U.S. patent application number 10/169692 was filed with the patent office on 2003-10-02 for luminescent polymer.
Invention is credited to O'Dell, Richard, Towns, Carl.
Application Number | 20030186079 10/169692 |
Document ID | / |
Family ID | 28456004 |
Filed Date | 2003-10-02 |
United States Patent
Application |
20030186079 |
Kind Code |
A1 |
Towns, Carl ; et
al. |
October 2, 2003 |
Luminescent polymer
Abstract
A luminescent polymer comprising a triarylene repeat unit which
comprises a triarylene of general formula (I) which is substituted
or unsubstituted and an arylene repeat unit -[-Ar-]- that is
different from the triarylene repeat unit wherein X, Y and Z are
each independently O, S, CR.sub.2, SiR.sub.2 or NR and each R is
independently alkyl, aryl or H.
Inventors: |
Towns, Carl; (Essex, GB)
; O'Dell, Richard; (Jettenstetten, GB) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Family ID: |
28456004 |
Appl. No.: |
10/169692 |
Filed: |
November 7, 2002 |
PCT Filed: |
January 4, 2001 |
PCT NO: |
PCT/GB01/00019 |
Current U.S.
Class: |
428/690 ;
252/301.16; 252/301.35; 257/103; 257/40; 313/504; 313/506; 428/917;
526/256; 526/257; 526/258; 526/266; 526/279; 528/10; 528/377;
528/394; 528/423; 528/425 |
Current CPC
Class: |
C09K 2211/1458 20130101;
C08G 61/122 20130101; H01L 51/0059 20130101; C08G 61/12 20130101;
Y10T 428/31855 20150401; C08G 61/124 20130101; C08G 61/126
20130101; Y02E 10/549 20130101; C08G 61/10 20130101; C08G 61/125
20130101; C09K 2211/1433 20130101; H01L 51/0036 20130101; H01L
51/0043 20130101; H01L 51/50 20130101; C09K 2211/1416 20130101;
C08G 73/026 20130101; C09K 11/06 20130101; H01L 51/0035 20130101;
C08G 61/02 20130101; C09K 2211/1425 20130101; H01L 51/0039
20130101; C09K 2211/1483 20130101; C08G 61/123 20130101 |
Class at
Publication: |
428/690 ;
428/917; 313/504; 313/506; 257/40; 257/103; 252/301.16; 252/301.35;
526/256; 526/257; 526/258; 526/266; 526/279; 528/394; 528/423;
528/425; 528/377; 528/10 |
International
Class: |
H05B 033/14; C09K
011/06; C08G 061/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 2000 |
GB |
0000091.9 |
Feb 25, 2000 |
GB |
0004542.7 |
Mar 13, 2000 |
WO |
PCT/GB00/00911 |
Claims
1. A luminescent polymer comprising a triarylene repeat unit which
comprises a triarylene of general formula I which is substituted or
unsubstituted and an arylene repeat unit Ar that is different from
the triarylene repeat unit: 15wherein X, Y and Z are each
independently O, S, CR.sub.2, SiR.sub.2 or NR and each R is
independently alkyl, aryl or H.
2. A luminescent polymer according to claim 1, excluding the
polymer comprising a triarylene repeat unit which is an
unsubstituted triarylene of formula: 16
3. A luminescent polymer according to claim 1 or claim 2, which
comprises repeat units of the general formula II: triarylene repeat
unit--Ar (II)
4. A luminescent polymer according to claim 3, which comprises
repeat units having the general formula III which is substituted or
unsubstituted: 17where X, Y and Z are as defined in claim 1.
5. A polymer according to any one of the preceding claims, wherein
the triarylene repeat unit comprises a unit having the general
formula IV: 18wherein at least one of R.sup.1 to R.sup.6 comprises
an alkyl, aryl, heteroaryl, alkylaryl, arylalkyl, CN or halide
substituent.
