Conjugated copolymers for use in luminescent devices

Details Conjugated copolymers for use in luminescent devices Conjugated copolymers for use in luminescent devices

1999-03-19

2002-07-23

Acquah, Samuel A. (Department: 1711)

Stock material or miscellaneous articles

Composite

Of inorganic material

C528S373000, C528S374000, C528S380000, C528S391000, C528S481000, C528S50200C, C528S503000, C524S401000, C428S457000, C428S463000, C428S500000, C428S521000, C428S524000, C252S301160, C252S500000, C252S301350, C385S141000, C385S143000, C385S145000

Reexamination Certificate

active

06423428

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to conjugated polymers for use in luminescent devices, especially electroluminescent devices, and their synthesis.
BACKGROUND TO THE INVENTION
Conjugated polymers have been used as organic electroluminescent (EL) materials in suitable device structures, as demonstrated in our earlier patent herein incorporated by reference as U.S. Pat. No. 5,399,502. Poly(p-phenylene vinylene) is one such polymer and may be prepared via the Wessling precursor method as described in, for example “Precursor Route to Poly(p-phenylene vinylene): Polymer Characterisation and Control of Electronic Properties” D. D. C. Bradley, J. Phys. D. 20, 1389 (1987). For example, a tetrahydrothiophene-based precursor with a halide counter-ion is typically used as shown in FIG.
1
. It has been proposed that the polymerisation of the p-xylenebis(sulphonium halide) monomer occurs via a quinoid intermediate as described in “The Polymerisation of Xylylene Bisdialkyl Sulfonium Salts” R. A. Wessling, J. Pol. Sci. Pol. Symp. 72, 55-66, (1985). The conjugated polymer formed is insoluble and intractable and therefore the solution processable precursor is required. Device fabrication is carried out using the precursor material and the conjugated polymer is prepared in situ via a thermal conversion step. Typically, the precursor polymer is coated, by spin-coating or blade coating or other coating techniques, onto a transparent conductive oxide layer, for example Indium Tin Oxide (ITO). The ITO is itself coated onto a suitable substrate which may be, for example, glass or plastic. The precursor polymer film is then converted on the ITO by suitable heat treatment. Following this, appropriate metal electrodes are deposited. A multi-layer structure is therefore obtained which consists of an anode, the conjugated polymer, and the cathode. Injection of positive and negative charge carriers at the anode and cathode respectively leads to light emission. Other layers may be included into the device to facilitate charge injection/accumulation or to afford protection during the conversion process. This is shown in FIG.
2
.
The advantages of using precursor conjugated polymers as emissive layers in EL devices include:
a) ease of fabrication,
b) amenable to multilayer structures,
c) intractability of converted polymer film, and
d) intrinsic luminescence properties.
However, there is some evidence that the quantum yield for radiative decay of the excited states is lowered through their migration to non-radiative decay centres hence photoluminescence and therefore electroluminescence efficiencies are significantly reduced. Our previous patent , herein incorporated by reference as U.S. Pat. No. 5,401,827 has dealt with this issue by describing a semiconductive conjugated copolymer comprising at least two chemically different repeat units with different semiconductor band gaps (for example conjugated and non-conjugated segments). The optical properties of the copolymer are therefore determined by the relative proportions of the different repeat units. Copolymers were prepared in this work either by copolymerisation of more than one bis(sulphonium) salt, control of the degree of conversion of the precursor polymer, or by the substitution of the THT unit to provide groups that would survive the conversion process. The latter approach is shown in FIG.
3
and will henceforth be referred to as the Substitution Approach.
We now have evidence that conversion of precursor homopolymer or copolymer systems on certain conductive oxide substrates such as ITO, can lead to undesirable interactions that give rise to either quenching of luminescence or to modification of the expected copolymer composition. Furthermore, we have observed that the presence of certain functional groups in the copolymer can be detrimental to device performance, and in particular to device lifetime.
