High luminescent efficiency in light-emitting polymers due to effective exciton confinement

Highly efficient light-emitting polymers have become possible by molecular engineering. Photoluminescence (PL) quantum yield above 90% in the solid st ate is reported for the alternating block copolymer of distyrylbenzene. We conclude that the alternate arrangement of conjugated and nonconjugated seg ments with surrounding side groups for chromophores effectively confine the excitons for radiative emission. The effectiveness of the exciton confinem ent is confirmed through the temperature independence of the PL quantum yie ld. The time-resolved PL decay measurement supports this model through the independence of the PL yield on temperature and emission wavelength. The sy nthesized copolymers have been employed for the fabrication of electrolumin escent (EL) devices, demonstrating high external EL efficiency with low ope ration threshold. (C) 2000 American Institute of Physics. [S0003-6951(00)03 405-7].