Synthesis and properties of novel electroluminescent oligomers containing carbazolylene-vinylene-sulfonylene units for a light-emitting diode

As a new class of spin-coatable electroluminescent oligomers, oligo(N-ethylhexyl-3,6-carbazolylenevinylene-alt-4,4'-diphenyl-vinylene-sulfone) (P1 and oligo(N-ethylhexyl-3,6-carbazoledivinylene-p-phenylenevinylene) (P2) were synthesized through Wittig polycondensation of N-(2-ethylhexyl)-3,6-diformyl carbazole with the diphosphonium salts of bis(bromomethyl-p-phenyl)sulfone and alpha,alpha'-dibromo-p-xylene, respectively. These electroluminescent (EL) oligomers were highly soluble in common organic solvents, forming excellent-quality optical films by spin coating. Films obtained were very transparent, tough, and smooth with initial decomposition temperature of ca. 400 degreesC. Greenish-blue photoluminescence (PL) and electroluminescence (EL) was obtained for both oligomer films. It was found that the relative EL quantum efficiency of single-layer P1 device was five-fold higher than that of the P2 device, which was attributed to the lowered molecular energy levels of the former due to the presence of the sulfonylene group. (C) 2001 Elsevier Science B.V. All rights reserved.