Synthesis and properties of conjugated copolycondensates consisting of carbazole-2,7-diyl and fluorene-2,7-diyl

Carbazole and fluorene-based random and alternating copolycondensates were synthesized to develop high-performance blue light-emitting polymers by improving electron injection ability of poly(N-aryl-2,7-carbazole)s that showed intense blue electroluminescence (EL) with good hole-injection and -transport ability. These copolycondensates absorbed light energy at about lambda max = 390 nm in CHCl3 and 400 nm in film state, and fluoresced at about lambda max = 417 nm in CHCl3 and 430 nm in the thin film state. Energy gaps between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of them were about 2.9 eV, and the energy levels of LUMO situated lower than that of corresponding polycarbazole. Polymer light-emitting diode devices having configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)/polymer/CsF/Al using the copolycondensates, poly(N-arylcarbazole-2,7-diyl), and poly(9,9-dialkylfluorene-2,7-diyl), emitted bluish EL at operating voltages lower than 7 V. The device embedded the random copolycondensate showed notably higher performance with maximum luminance of 31,200 cd m-2 at 11.0 V, and the current efficiencies observed under operating voltages lower than 7 V were higher than those of the other devices. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012