U.S. patent application number 10/847525 was filed with the patent office on 2004-11-25 for blend of viscosity modifier and luminescent compound.
Invention is credited to Kram, Shari L., Marshall, William B., O'Brien, James J., Pickering, Todd A., Wu, Weishi.
Application Number | 20040232385 10/847525 |
Document ID | / |
Family ID | 33490496 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040232385 |
Kind Code |
A1 |
Kram, Shari L. ; et
al. |
November 25, 2004 |
Blend of viscosity modifier and luminescent compound
Abstract
The present invention relates to a composition comprising a
blend of a luminescent polymer and a low molecular weight (<5000
amu) viscosity modifier, which has an emission maximum in the range
of 350-480 nm, contains no exocyclic double bonds, and modifies the
viscosity of the polymer without substantially altering emissive
properties of the neat polymer. Modification of viscosity without
concomitant modification of emissive properties is desirable where
the polymer is already tuned to emit at the desired wavelength.
Inventors: |
Kram, Shari L.; (Midland,
MI) ; Marshall, William B.; (Midland, MI) ;
O'Brien, James J.; (Midland, MI) ; Pickering, Todd
A.; (Midland, MI) ; Wu, Weishi; (Midland,
MI) |
Correspondence
Address: |
THE DOW CHEMICAL COMPANY
INTELLECTUAL PROPERTY SECTION
P. O. BOX 1967
MIDLAND
MI
48641-1967
US
|
Family ID: |
33490496 |
Appl. No.: |
10/847525 |
Filed: |
May 17, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60472288 |
May 21, 2003 |
|
|
|
Current U.S.
Class: |
252/301.16 |
Current CPC
Class: |
C09K 11/06 20130101;
H01L 51/0058 20130101; H01L 51/0052 20130101; C09K 2211/1416
20130101; C08L 65/00 20130101; Y10S 428/917 20130101; H01L 51/0039
20130101 |
Class at
Publication: |
252/301.16 |
International
Class: |
C09K 011/06 |
Claims
What is claimed is:
1. A composition comprising a blend of a) a luminescent polymer
having a weight average molecular weight (M.sub.w) of at least
20,000 and b) a viscosity modifier that 1) is a solid at room
temperature; 2) has a M.sub.w of less than 5000; 3) has a
luminescent emission maximum of 350 to 480 nm; 4) does not
substantially diminish charge transporting properties of the
combination of the modifier and the polymer; and 5) contains no
exocyclic conjugated double bonds; wherein the modifier and its
concentration in the blend are selected so that the blend exhibits
a luminescent emission maximum that is within 20 nm of the
luminescent emission maximum of the polymer alone.
2. The composition of claim 1 wherein the viscosity modifier does
not contain any O, N, or S atoms with delocalized unshared pairs of
electrons.
3. The composition of claim 1 which further includes a solvent for
the luminescent polymer and the viscosity modifier.
4. The composition of claim 3 wherein the solvent is selected from
the group consisting of toluene, cyclohexylbenzene, xylenes,
mesitylene, tetralin, decalin, methyl benzoate, isopropyl biphenyl,
and anisole, and combinations thereof.
5. The composition of claim 1 wherein the luminescent emission
maximum of the blend is within 10 nm of the luminescent emission
maximum of the polymer.
6. The composition of claim 5 wherein the luminescent emission
maximum of the blend is within 5 nm of the luminescent emission
maximum of the polymer.
7. The composition of claim 1 wherein the viscosity modifier is a
fluorene oligomer.
8. The composition of claim 1 wherein the viscosity modifier is
selected from the group consisting of mono-, bis-, and
tris-9,9-disubstituted fluorenes; fluorenylidenes, and
trifluorenylbenzenes.
9. The composition of claim 8 wherein the viscosity modifier is
selected from the group consisting of
1,2,4-tris(9,9-bisbutylfluorene)benzene and
1,3,5-tris(9,9-bisbutylfluorene)benzene.
10. The composition of claim 1 wherein the polymer contains
structural units of monomers selected from the group consisting of
9,9-disubstitutedfluorene,
2-methoxyl-5-(2'-ethylhexyl)phenylenevinylene; 2,5-dioctyloxy-
1,4-phenylenevinylene; 2-silyl- 1,4-phenylenevinylene; 2,5-disilyl-
1,4-phenylenevinylene; 3-alkylthiophene; 2,5-dialkyl-
1,4-phenylenevinylene; 2,5-dialkoxyphenylene; 2,5-dialkylphenylene;
and N-vinylcarbazole.
