Aromatic poly(1,3,4-heterodiazoles) for use in optical...

Details Aromatic poly(1,3,4-heterodiazoles) for use in optical... Aromatic poly(1,3,4-heterodiazoles) for use in optical...

2001-05-24

2002-11-05

Truong, Duc (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Nitrogen-containing reactant

C528S288000, C528S289000, C528S299000, C528S302000, C528S304000, C528S363000, C528S364000, C528S370000, C528S373000, C528S397000

Reexamination Certificate

active

06476184

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a filing under 35 U.S.C. §371 of PCT/EP99/06452, filed Sep. 2, 1999, which claims priority to German Application No. 198 40 195.7, filed Sep. 3, 1998.
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to main-chain polymers based on aromatic poly(1,3,4-heterodiazoles) which are suitable for use as the electroluminescent and/or electron-transport layer in optical devices, especially for light-emitting diodes (LEDs), and to a process for preparing them.
2. The Relevant Technology
The utilization of redox-active polymers and organic monomer compounds in optical devices is opening up the possibility of using simple processing techniques to realize large-area displays possessing low operating voltages and an emission over the entire spectral range, which it has not been possible to produce using the existing, conventional inorganic materials. Moreover, in contrast to the liquid-crystal displays, the electroluminescent displays are self-illuminating and therefore require no backlighting source.
Tang and van Slyke were the first to present LEDs based on organic materials (C. W. Tang, S. A. van Slyke;
Appl. Phys. Lett.
51 (1987) 913). As a result it was possible to increase the luminescence efficiency relative to the inorganic materials and to produce LEDs which emit blue light. The organic multiple or single layers form sandwich structures between a transparent indium-tin oxide (ITO) anode and a metal cathode with a output function, such as Mg, Al or Ca, for example. With the structure of multiple layer systems consisting of electron-transport layer, emitter layer and hole-transport layer it was possible to increase the luminescence efficiency and its stability (C. Adachi, T. Tsutsui, S. Saito;
App. Phys. Lett.
57 (1990) 531; Y. Hamada, C. Adachi, T. Tsutsui, S. Saito;
Jpn. J. Appl. Phys.
31 (1992) 1812). Where monomers are used, the layers are realized by means of specific and hence costly vapour deposition techniques. The use of polymers permits a simplified structure of the device.
Conjugated polymers having semiconductor properties with energy gaps of between 3.5 and 1.0 eV, such as the mentioned poly(p-phenylenevinylene) (PPV) or poly-(p-phenylene) (PP), are used as emitters and/or hole-transport layers in the device structure of LEDs. It is necessary to synthesize organic-soluble materials in order to apply these polymers appropriately by means of processes that are simple to manage, such as spin coating or dipping, for example. One synthesis route is the preparation of soluble prepolymers which are converted into the corresponding insoluble conjugated polymers by a subsequent pyrolysis step.
Intense research work into PPV has been carried out, inter alia, by Friend et al. (A. B. Holmes, D. D. Bradley, A. R. Brown, P. L. Burn, R. H. Friend;
Synthetic Metals
55-57 (1993) 4031, J. H. Burroughes, D. D. C. Bradley, R. H. Friend, EP 0423 283 B1) and by Hörhold et al. (M. Helbig, H. H. Hörhold;
Makromol. Chem.
194 (1993) 1607; H. H. Hörhold et al. DE 195 05 416 A1). Polymeric and oligomeric thiophenes have also been found to be particularly attractive. They permit the controlled adjustment of the wavelength of the light to be emitted, by variation of the substituents attached to the heterocycle (M. Granström, M. Berggren and O. Inganãs;
Science
267 (1995) 1479; E. G. J. Staring et al.;
Adv. Mater.
6 (1994) 934), although the quantum efficiency is unsatisfactory.
The structure of multilayer systems on a polymer basis makes it possible to increase considerably the efficiency of the emitting diodes. As additional layers which both improve the passage of the electrons through the layer and provide a barrier for holes, use has been made to date, inter alia, of side-chain polymers based on polymethacrylate with 1,3,4-oxadiazole groups in the side chain (X.-C. Li, F. Cacialli, M. Giles, J. Grüner, R. H. Friend, A. B. Holmes, St. C. Moratti, T. M. Yong,