6. A polymer according to any one of the preceding claims, wherein
X, Y and Z are each independently O or S.
7. A polymer according to claim 6, wherein X, Y and Z are each
S.
8. A polymer according to any one of the preceding claims wherein
Ar comprises a 2,7-linked 9,9 dialkyl fluorene, a 2,7-linked 9,9
diaryl fluorene, a p-linked dialkyl phenylene, a p-linked dialkoxy
phenylene, a phenylene vinylene, a 2,5-linked benzothiadiazole, a
2,5-linked alkyl benzothiadiazole, a 2,5-linked dialkyl
benzothiadiazole, a 2,5-linked substituted or unsubstituted
thiophene, a triarylamine or a bis triarylamine.
9. A polymer according to claim 8, wherein Ar comprises a
2,7-linked 9,9 dioctyl fluorene.
10. A polymer according to any one of the preceding claims, which
further comprises a further repeat unit of general formula V:
19which repeat unit is substituted or unsubstituted, wherein Q is
O, S, CR.sub.2, SiR.sub.2 or NR
11. A polymer according to claim 10, wherein Q is O or S.
12. A polymer according to claim 11, wherein Q is S.
13. A polymer according to any one of the preceding claims, the
degree of polymerisation of which is sufficient to achieve bandgap
convergence.
14. A polymer according to claim 13, wherein the degree of
polymerisation is at least 4.
15. An optical device or a component therefore, which comprises a
substrate and a composition comprising a polymer according to any
one of claims 1 to 14, supported on the substrate.
16. An optical device or a component therefore, according to claim
15, wherein the optical device comprises an electroluminescent
device.
17. An optical device according to claim 16, wherein the
electroluminescent device comprises: a first charge carrier
injecting layer for injecting positive charge carriers; a second
charge carrier injecting layer for injecting negative charge
carriers; a light-emissive layer (i) located between the charge
carrier injecting layers for accepting and combining positive and
negative charge carriers to generate light and (ii) comprising a
polymer according to any one of claims 1 to 13.
18. An optical device according to claim 17 further comprising a
material for transporting negative charge carriers that is located
either between the second charge carrier injecting layer and the
light-emissive layer or in the light-emissive layer.
19. An optical device according to claim 17 or 18 further
comprising a material for transporting positive charge carriers
that is located either between the first charge carrier injecting
layer and the light-emissive layer or in the light-emissive
layer.
20. An optical device according to any one of claims 17 to 19
wherein the light-emissive layer comprises a mixture comprising the
luminescent polymer according to any one of claims 1 to 14 and two
further polymers that are different from the luminescent
polymer.
21. An optical device according to claim 20 where the two further
polymers are for transporting negative charge carriers and/or
transporting positive charge carriers.
22. An optical device according to claim 20 or 21 where the mixture
comprises: 20where n.gtoreq.4, 0.05.ltoreq.x+z.ltoreq.0.5 and
0.5.ltoreq.y and x+y+z=1. 21where x+y=1, 0.5.ltoreq.x and
y.ltoreq.0.5 and n.gtoreq.2. 22where w+x+y=1, w.gtoreq.0.5,
0.ltoreq.x+y.ltoreq.0.5 and n.gtoreq.2.
23. Use of a polymer according to any one of claims 1 to 14, as a
component of an optical device.
24. Use according to claim 23, wherein the optical device comprises
an electroluminescent device.
25. A composition comprising a mixture comprising a luminescent
polymer according to any one of claims 1 to 14, and a material for
transporting positive charge carriers.
26. A composition according to claim 25 further comprising a
material for transporting negative charge carriers.
27. A composition according to claim 25 or claim 26, wherein the
luminescent polymer according to any one of claims 1 to 14
comprises a triarylene repeat unit which is an unsubstituted or
substituted triarylene of formula: 23
Description
[0001] The present invention relates to a novel luminescent
polymer, especially for use in an optical device such as an optical
device comprising an electroluminescent device.