11. The composition of claim 1 wherein the polymer contains
structural units of a first monomer selected from the group
consisting of 9,9-dialkylfluorene, 9,9-diarylfluorene, and
9,9-aralkylfluorene, and a second monomer selected from the group
consisting of substituted and unsubstituted thiophenes,
dithiophenes, benzodiathiazoles, oxazoles, oxadiazoles,
benzoxazoles, dibenzofurans, benzothiophenes, dibenzothiophenes,
dibenzosiloles, benzidines, diarylamines, triarylamines, benzenes,
biphenylenes, naphthalenes, anthracenes, phenanthrenes, styrenes,
quinolines, and stilbenes.
12. A composition comprising a blend of a) a luminescent polymer
having a weight average molecular weight (M.sub.w) of at least
20,000 and b) a viscosity modifier that 1) is a solid at room
temperature; 2) has a M.sub.w, of less than 5000; 3) has a
luminescent emission maximum of from 350 to 480 nm; 4) does not
substantially diminish charge transporting properties of the
combination of the modifier and the polymer; and 5) contains no
exocyclic conjugated double bonds; and c) a solvent for the
luminescent polymer and the viscosity modifier; wherein the
relative amounts of the modifier and the polymeric compound in the
blend are such that the blend exhibits a luminescent emission
maximum that is within 10 nm of the luminescent emission maximum of
the polymer alone.
13. The composition of claim 12 wherein the luminescent polymer
includes structural units of a 9,9-disubstituted fluorene and a
monomer selected from the group consisting of benzidines
dithiophenes, and benzothiadiazoles.
14. The composition of claim 13 wherein the solvent is selected
from the group consisting of toluene, cyclohexylbenzene, xylenes,
mesitylene, tetralin, decalin, methyl benzoate, isopropyl biphenyl,
and anisole.
15. The composition of claim 14 wherein the structural units of a
9,9-disubstituted fluorene include substituents at the 9,9-position
are selected from the group consisting of C.sub.4-C.sub.12 alkyl,
C.sub.4-C.sub.12-alkoxy, substituted phenyl, unsubstituted phenyl,
substituted biphenyl, and unsubstituted biphenyl.
Description
CROSS-REFERENCE STATEMENT
[0001] This application claims the benefit of U.S. Provisional
application No. 60/472,288 filed March 21, 2003.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a blend of a viscosity
modifier and a luminescent compound.
[0003] Luminescent polymers find use in a number of applications
including roll-to-roll, screen, and ink jet printing; spin, dip,
and spray coating; and "doctor blading." While all of these
applications may require materials that emit at particular
wavelengths, they often widely differ in their viscosity
requirements. Thus, an emitting luminescent polymer that is useful
in both roll-to-roll and ink jet applications may require a high
viscosity (100 cps) for the former application and a relatively low
viscosity for the latter (about 10 cps).
[0004] Viscosity modification of luminescent polymers is known. For
example, in U.S. Pat. No. 6,372,154, Li describes the use of low
molecular weight functional additives to adjust the viscosity of
luminescent inks (L-inks) that contain viscous luminescent
polymers. These functional additives are described as possessing
electron-transporting properties or hole-transporting properties
that can be used to modify the charge transporting abilities of the
L-ink in addition to viscosity modification. However, it may be
desirable to modify the viscosity of luminescent polymers without
changing charge transporting properties, which may adversely affect
light-emitting properties. Thus, if the luminescent polymer
inherently emits at a desired wavelength, it would be
disadvantageous to use a modifier that reduces viscosity but
concomitantly shifts the luminescent emission maximum of the blend
to a wavelength substantially different from the optimal
wavelength. Accordingly, it would be advantageous in the art of
viscosity modification of luminescent polymers to discover
modifiers that allow tuning of viscosity without substantially
altering emissive properties of the neat polymer.
