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 nm. The highest PL intensity was obtained with the ratio of 7/3 between the meta and para 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.

Excitation migration dynamics and the energy-transfer process in a donor−acceptor pair system on photoexcitation have been investigated by using static and time-resolved photoluminescence (PL) measurements. The PL spectrum of poly(N-vinylcarbazole) (PVK) was fully superposed on the electronic absorption spectrum of poly(9,9‘-di-n-hexyl-2,7-fluorenylvinylene) (PDHFV) to fulfill a requirement for an efficient Förster-type energy transfer. In the PL spectrum of a blended PVK film with 0.5 wt % PDHFV on photoexcitation at 340 nm, the PL emission of PDHFV, which exhibits little absorbance at the excitation wavelength, prevailed over the PL emission of PVK. The PL spectrum of a bilayered structure with a PVK layer thickness of 4 μm and a PDHFV layer thickness of 80 nm, which was prepared by spin-casting PDHFV solution in trichloroethylene on a PVK film, also showed the PL emission of PDHFV on photoexcitation of the PVK layer at 340 nm without a trace of the PL emission of PVK. Excitation energy migration through a PVK bulk was observed up to a PVK thickness of 23 μm. A time-correlated single-photon counting (TCSPC) study deduced an energy migration velocity of 3.5 × 106 cm/s and a dwell time between each hopping of 85 fs, respectively, in the PVK bulk of the bilayered structures with a PDHFV layer thickness of 10 or 80 nm.