[0002] Electroluminescent devices are structures which emit light
when subject to an applied electric field. In its simplest form, an
electroluminescent device comprises a light-emissive layer between
two electrodes. The cathode electrode injects negative charge
carriers (electrons) and the anode electrode injects positive
charge carriers (holes) into the light-emissive layer. Light
emission occurs when the electrons and holes combine in the
light-emissive layer to generate photons. As a practical aspect,
one of the electrodes is typically transparent, to allow the
photons to escape the device. The light-emissive layer should be
made from a light-emissive material which may be laid down as a
film without substantially affecting the luminescent
characteristics of the material and which is stable at the
operational temperature of the device.
[0003] Organic electroluminescent devices which use an organic
material as the light-emissive material are known in this art.
Among organic materials, simple aromatic molecules such as
anthracene, perylene and coronene are known to show
electroluminescence. U.S. Pat. No. 4,539,507 discloses the use of
small molecule organic materials as the light-emissive material,
such as 8-hydroxy quinoline(aluminium)"Alq". PCT/WO90/13148
discloses an electroluminescent device comprising a semiconducting
layer comprising a polymer film as the light-emissive layer which
comprises at least one conjugated polymer. In this case, the
polymer film comprises a poly(para-phenylenevinylene)(PPV)
film.
[0004] The colour of the light generated by the light-emissive
material is determined by the optical gap or bandgap of the organic
light-emissive materials, that is to say the difference in energy
levels between the "highest occupied molecular orbital" ("HOMO")
and the "lowest unoccupied molecular orbital" ("LUMO") levels.
Effectively, the bandgap is the energy difference between the
valence and conduction bands. These levels can be estimated by
photoemission measurements and measurements of the electrochemical
potentials for oxidation and reduction. The level of these energies
is affected by numerous factors. Accordingly, the use of such
values is indicative rather than quantitative.
[0005] It is known to use a semiconductive conjugated copolymer as
the light-emissive layer in an electroluminescent device. The
semiconductive conjugated copolymer comprises at least two
chemically different monomer units which, when existing in their
individual homopolymer forms, typically have different
semiconductor bandgaps. The proportion of the chemically different
monomer units in the copolymer can be selected to control the
semiconductor bandgap of the copolymer so as to control the optical
properties of the copolymer. To some degree, the extent of
conjugation of the copolymer can be said to affect the .pi.-.pi.*
bandgap of the copolymer. Increasing the extent of conjugation has
the effect of decreasing the bandgap up to the point of bandgap
convergence. Therefore, selection of appropriate reaction
components may be used to modulate the bandgap. This property may
be exploited so that the semiconductor bandgap is modulated to
control the wavelength (i.e. colour) of radiation emitted during
luminescence. This gives the very desirable feature of controlling
the colour of light output from the polymer. This property is
useful particularly in the construction of electroluminescent
devices.
[0006] EP 0686662 discloses a device for emitting green light. The
anode is a layer of transparent indium-tin oxide. The cathode is a
LiAl layer. Between the electrodes is a light-emissive layer of
PPV. The device comprises also a hole transport layer of
polyethylene dioxythiophene which provides an intermediate energy
level which aids the holes injected from the anode to reach the
HOMO level in the PPV.
[0007] "Efficient Blue-light Emitting Devices From Conjugated
Polymer Blends", Burgeson et al., Adv. Mater. 1996, 8, No. 12,
pages 982-985 describes a blue-light emitting device which employs
conjugated polymer blends. The emissive layer of the device
consists of a blend of PDHPT with PDPP. Light emission is from the
PDHPT alone.
[0008] Organic materials having smaller optical gaps, towards the
red end of the visible spectrum, are of particular interest at
present. It has been suggested that conjugated polymers that
possess narrow bandgaps are a current topic of interest because
such polymers will be useful not only in optical devices but are
expected to be promising candidates for intrinsic organic
conductors, non linear optical devices, solar cells and IR emitters
and detectors.