SUMMARY OF THE INVENTION
[0005] The present invention addresses the deficiencies in the art
by providing a composition comprising a blend of a) a luminescent
polymer having a weight average molecular weight (M.sub.w) of at
least 20,000 and b) a viscosity modifier that 1) is a solid at room
temperature; 2) has a M.sub.w of less than 5000; 3) has a
luminescent emission maximum in the range of 356 to 480 nm; and 4)
does not substantially diminish charge transporting properties of
the combination of the modifier and the polymer; and 5) contains no
exocyclic conjugated double bonds; wherein the modifier and its
concentration in the blend are selected so that the blend exhibits
a luminescent emission maximum that is within 20 nm of the
luminescent emission maximum of the polymer alone.
[0006] The blend of the claimed invention provides a way to tune
viscosity without substantially altering the luminescent emission
maximum of the neat polymer. This effect is particularly
advantageous where the neat polymer already possesses optimal
luminescent emissive properties.
DETAILED DESCRIPTION OF THE INVENTION
[0007] The present invention is a composition that is a blend of a
luminescent polymer and a viscosity modifier. The luminescent
polymer can be any polymer that is luminescent under UV radiation
or under a suitable electric field bias. Preferably, the polymer is
luminescent under an electric field bias, that is, it is
electroluminescent. Examples of luminescent polymers include those
that contain structural units of: 9,9-disubstituted fluorenes
including 9,9-dialkylfluorenes, 9,9-diarylfluorenes, and
9,9-aralkylfluorenes; 9-substituted fluorenes such as
spirofluorenes; phenylenes including 2,5-dialkoxyphenylene and
2,5-dialkylphenylene; phenylenevinylenes including
2-methoxyl-5-(2'-ethylhexyl)phenylenevinylene,
2,5-dioctyloxy-1,4-phenyle- nevinylene,
2-silyl-1,4-phenylenevinylene, 2,5-disilyl-1,4-phenylenevinyle- ne
and 2,5-dialkyl-1,4-phenylenevinylene; thiophenes;
3-alkylthiophenes; thiophenevinylenes; pyrroles; acetylenes;
diacetylenes; aniline; N-vinylcarbazole, and combinations thereof.
As used herein, the term, "structural unit" refers to the remnant
of the compound after it undergoes polymerization. Thus, a
structural unit of a trans-acetylene is represented by the
following structure: 1
[0008] Preferred luminescent polymers contain structural units of a
9,9-disubstituted fluorene that is polymerized through the 2 and 7
carbon atoms, which structural unit is represented by the following
structure: 2
[0009] structural unit of 9,9-disubstituted fluorene where each R
is independently alkyl, alkoxy, aryl, aryloxy, or aralkyl;
preferably, C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20-alkoxy,
substituted or unsubstituted phenyl, biphenyl, naphthalenyl,
anthryl, phenanthryl, thienyl, or furanyl; and more preferably
C.sub.4-C.sub.12 alkyl, C.sub.4-C.sub.12-alkoxy, or substituted or
unsubstituted phenyl or biphenyl.
[0010] The electroluminescent polymer more preferably contains
structural units of a 9,9-disubstituted fluorene and structural
units of at least one other comonomer. Examples of polymers
containing structural units of a 9,9-disubstituted fluorene and
other comonomers can be found in U.S. Pat. Nos. 5,708,130;
5,777,070; 6,169,163; and 6,363,083, which teachings are
incorporated herein by reference.
[0011] Examples of suitable comonomers include polymerizable
substituted and unsubstituted thiophenes, dithiophenes,
benzodiathiazoles, oxazoles, oxadiazoles, benzoxazoles,
dibenzofurans, benzothiophenes, dibenzothiophenes, dibenzosiloles,
benzidines including N,N,N'N'-tetraarylbenzidines, diarylamines,
triarylamines, benzenes, biphenylenes, naphthalenes, anthracenes,
phenanthrenes, styrenes, quinolines, and stilbenes. More preferred
comonomers include benzidines, dithiophenes, and
benzothiadiazoles.
[0012] The viscosity modifier that is used to make the blend is
solid at room temperature. It has a weight average molecular weight
(M.sub.w) of less than 5000, preferably less than 2000 and a
polydispersity of preferably less than 1.2, more preferably less
than 1.1, most preferably 1.0. The luminescent emission maximum of
the modifier is not greater than 480 nm and not less than 350 nm,
more preferably not less than 400 nm. Consequently, the modifier
has a wider band gap between the highest occupied molecular orbital
(HOMO) and the lowest unoccupied molecular orbital (LUMO) than that
of the emitting chromophore of the electroluminescent polymer. It
is believed that this comparatively wide modifier band gap results
in a substantial absence of shifting of luminescent emission
maximum of the blend as compared to the polymer.
