Syntheses and light-emitting properties of poly(9,9-di-n-octylfluorenyl-2,7-vinylene) and PPV copolymers

A new class of light-emitting poly(p-phenylenevinylene) (PPV) derivative, poly(9,9-di-n-octylfluorenyl-2,7-vinylene) (PFV), and its PPV copolymers, poly[(9,9-di-n-octylfluorenyl-2,7-vinylene)-co-(1,4-phenylenevinylene)]s [ poly(FV-co-PV)s] were synthesized through Gilch polymerization, and their light-emitting properties were investigated. The copolymers showed almost the same optical properties as the PFV homopolymer, regardless of copolymer composition. The PFV and copolymers all showed their peak absorption and band edge at around 419 and 490 nm, respectively. The PFV and poly(FV-co-PV) s all showed PL emission maxima at approximately 465 nm. Light-emitting devices were fabricated with the configuration ITO (indium-tin oxide)/PEDOT/polymer/Al. Interestingly, the EL spectra of these devices were similar to the PL spectra of the corresponding polymer film. However, the EL devices constructed from the poly(FV-co-PV) s showed 10 times higher efficiency than the devices constructed from the PFV homopolymer. This higher efficiency is possibly a result of better charge carrier balance in the copolymer systems due to the lower HOMO level (similar to5.5 eV) of the poly(FV-co-PV) s in comparison to that of PFV (similar to5.7 eV).