[0009] However, few low bandgap polymer materials are known which
show good optical device characteristics when used in an optical
device. These characteristics include the quantum efficiency of the
copolymer when excited to luminesce, the solubility and
processability of the polymer and the lifetime of the polymer when
used in a device. For electroluminescence the quantum efficiency is
defined as photons out per electron injected into the structure.
Other relevant characteristics for consideration are stability of
the polymer during use and storage of the device.
[0010] Low bandgap materials are not well known partly because they
are difficult to make.
[0011] It may be noted that polymers made by electrochemical
oxidative coupling usually are not suitable for use as emitters in
an electroluminescent device. This is because they have poor device
characteristics such as having a large number of defects and being
substantially insoluble and not processable.
[0012] In Windle et al. J. Org. Chem., 1984, 49, 3382 and Kobayshi
et al., J. Chem. Phys., 1985, 82, 5717 the reported discovery of
polybenzo[c] thiophene whose bandgap is about 1 eV lower than that
of polythiophene showed a possibility of tuning the bandgap by
structural modification. Recently, efforts have been devoted
theoretically and experimentally in order to explore the
correlation between the structures and bandgaps of polymers and to
further reduce bandgaps.
[0013] Several approaches to achieving a narrow bandgap have been
suggested. One is the copolymerisation of aromatic and o-quinoid
units, indicating that the combination of monomer segments with
different electronic structures can lower the bandgap through the
relaxation of bond-length alternation. This is discussed in Kurti
et al, J. Am. Chem. Soc. 1991, 113,9865.
[0014] Another approach is the alternation of strong
electron-donating and electron-accepting moieties as disclosed in
Havinger et al, Polym. Bull., 1992, 29, 119. This suggests that the
mixing of monomer segments with higher HOMO and lower LUMO is
effective to reduce the bandgap due to the intra chain charge
transfer. The affect of steric interaction between adjacent units
relating to coplanarity having regard to maximising the effective
conjugation length along the polymer backbone is addressed in Nayak
et al, Macro molecules, 1990, 23, 2237.
[0015] Narrow bandgap systems symbolised as A-Q-A .sub.n, where A
is a kind of aromatic-donor unit and Q is a kind of
o-quinoid-acceptor unit are disclosed in "Design of Narrow-bandgap
polymers", Chem. Mater., 1996, 8, pages 570-578. The bandgaps
determined from the polymers on ITO-coated glass electrodes vary
from 0.5 to 1.4 eV. The authors conclude that these values are
small compared with usual conjugated polymers, confirming that the
polymers are narrow-band gap systems. Furthermore, the authors
conclude that the results show that the bandgap is widely tuneable
by the polymer structure.
[0016] Despite work in the field of narrow bandgap polymers, there
is still a need for electroluminescent polymers with a chemically
tunable red light emission. In particular, there is a need for such
polymers which have, additionally, excellent device characteristics
as discussed above. For the purposes of the present invention, the
phrase red light means wavelengths in the range of 595 to 800 nm,
preferably 595 to 700 nm, preferably 610 to 650 nm, especially
around 630 nm and especially wavelengths having a peak around 650
to 660 nm.
[0017] Accordingly, it is an aim of the present invention to
overcome these deficiencies of the prior art and to provide such a
polymer.
[0018] It is a further aim of the present invention to provide uses
of the polymer.
[0019] In a first aspect, the present invention provides a
luminescent polymer comprising a triarylene repeat unit which
comprises a triarylene of general formula I which is substituted or
unsubstituted and an arylene repeat unit Ar that is different from
the triarylene repeat unit: 1
[0020] wherein X, Y and Z are each independently a group VI element
or an alkyl-or aryl-substituted group V or group IV element.