[0013] The modifier is selected so as not to substantially diminish
charge transporting properties of the combination of the modifier
and the polymer because such modifiers tend to adversely affect the
efficiency of the luminescent material. Examples of modifiers with
such an adverse tendency are those that contain heteroatoms with
delocalized unshared pairs of electrons such as N, O, and S atoms
with delocalized unshared pairs of electrons. Thus,
di-naphthalene-1-y1-diphenyl-biphenyl-4,4'-diam- ine (.alpha.-NPA),
which contains two nitrogen atoms with delocalized unshared pairs
of electrons, would not be a suitable modifier for the luminescent
polymer.
[0014] The modifier is also selected so as not to contain
exocyclic, that is, it contains no non-aromatic, conjugated double
bonds because such compounds tend to oxidize readily. Thus,
1,1,4,4-tetraphenyl- 1,3-butadiene (TPB) would also not be a
suitable modifier for the luminescent compound.
[0015] Furthermore, the selection of modifier and its concentration
in the blend are such that the blend exhibits a luminescent
emission maximum that is within 20 nm, preferably within 10 nm,
more preferably within 5 nm, and most preferably within 1 nm of the
luminescent emission maximum of the polymer alone. Preferably, the
weight percent concentration of the modifier based on the weight of
the modifier and the luminescent polymer is at least 1 weight
percent, more preferably at least 5 weight percent, and most
preferably at least 10 weight percent; and preferably less than 60
weight percent, more preferably less than 50 weight percent, and
most preferably less than 30 weight percent.
[0016] Examples of preferred modifiers are substituted and
unsubstituted fluorene and blends thereof; fluorene oligomers such
as mono-, bis-, and tris-9,9-disubstituted fluorenes and blends
thereof; fluorenylidenes and blends thereof, and
trifluorenylbenzenes and blends thereof. An example of a
tris-9,9-disubstituted fluorene is illustrated by the following
structure: 3
[0017] where R is previously defined.
[0018] The tris-9,9-disubstituted fluorene can be prepared, for
example, by a Suzuki coupling reaction as shown: 4
[0019] Similarly, trifluorenylbenzenes can prepared by reacting a
tribromobenzene with the
2-(1,3,2-dioxaborloan-2-y1)-9,9-dibutylfluorene. Preferred
trifluorenylbenzenes include 1,3,5-tri(9,9-disubstitutedfluoren-
yl)benzene, where R is previously defined.
[0020] An example of a bifluorenyl-substituted bifluorenylidene is
illustrated by the following structure: 5
[0021] where R is previously defined. This bifluorenylidene can be
prepared as illustrated by the following reaction sequence: 6
[0022] where R is as previously defined, preferably each R is
independently C.sub.4-C.sub.12-alkyl, more preferably
C.sub.4-C.sub.8-alkyl.
[0023] The luminescent polymer and the viscosity modifier are
advantageously combined with a sufficient amount of solvent to make
an ink. The amount of solvent varies depending upon the solvent
itself and the application, but is generally used at a
concentration of at least 80 weight percent, more preferably at
least 90 weight percent, and most preferably at least 95 weight
percent, based on the weight of the luminescent polymer, the
modifier, and the solvent.
[0024] Examples of suitable solvents for the polymer and the
modifier include benzene; mono-, di- and trialkylbenzenes including
xylenes, mesitylene, toluene, n-propylbenzene, n-butylbenzene,
n-pentylbenzene, n-hexylbenzene, cyclohexylbenzene, diethylbenzene,
dodecylbenzene, and n-pentylbenzene; furans including
tetrahydrofuran and 2,3-benzofuran; tetralin
(tetrahydronaphthalene); cumene; cis-and trans-decalin
(decahydronaphthalene); durene; chloroform; limonene;
alkoxybenzenes including anisole, and methyl anisoles; alkyl
benzoates including methyl benzoate; biphenyls including isopropyl
biphenyl; pyrrolidinones including cyclohexylpyrrolidinone;
imidazoles including dimethylimidazolinone; and combinations
thereof. More preferred solvents include toluene,
cyclohexylbenzene, xylenes, mesitylene, tetralin, methyl benzoate,
isopropyl biphenyl, and anisole, and combinations thereof.
