Diarylmethylene-bridged triphenylamine derivatives encapsulated with fluorene: very high Tg host materials for efficient blue and green phosphorescent OLEDs

Abstract

Two bridged triphenylamine/fluorene hybrids, BTPAF1 and BTPAF2, were designed and synthesized through Friedel–Crafts reaction. Their thermal, electrochemical, electronic absorption and photoluminescent properties were fully investigated. Very high glass transition temperatures (Tg) were observed at 204 °C for BTPAF1 and 211 °C for BTPAF2, owing to the introduction of rigid fluorene and bridged triphenylamine unit. The encapsulation of a fluorene unit at the para positions of bridged triphenylamine greatly enhances their electrochemical stability. The linkage by the quaternary carbon atom of the fluorene moiety (C-9) effectively prevents the extension of π-conjugation of the bridged triphenylamine core, and consequently means that the compounds have a high triplet energy of 2.86 eV. Phosphorescent organic light-emitting devices (PHOLEDs) fabricated by using the two compounds as the hosts and the blue emitter bis[2-(4′,6′-difluorophenyl)pyridinato-N,C2′]iridium(III) picolate (FIrpic) as the guest exhibit good EL performances with a maximum current efficiency of 20 cd A−1, a maximum power efficiency of 14 lm W−1, and a maximum external quantum efficiency of 9.4%. Green electrophosphorescent devices by using green-emitter iridium(III) fac-tris(2-phenylpyridine) [Ir(ppy)3] as guest and the two new compounds as the hosts display excellent EL performances with a maximum current efficiency of 75 cd A−1, a maximum power efficiency of 60 lm W−1, and a maximum external quantum efficiency of 19.5%. The device figures of merit, together with the excellent morphological and electrochemical stabilities, make the new compounds ideal host materials for PHOLEDs, especially for high-temperature applications of devices.