[0021] The applicants have unexpectedly found that the present
polymer acts as a low bandgap emitter. Furthermore, the present
applicants have found that the present polymer gives good "red"
emission as defined by the CIE coordinates X=0.66 and Y=0.33 or
good emission in the IR range, specifically near to far IR with
radiation having a wavelength of 700 nm or greater and has
properties which give good device characteristics. These properties
include solubility, processability, and good efficiency and
lifetime in a device.
[0022] In one embodiment the polymer comprising a triarylene repeat
unit which is an unsubstituted triarylene of formula: 2
[0023] is excluded from the first aspect of the present
invention.
[0024] In a further preferred embodiment, the present polymer
comprises repeat units of the general formula II:
triarylene repeat unit-Ar (II)
[0025] It is particularly advantageous for the molar ratio of
triarylene repeat unit: Ar to be up to approximately 1:1. However,
it is envisaged that the percent by weight triarylene could be in
the range 0.1-50%, preferably in the range 5-10%.
[0026] More preferably, the present polymer comprises repeat units
of the general formula III: 3
[0027] Preferably, the triarylene repeat unit comprises the general
formula IV: 4
[0028] wherein at least one of R.sub.1 to R.sub.6 comprises an
alkyl, aryl, heteroaryl, alkylaryl, arylalkyl, CN or halide
substituent. Preferably, the aryl, heteroaryl, alkylaryl or
arylalkyl is phenyl, heterophenyl, alkylphenyl or phenylalkyl.
[0029] Most preferably all of R.sub.1 to R.sub.6 are H.
[0030] The position and nature of substituent R groups may be
chosen so as to enhance solubility, efficiency and/or effect the
colour of emission by steric or electronic effects.
[0031] For the purposes of using the present polymer in an optical
device, it has been found by the applicants that substitution of
the colour of emission and also controlling (in particular,
narrowing) the width of emission.
[0032] In one preferred embodiment, R.sub.3 and/or R.sub.4 are
methyl.
[0033] In another preferred embodiment,
R.sub.1,R.sub.2,R.sub.3,R.sub.4,R.- sub.5 and R.sub.6 are all
H.
[0034] In another preferred embodiment, R.sub.1 and/or R.sub.6
comprise an alkyl, aryl, CN or halide while R.sub.2,R.sub.3,R.sub.4
and R.sub.5 are all H. More preferably, R.sub.1 and R.sub.6 each
comprise hexyl and R.sub.2,R.sub.3,R.sub.4 and R.sub.5 are all H.
This is because the applicants have found that substitution at
positions R.sub.2, R.sub.3, R.sub.4 or R.sub.5 leads to a twisting
of the triarylene unit. In turn, this reduces .pi.-conjugation and,
therefore, increases the bandgap. This would seem to be due to
steric hindrance. Electronic effects also may play a role in this
effect.
[0035] Several other polymers of particular interest in accordance
with the present invention are those where R.sub.1 to R.sub.6 are
all H, or where R.sub.1, R.sub.2, and R.sub.5 are all H while
R.sub.3 and R.sub.4 are methyl or where R.sub.1, R.sub.2, R.sub.3
and R.sub.6 are all H and R.sub.4 is methyl.
[0036] Preferably X, Y and Z are each independently O, S, C, Si or
N, more preferably, O or S. Still more preferably X, Y and Z all
are S. Again, it has been found that these groups result in
coplanar conformations of the polymer which maximises
.pi.-conjugation.
[0037] A further preferred embodiment may be where X and Z are O
and Y is S.
[0038] The applicants have found that arylene repeat units Ar which
are useful in the present polymer may advantageously comprise a
2,7-linked 9,9 dialkyl fluorene, a 2,7-linked 9,9 diaryl fluorene,
a p-linked dialkyl phenylene, a p-linked dialkoxy phenylene, a
phenylene vinylene, a 2,5-linked benzothiadiazole, a 2,5-linked
alkyl benzothiadiazole, a 2,5-linked dialkyl benzothiadiazole, a
2,5-linked substituted or unsubstituted thiophene, a triarylamine
or a bis triarylamine. Ar may be other substituted or unsubstituted
aromatic systems such as polycyclic aromatics, fused aromatics or
heterocycles.
