Novel blue-greenish electroluminescent poly(fluorenevinylene-alt- dibenzothiophenevinylene)s and their model compounds

Poly(9,9-dihexylfluorene-2,7-vinylene-alt-dibenzothiophene-2,8-vinylene) (PS) and poly(9,9-dihexylfluorene-2,7-vinylene-alt-dibenzothiophene-5,5-dioxide- 2,8-vinylene) (PSO) as well as corresponding model compounds were synthesized by Heck coupling. Both the polymers and model compounds were readily soluble in common organic solvents such as tetrahydrofuran, dichloromethane, chloroform, and toluene. The polymers showed a decomposition temperature at ∼430°C and a char yield of about 65% at 800°C in N₂. The glass-transition temperatures of the polymers were almost identical (75-77°C) and higher than those of the model compounds (26-45°C). All samples absorbed around 390 nm, and their optical band gaps were 2.69-2.85 eV. They behaved as blue-greenish light emitting materials in both solutions and thin films, with photoluminescence emission maxima at 450-483 nm and photoluminescence quantum yields of 0.52-0.72 in solution. Organic light-emitting diodes with an indium tin oxide/ poly(ethylene dioxythiophene):poly(styrene sulfonic acid)/polymer/Mg:Ag/Ag configuration with polymers PS and PSO as emitting layers showed green electroluminescence with maxima at 530 and 540 nm, respectively.