Statistical copolymers for blue-light-emitting diodes

Abstract

Fluorene-based statistical copolymers with m- and p-divinylbenzene were synthesized by the Heck reaction to fabricate blue-light-emitting diodes (LEDs). Photoluminescence (PL) spectra of the copolymers showed the maximum at 475 nm regardless of the concentration ratios between m- and p-divinylbenzene to reveal the complete energy transfer from the chromophore with the meta unit to the fluorophore of the para unit while 100% of the meta unit exhibited the emission maximum at 430 mo. The highest PL intensity was obtained with the ratio of 7/3 between the meta and pars units, However, the time-resolved picosecond fluorescence study on the polymer solution revealed that the intramolecular energy transfer alone in the copolymers was incomplete to suppress the emission at 430 nm. The electroluminescence (EL) center of the copolymers was the same as that of the PL to show the maximum at 475 nm. The highest-quantum efficiency of a single-layered LED fabricated with the light emissive copolymer with 30% of the para unit was observed to be 0.04%, which would be improved by optimization of the device characteristics.