[0039] In a further embodiment of the present invention, the
polymer further comprises a further repeat unit of general formula
V: 5
[0040] which repeat unit is substituted or unsubstituted, wherein Q
is O, S, CR.sub.2, SiR.sub.2 or NR, more preferably O or S, still
more preferably S.
[0041] The degree of polymerisation of the present polymer must be
sufficient to achieve bandgap convergence. Bandgap convergence
means the band gap obtained where any further increase in effective
conjugation does not affect the band gap. For the present purposes,
the degree of polymerisation is preferably at least 4.
[0042] The variables discussed above may be modified to tune
spectral, transport and physical (for example solution) properties
of the polymer.
[0043] As mentioned above, the present applicants have unexpectedly
found that the variables may be selected in order to obtain a
polymeric red emitter with excellent device properties. In essence,
each variable in the present polymer should be chosen so that the
polymer is capable of emitting light at a wavelength in the range
600 to 690 nm
[0044] Preferably, the variables are chosen also so as to make the
polymer soluble. This has the advantage of allowing the polymer to
be processed in solution.
[0045] The present polymer may be prepared by a number of
methods.
[0046] A preferred method of preparation is described in U.S. Pat.
No. 5,777,070. The process involves contacting (i) monomers having
two reactive groups selected from boronic acid, C.sub.1-C.sub.6
boronic acid ester, C.sub.1-C.sub.6 borane and combinations thereof
with aromatic dihalide functional monomers or (ii) monomers having
one reactive boronic acid, boronic acid ester or borane group and 1
reactive halide functional group with each other. Various aromatic
monomers are proposed including those containing triarylamines. The
polymerisation reaction product of this process has conjugated
unsaturated internal groups.
[0047] Another preferred method of preparation is described in
International patent publication No. Wo 00/53656. This describes
the process for preparing a conjugated polymer, which comprises
polymerising in a reaction mixture (a) an aromatic monomer having
at least two reactive boron derivative groups selected from a
boronic acid group, a boronic ester group and a borane group, and
an aromatic monomer having at least two reactive halide functional
groups; or (b) an aromatic monomer having one reactive halide
functional group and one reactive boron derivative group selected
from a boronic acid group, a boronic ester group and a borane
group, wherein the reaction mixture comprises a catalytic amount of
a catalyst suitable for catalysing the polymerisation of the
aromatic monomers, and an organic base in an amount sufficient to
convert the reactive boron derivative functional groups into
-BX.sub.3 anionic groups, wherein X is independently selected from
the group consisting of F and OH.
[0048] Polymers according to the present invention which have been
produced by this method are particularly advantageous. This is
because reaction times are short and residual catalyst e.g.
palladium levels are low.
[0049] The present invention further provides a composition
comprising a mixture comprising a luminescent polymer according to
this invention.
[0050] Preferably, the composition comprises a luminescent polymer
comprising a triarylene repeat unit which is an unsubstituted
triarylene of formula: 6
[0051] The composition may be in any suitable form, for example
laid down as a sheet or layer.
[0052] The present polymer may be used in an optical device such as
an optical device comprising an electroluminescent device. Such
devices may comprise a substrate and the present polymer supported
on the substrate.
[0053] Usually, such electroluminescent devices would comprise a
first charge carrier injecting layer for injecting positive charge
carriers, a second charge carrier injecting layer for injecting
negative charge carriers and a light-emissive layer located between
the charge carrier injecting layers for accepting and combining
positive and negative charge carriers to generate light.
Optionally, the electroluminescent device may comprise a material
for transporting negative charge carriers. This may either be
located between the second charge carrier injecting layer and the
light emissive-layer or may be located in the light-emissive layer.