[0025] In a typical application, the ink formulation can be
deposited on a substrate such as indium-tin-oxide (ITO) glass
having a hole transporting material disposed thereon. The solvent
is then evaporated, whereupon the ink forms a thin amorphous film
of the viscosity modified luminescent polymer. Significantly, the
presence of the viscosity modifier provides a way to tune viscosity
without affecting the critical property of film thickness. The film
is used as an active layer in an organic light-emitting diode
(OLED), which can be used to make self-emissive flat panel
displays.
[0026] The following examples are for illustrative purposes only
and is not intended to limit the scope of the invention.
EXAMPLES 1-4
Preparation of Formulation of a Viscosity Modified Polymer
A. Preparation of 1,3,5-Tris(9,9-dibutylfluorenyl)benzene
[0027] 1,3,5-Tribromobenzene (3.12 g, 9.92 mmol),
2-(1,3,2-dioxaborloan-2-- y1)-9,9-dibutylfluorene (12.10 g 34.72
mmol), and Aliquat 336 (1.5 g) were dissolved in 125 mL of toluene
and added to a 250-mL 3-necked flask equipped with an overhead
stirrer and a reflux condenser connected to a nitrogen line. An
aqueous Na.sub.2CO.sub.3 solution (2M, 30 mL) was added to the
mixture and the flask was purged with nitrogen for 10 minutes.
Pd(PPh.sub.3).sub.4 (0.2 g, 0.5 mol %) was added to the mixture,
which was then heated to 95.degree. C. with stirring overnight. A
solution of diethyldithiocarbamic acid sodium salt trihydrate (5%,
200 mL) was added and the mixture was heated at 80.degree. C. for
16 hours. The aqueous layer was removed and the organic layer was
washed with warm, dilute acteic acid solution (2%, 3.times.300 mL)
followed by warm water (1.times.300 mL), and finally dried with
MgSO.sub.4. The toluene was removed in vacuo to yield the crude
product, which was purified by column chromatography on silica gel
with hexanes/methylene chloride as eluent to yield 7 g (78%) of
1,3,5- tris(9,9-dibutylfluorenyl)benzene as a white solid. HPLC
showed that the product was >99% pure. The 1,2,4-
tris(9,9-dibutylfluorenyl)benzene isomer was made essentially as
described above except that 1,2,4-tribromobenzene was used as a
starting material instead of the 1,3,5 isomer. Each of these
isomers was used as a viscosity modifier as described in Part
B.
B. Preparation of the Ink Formulation
[0028] The electroluminescent polymer, viscosity modifier and
solvent are combined in a single vessel and mixed to obtain a
homogeneous solution or ink. The following Table shows the
concentration of the polymer and the modifier in the solvent. In
each case, the solvent is a mixture of xylene isomers and
ethylbenzene (obtained by J. T. Baker as VLSI grade mixed xylenes
and analyzed as m-xylene, 40-65%; o-xylene, 15-20%; p-xylene
<20%; ethyl benzene, 15-25%) at 98% wt/wt based on the total
weight of the solvent, the polymer, and the modifier. Polymer 1304
refers to LUMATION* 1304 green light emitting polymer (a trademark
of The Dow Chemical Company) and polymer 1100 refers to LUMATION*
1100 red light emitting polymer, both available from The Dow
Chemical Company. VMI refers to
1,2,4-tris(9,9-dibutylfluorenylbenzene) and VM2 refers to
1,3,5-tris(9,9-dibutylfluorenylbenzene). Examples 1 and 4 are
comparative examples and, therefore, not within the scope of the
blend of the present invention. These comparative examples are
included to demonstrate that the viscosity modifier does not
substantially alter the wavelength emission maximum of the blend as
compared to that of the pure polymer. Furthermore, the data
indicate that presence of the modifier enhances the efficiency of
the device.
1TABLE Polymer Viscosity Solution EL Device (wt/ Modifier Viscosity
Emission Efficiency @ Example # wt %) (wt/wt %) (cPs) max (nm) 1000
Cd/m.sup.2 1 (comp. 1304 none (0%) 16.02 536 6.34 ex.) (2%) 2 1304
VM1 (0.5%) 8.78 532 6.68 (1.5%) 3 1304 VM1 (1%) 4.18 532 6.82 (1%)
4 (comp. 1100 none (0%) 644 0.738 ex.) (2%) 5 1100 VM2 (1%) 640
0.790 (1%)
* * * * *