polymer, and an aluminum cathode. The devices were
fabricated using a clean room facility. ITO was patterned according
to well-known photolithographic masking and etching methods. A 50
nm layer of PEDOT/PSS was spin coated at 2000 RPM from a freshly
filtered commercially available solution of this material (Baytron
P, electronic grade VP Al 4083, H. C. Starck) as a hole injection
layer. After annealing at 100 C for 30 minutes, a 200 nm layer of
the pi-conjugated organoboron polymer was spin coated at 2000 RPM
from freshly filtered chloroform solution. To complete the devices,
a top layer of aluminum was deposited by thermal vapor deposition
on top of the organoboron polymer. The operation and light output
of devices of were tested by application of a supplied voltage and
evaluated by visual inspection. The anode and cathode were
connected to the outputs of a 30 V DC power supply. The voltage
between the anode and cathode was increased manually until there
was an observed output of light. The voltage at which this occurred
was recorded at 6-7 V for a number of devices tested. The color of
the light output was yellow-green light. The turn-on voltage of
this un-optimized device in air was around 6-7 Volts. Those skilled
in the art know that device optimization will result in a decrease
of the turn-on voltage. As known in the art, quantification of the
light output and lifetime of the device can be readily measured
employing art known techniques, and standard instrumentation such
as a direct current (DC) source coupled to a metering device, a
photodiode, a photomultiplier, an integration sphere and laboratory
software. Complete OLED/PLED test systems are now commercially
available (for example the Eclipse test system from Cambridge
Display technologies, LTD.http//www.cdtltd.co.uk/).
Example 6
Device Fabrication and Testing
[0122] To test the electron transport properties of these materials
we constructed a diode with the structure illustrated in FIG. 2D,
using a known light emitting polymer,
poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene)
(MEH-PPV). The device structure consisted of glass\ITO\Baytron
P\MEH-PPV\organoboron polymer 3by\aluminum. The current-voltage
characteristics of these devices were monitored and light output
was visually confirmed. FIG. 3 shows the current versus voltage
data obtained for a device containing a ca. 100 nm thick 3by
ETL.
Example 7
Synthesis of Poly(thiazole-mesitylborane) by reaction of
dibromothiazole and 1x (Scheme 3) in THF
[0123] To a clean dry round bottom flask, the borane reagent 1x
(8.2 mmol, 1 eq.), the commercially available aromatic dibromide,
2,5-dibromothiazole (8.2 mmol,1 eq.) and magnesium turnings (16.4
mmol, 2 eq.) were added to 24 cm.sup.3 of anhydrous THF. The
reaction was allowed to reflux under an inert atmosphere for 72
hours. Color change and polymer precipitation generally indicated
the completion of the reaction. The reaction was cooled to room
temperature and a few drops of methanol were added. The solvent was
removed and the brown polymer obtained was dissolved in a minimal
amount of N,N-dimethylformamide and then precipitated in methanol.
The insoluble precipitate was centrifuged down and washed
repeatedly with methanol. The solvent was removed in vacuo to
provide the poly(thiazole-mesitylborane).
* * * * *