Where it is located in the light-emissive layer, it may be blended
in a mixture with the light-emissive material. Also optionally, the
electroluminescent device may comprise a material for transporting
positive charge carriers. This either may be located between the
first charge carrier injecting layer and the light-emissive layer
or may be located in the light-emissive layer. Where it is located
in the light-emissive layer, it may be blended in a mixture with
the light-emissive material and optionally a material for
transporting negative charge carriers.
[0054] One example of a blend or mixture which is particularly
useful for use in the light-emissive layer of an electroluminescent
device according to this invention consists of the three polymers
shown below blended in a ratio of 99.6:0.2:0.2. The light-emissive
layer may consist only of this blend or may include further
polymers. This blend is capable of emitting white light when
excited to luminesce.
[0055] The blend: 7
[0056] where n.gtoreq.4, 0.05 .ltoreq.x+z.ltoreq.0.5 and
0.5.ltoreq.y and x+y+z.times.1. 8
[0057] where x+y=1, 0.5.ltoreq.x and y.ltoreq.0.5 and n.gtoreq.2.
9
[0058] where w+x+y=1, w.gtoreq.0.5, 0.ltoreq.x+y.ltoreq.0.5 and
n.gtoreq.2.
[0059] In a particularly preferred example of this blend, in
polymer 1, x=0.25, y=0.5 and z=0.25. In polymer 2, x:y is
96.37:3.63 (in mole %). In polymer 3, w:x:y is 80:10:10 (in mole %)
or 85:10:5 (in mole %).
[0060] Where the polymer according to the present invention is used
as a light-emissive material in the light-emissive layer of an
electroluminescent device, advantageously, it may be blended in a
mixture with a material for transporting negative charge carriers
and/or a material for transporting positive charge carriers. Where
the polymer according to the present invention is capable of
transporting positive and/or negative charge carriers when used in
an electroluminescent device, it advantageously may be blended in a
mixture with a light-emissive material in the light-emissive
layer.
[0061] Where the polymer according to the present invention is
blended in the light-emissive layer with one or more other
materials, particularly one or more other polymers, the polymer
according to the present invention preferably is present in the
blend at a level of 0.2-30%, more preferably 0.5-30%.
[0062] Where the polymer according to the present invention is
blended with at least two other polymers in a mixture in the
light-emissive layer, the polymer according to the present
invention preferably comprises a repeat unit as shown in Formula VI
or VII below: 10
[0063] or
EXAMPLES
Example 1
[0064] Preparation of the Trimer 11
[0065] A solution of freshly distilled (0.045 mbar/ 89.degree. C. )
2-(tributyl-stannyl)thiophene (78 mL, 245 mmol), dibromo
benzothiadiazole (30 g, 102 mmol), and
tetrakis(triphenyl-phosphine) palladium (0) (2.4 g, 2 mol%) in
toluene (500 mL) was refluxed. After 18 h, the reaction was allowed
to cool to room temp. and then reaction mixture was filtered
through celite. The filtrate was evaporated to dryness and then
washed with hexane to afford 26.74 g (95% yield, 100% purity HPLC).
12
[0066] Bromination:--To a solution of thiophene-dimethyl
benzothiadiazole-thiophene (11.18 g, 40 mmol) in DMF (100 mL)was
added dropwise N-bromosuccinimide (14.4 g) in DMF (100 mL). After
15 mins, the reaction was quenched by pouring onto a solution of
ice/ethanol. The product was filtered off and washed with water.
The product was recrystallised from THF to give 10.12 g (58%) of
the product trimer 1 as fine dark red crystals.