SUMMARY OF THE INVENTION
The present invention seeks to provide conjugated arylene vinylene copolymer systems prepared via the precursor approach as emissive layers in EL devices which overcome these difficulties and retain the benefit of enhanced photoluminescence and electroluminescence efficiency.
The present invention provides a process for the preparation of a conjugated poly(arylene vinylene) copolymer for use in a luminescent device, which comprises:
(1) providing a precursor polymer comprising units of general formula
in which Ar is substituted or unsubstituted arylene, L is a leaving group, R
1
and R
2
are each independently H, alkyl, alkoxy, aryl or an electron-withdrawing group, and n is an integer;
(2) reacting the precursor polymer with a reactant comprising a carboxylate, an aldehyde, a ketone, a sulphonate, a thioate, a disulphide, a xanthate, an amine, a pyridine, a hydrazide, a phenoxide, an alcohol with a boiling point above 100° C., or a derivative thereof, under substitution conditions whereby a proportion of the leaving groups are substituted to form a substituted precursor copolymer comprising units of general formula &Parenopenst;ArCHR
1
—CR
2
L&Parenclosest;
m
&Parenopenst;ArCHR
1
—CR
2
X&Parenclosest;
l
, in which Ar, R
1
, R
2
and L are as defined above, X is a substituent group from the reactant, l and m are independently integers; and
(3) converting the substituted precursor copolymer to a conjugated poly(arylene vinylene) copolymer by elimination of the leaving groups from the substituted precursor copolymer.
Throughout this specification, the term arylene is intended to include in its scope all types of arylenes including heteroarylenes as well as arylenes incorporating more than one ring structure, including fused ring structures. Ar may be paraphenylene, 1,4 naphthylene, 1,4 anthracene, 2,6 fluorene and is preferably paraphenylene.
R
1
and R
2
may be independently selected from C
1
-C
10
alkyl, C
1
-C
10
alkoxy, aryl such as substituted or unsubstituted phenyl, heterocyclic or polycyclic aryl, —CN or —CF
3
. Preferably both R
1
and R
2
are H.
Where the reactant comprises a carboxylate, a carboxylate salt is preferred. In this way, the precursor polymer may be made conventionally such as by base-catalysed polymerisation from suitable monomers such as paraxylylene bis(tetrahydrothiophenium bromide). The carboxylate salt is then added to the precursor polymer. Other suitable monomers are described in U.S. Pat. No. 5,401,827.
Advantageously, the precursor polymer may be provided by base-catalysed polymerisation from suitable monomers in a molar excess of base. In this way, the carboxylate salt is formed by neutralisation of the base with its corresponding carboxylic acid. One advantage of this method is that it can be carried out in a single reaction zone such as a suitable container, in which the precursor polymer is formed in the excess base and, after polymerisation is complete, neutralisation takes place so as to form the substituted precursor copolymer prior to conversion into the conjugated poly(arylene vinylene) copolymer.
The carboxylate may be aliphatic such as formate or acetate and may be formed by the corresponding aliphatic carboxylic acids, formic acid or acetic acid. Substituted or unsubstituted aromatic carboxylates may be used such as those formed from 2,6 dimethylbenzoic acid, as well as derivatives thereof.
Materials of the following general formulae may be used:
R′—CO
2
H or Ar′—CO
2
H,
where R′=(cyclo)alkyl chain, Ar′=substituted or unsubstituted aromatic or polycyclic system.
In a further embodiment of this invention the substitution approach may be facilitated by the interaction of precursor polymer with a basic solution of a ketone or aldehyde (ie carbonyl) based system. Typical carbonyl based systems have the general structure shown and would include benzaldehyde, anthraldehyde, and benzophenone:
R
3
R
4
C=O or R
3
HC=O,
in which R
3
and R
4
are each independently R′ or Ar′ as defined above.
In a further embodiment of this invention oxygen, sulphur and nitrogen nucleophiles may be used to form PPV precursor

Affiliated with

Also associated with

Rating

Conjugated copolymers for use in luminescent devices does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Conjugated copolymers for use in luminescent devices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Conjugated copolymers for use in luminescent devices will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2846347