Polyfluorene terpolymers containing phenothiazine and fluorenone: Effects of donor and acceptor moieties on energy and intrachain charge transfer processes in the photoluminescence and electroluminescence of multichromophore copolymers

Five new conjugated terpolymers containing 9,9-dihexylfluorene, 10-hexylphenothiazine (HPT) donor, and 9-fluorenone (FLO) acceptor were synthesized by Suzuki copolymerization and used to study the effects of competing energy and intramolecular charge transfer processes on the photoluminescence (PL) and electroluminescence (EL) of multichromophore copolymers. The HPT and FLO moieties were found to act as emissive exciton traps on the terpolymer chains, leading new blue-green (475-485 nm) and green (520-525 nm) emission bands in addition to the blue (415 nm) emission of the fluorene segments. Additional charge transfer excited states and associated nonradiative decay channels resulting in factors of 2-4 decrease in the solution PL quantum yields of the terpolymers emerged due to the HPT moieties. As the emissive materials in light-emitting diodes (LEDs), the terpolymers showed green to yellow EL with luminances of 1900-8970 cd/m(2) and efficiencies of 0.5-3.5 cd/A that varied with terpolymer composition. As a result of charge trapping within the HPT and FLO moieties, the EL spectra were very sensitive to the applied voltage, the terpolymer composition, and device architecture. These results highlight the complex excited-state dynamics encountered upon incorporation of electron-donating and -accepting moieties in polyfluorenes and have implications for the design of multichromophore EL copolymers for white LEDs.