Example 2
[0067] Preparation of the Trimer 13
[0068] The procedure outlined for Example 1 was followed using
freshly distilled (0.045 mbar/89.degree. C.) 2-(tributyl-stannyl)
furan (7.2 mL, 22.8 mmol), dibromodimethyl benzothiadiazole (3.07
g, 9.53 mmol), and tetrakis (triphenylphosphine) palladium (0) (190
mg, 2 mol). After 18 h, the reaction was allowed to cool to room
temp. and then the solvent was removed under vacuum. Purification
by column chromatography (5:1 Hexane:EtOAc), followed by
recrystallisation from EtOAc afforded 1.52 g (54% yield, 100%
purity HPLC) of the desired compound as bright orange crystals;
.sup.1H NMR (CDCl.sub.3)7.67 (2H, dd, J 0.5, 1.8), 6.96 (2H, dd, J
0.7, 3.5), 6.67 (2H, dd, J 1.8, 4.5) , 2.57 (6H, s, 2x
CH.sub.3).
[0069] Bromination:--The procedure outlined for Example 1 was
followed using a solution of Furan-dimethyl benzothiadiazole-Furan
(900 mg, 3.0 mmol) in DMF (10 mL), N-bromosuccinimide (1.08 g) in
DMF (10 mL). After 10 mins, the reaction was quenched by pouring
onto a solution of ice/ethanol. Dichloromethane was then added and
the aqueous layer removed. The organic layer was evaporated to
dryness and the resulting residue recrystallised from
ethanol/toluene to give 1.17 g (85%) of the product "trimer 2" as
fine orange/brown crystals; .sup.1H NMR (CDCl.sub.3) 6.99 (2H, d, J
3.3), 6.65 (2H, d, J 3.4), 2.58 (GH, s, 2x CH.sub.3).
Example 3
[0070] Preparation of a Substituted Primer
[0071] Substituted versions of the trimers prepared in Examples 1
and 2 were prepared via the procedure described in Example 1 using
modified starting materials. Example procedures for the preparation
of modified starting materials are shown below. 14
[0072] The alkyl substituents are provided for increased
solubility.
Example 4
[0073] Preparation of the Polymer
[0074] A suspension of F8-diester (9.546 g, 18 mmol), dibromo-BT
(2.646 g, 9 mmol), "trimer 1" (4.109 g, 9 mmol) and tetrakis
(triphenyl phosphine) palladium (0) (60 mg) in toluene (180 mL) was
de-gased with nitrogen. After 1 h, tetraethyl ammonium hydroxide
(60 mL) was added to the reaction mixture and the suspension heated
to .about.115.degree. C. (external temp.). The reaction was
end-capped with bromobenzene (15 mL) after exactly 4 h 20 min.
Stirring was maintained at 115.degree. C. for 1 h then phenyl
boronic acid (2.5 g) was added and stirring continued for a further
1.5 h. Once the reaction mixture had cooled to r.t. the polymer was
precipitated into methanol (4L). The polymer was filtered off and
re-dissolved in toluene (500 mL). A solution of dithiocarbamic acid
(30 g) in H.sub.2O (220 mL) was added to the toluene solution. The
salt mixture was heat to 65.degree. C. for 18 h and then the
aqueous layer was removed. The organic phase was passed down an
alumina/silica column, eluting the polymer with toluene. The
toluene was condensed to 350 mL and then precipitated into methanol
(4L). The polymer was filtered off and dried thoroughly.
Example 5
[0075] An Optical Device
[0076] A suitable device structure is shown in FIG. 1. The anode 2
is a layer of transparent indium-tin oxide ("ITO") supported on a
glass or plastic substrate 1. The anode 2 layer has a thickness
between 1000-2000 .ANG., usually about 1500 .ANG.. The cathode 5 is
a Ca layer having an approximate thickness of 1500 .ANG.. Between
the electrodes is a light emissive layer 4 having a thickness up to
about 1000 .ANG.. The emissive layer 4 comprises between 0.5 to 30%
by weight of the present polymer with the remainder of the emissive
layer consisting of hole and/or electron transport material.
Advantageously, the device includes a hole transport material layer
3 of PEDOT having a thickness of about 1000 .ANG.. Layer 6 is an
encapsulant layer of a suitable thickness.
* * * * *