Bisindolylmaleimides as red electroluminescence materials

Derivatives of bisindolylmaleimide were found to form amorphous solid films which exhibit red luminescence, and can be fabricated into light-emitting diodes. The property of forming glasses can be ascribed to the nonplanar geometry of these molecules. Single-crystal X-ray diffraction analyses revealed the presence of pseudo E and Z conformational isomers which are responsible for the phenomena of polymorphism detected by differential scanning calorimetry. All compounds exhibit distinct glass transition temperatures, and several show dual melting temperatures. Two kinds of devices were fabricated in which a layer of pure dye was sandwiched between opposite charge transporting layers. The emission spectra of devices utilizing tris(8-hydoxyquinolinato)aluminum (Alq) contained a green component from Alq. Pure red emissions can be achieved by replacing Alq with 2,2',2"-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole) (TPBI). Typical devices can be turned on at about 3 V with maximal intensity of similar to2000 cd/m(2).