Organic light-emitting diodes (OLEDs) composed of a novel fluorene derivative of 2,3-bis(9,9-dihexyl-9H-fluoren-

2-yl)-6,7-difluoroquinoxaline (F2Py) were fabricated, and exciplex emission was observed in the device. To depress the

exciplex in an OLED for pure colour light emission, 4, 4’-N,N’-dicarbazole-biphenyl (CBP) was inserted as a separator

at the donor/acceptor interface. It was found that the device without the CBP layer emitted a green light peaking

at 542 nm from the exciplex and a shoulder peak about 430 nm from F2Py. In contrast, the OLED with CBP layer

emitted only a blue light peak at about 432 nm from F2Py. Device efficiencies were calculated by a simulative mode

in an injection controlled type mechanism, and the results showed that exciplexes yield much lower quantum efficiency

than excitons. The device with CBP has a higher power efficiency as no exciplex was present.