Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From fluorine-containing reactant
Patent
1996-02-16
1999-01-05
Truong, Duc
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From fluorine-containing reactant
528401, 526258, 526263, 359245, 313110, C08G 6522
Patent
active
058564349
DESCRIPTION:
BRIEF SUMMARY
There is a great industrial need for large-area solid state light sources for a series of applications, predominantly in the fields of display elements, VDU technology and lighting engineering. The demands made of these light sources can at present not be achieved completely satisfactorily by any of the existing technologies.
For about 30 years, organic electroluminescence materials and devices have been known in addition to inorganic ones (see, for example, U.S. Pat. No. 3,172,862). However, until recently such devices have been greatly restricted in their practicable usability.
WO 90/13148 and EP-A 0 443 861 describe electroluminescence devices containing a film of a conjugated polymer as light-emitting layer (semiconductor layer). In comparison with those known hitherto, such devices offer numerous advantages, such as the opportunity of producing large-area, flexible displays in a simple and inexpensive manner. In contrast to liquid crystal displays, electroluminescence displays are self-illuminating and therefore require no additional back-lighting source.
A typical device according to WO 90/13148 comprises a light-emitting layer in the form of a thin, dense polymer film (semiconductor layer) containing at least one conjugated polymer. A first contact layer is in contact with a first surface, a second contact layer with a further surface of the semiconductor layer. The polymer film of the semiconductor layer has a sufficiently low concentration of extrinsic charge carriers for charge carriers to be introduced into the semiconductor layer on application of an electric field between the two contact layers, with one contact layer becoming positive in comparison with the other, and the semiconductor layer emitting radiation. The polymers used in such devices are conjugated. A conjugated polymer is a polymer possessing a delocalized .pi.-electron system along the main chain. The delocalized .pi.-electron system gives the polymer semiconductor properties and enables it to transport positive and/or negative charge carriers with high mobility. An overview of conjugated polymers is given, for example, in R. H. Friend, J. Mol. Elec. 4 (1988) 37.
In WO 90/13148 and EP-A 0 443 861, the polymeric material used for the light-emitting layer is poly(p-phenylene-vinylene) and it is proposed that the phenyl group in such a material be replaced by a heterocyclic or a condensed carbocyclic ring system.
Although good results were obtained with these materials, the color purity, for example, is still unsatisfactory. Furthermore, it is hardly possible to generate a blue or white emission using the polymers which have hitherto become known.
Polymer Preprints 34 (1993) 532 describes structures in which individual, directly bonded chromophore segments are twisted with respect to one another to achieve a blue shift of the emission. However, according to the authors, it is not possible to produce light-emitting diodes from these materials.
It is an object of the present invention to provide conjugated polymer materials by means of which the above-described disadvantages can be at least partially remedied.
It has now been found that in particular the color purity of the emission of conjugated polymers can be significantly improved if their emission properties are predominantly determined by the emission properties of individual chromophores. This means that the chromophores of these polymers are decoupled in respect of the emission spectra.
The invention accordingly provides for the use in electrooptical switching and display devices of a polymer comprising conjugatively linked chromophore segments and spacer segments whose emission properties are determined by the emission properties of the individual chromophore segments.
Electroluminescence devices comprising such polymers have, inter alia, a high color purity. The polymers used according to the present invention enable, in particular, blue and white electroluminescence to also be achieved.
For the purposes of the invention, conjugation is when at least three sp.sup.2 -hybridiz
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Janssen et al., "Encapsulation of Inorganic Filler Particles by Emulsion Polymerization", pp. 532-533, Eindhoven Univ. of Tech., Dept. of Polymer Chem., PO Box 513, 5600 MB Eindhoven, The Netherlands.
von Seggern et al., "New Polymeric Materials for Blue and Green Light Emitting Diodes", pp. 532-533, Institute for Polymers and Organic Solids and Materials Dept., Univ. of California, Santa Barbara, CA 93106.
Leising Gunther
Mullen Klaus
Salbeck Josef
Schenk Hermann
Scherf Ullrich
Hoechst Aktiengesellschaft
Truong Duc
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