Adv. Mater.
7, 1995, 898) and copolymers with 1,3,4-oxadiazole units in the main chain (E. Buchwald, M. Meier, S. Karg, P. Pösch, H.-W. Schmidt, P. Strohriegel, W. Rie&bgr;, M. Schwoerer,
Adv. Mater.
7, 1995, 839, Q. Pei, Y. Yang,
Adv. Mater.
7, 1995, 559).
Despite the enormous progress in the use of these materials in LEDs, the components still have limits with regard to service life, photostability, and stability to water and air.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide polymers which possess electroluminescence properties and/or electron-transport properties and/or improvement with regard to the target profile of properties of the component as a whole, so that it can be used in illumination or display devices.
The invention provides aromatic poly(1,3,4-heterodiazoles) comprising aromatic poly(1,3,4-heterodiazole) comprising from 100 to 1,000 repeating units selected from the group consisting of
in which R
1
, R
2
, R
3
and R
4
may be identical or different and are each an alkyl, alkoxy, phenyl, phenoxy or thiophenol group and X is S, O or N-phenyl.
One preferred class of the aromatic poly(1,3,4-heterodiazoles) of the invention has the general formula
in which R
1
and R
2
are as defined above and n is an integer from 100 to 1,000.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As discussed above, the present invention provides aromatic poly(1,3,4-heterodiazoles) comprising aromatic poly(1,3,4-heterodiazole) comprising from 100 to 1,000 repeating units selected from the group consisting of
in which R
1
, R
2
, R
3
and R
4
may be identical or different and are each an alkyl, alkoxy, phenyl, phenoxy or thiophenol group and X is S, O or N-phenyl.
One preferred class of the aromatic poly(1,2,4-heterodiazoles) of the invention has the general formula
in which R
1
and R
2
are as defined above and n is an integer from 1 to 1,000.
As already mentioned, the substituents R
1
to R
4
may be alkyl groups. These generally have 1 to 18 carbon atoms, preferably up to 16 carbon atoms. Similar comments apply to the abovementioned alkoxy group.
The alkyl and alkoxy groups may be linear or branched, and it is preferred to select the substituents R
1
and R
2
and, if appropriate, R
3
and R
4
such that one of these radicals is branched while the other radical or radicals is or are linear.
The substituents R
1
, R
2
, R
3
and R
4
may also be abovementioned alkyl and alkoxy groups in which one or more non-adjacent CH
2
groups have been replaced by —O—or —S—.
Furthermore, R
1
, R
2
, R
3
and R
4
may be a phenyl, phenoxy or thiophenol group.
The aromatic poly(1,3,4-heterodiazoles) of the invention are prepared by a process which is characterized in that equimolar amounts of an acid dichloride or two or more acid dichlorides, selected from the group consisting of
in which R
1
, R
2
, R
3
and R
4
are as defined in claim
1
, and of a dicarboxylic hydrazide or two or more dicarboxylic hydrazides, selected from the group consisting of
in which R
1
, R
2
, R
3
and R
4
are as defined in claim
1
, are subjected to a condensation polymerization, the condensation product is isolated, purified and then subjected to a ring-closure reaction in the presence of a water-withdrawing agent, and then the product is isolated and purified.
The water-withdrawing agent used is preferably phosphorus oxychloride.
Where sulphur or N-phenyl is to be introduced into the heterodiazole ring in place of oxygen, then aniline (to introduce N-phenyl) or phosphorus pentasulphide (to introduce sulphur) is added simultaneously during the ring-closure reaction. Solvents used are preferably benzene, toluene, xylene and 1,2-dichlorobenzene. The reaction temperature is preferably from 80 to 170° C. and the reaction time is from 2 to 20 hours. The polymers obtained are isolated by precipitation from a non-solvent and may be purified by extraction, with alcohols, for example, or by further dissolution and precipitation from a non-solvent.
As already mentioned, the corresponding polyhydrazides are prepared by condensat

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