Diarylmethylene-bridged 4,4′-(bis(9-carbazolyl))biphenyl: Morphological stable host material for highly efficient electrophosphorescence

A novel compound (BCBP) based on the modification of a well-known host material 4,4′-(bis(9-carbazolyl))biphenyl (CBP) through arylmethylene bridge linkage was synthesized, and fully characterized. Its thermal, electrochemical, electronic absorption and photoluminescent properties were studied. A high glass transition temperature (T_g) of 173 °C is observed for BCBP due to the introduction of the bridged structure, remarkably contrasting with a low T_g of 62 °C for CBP. Furthermore, the bridged structure enhances the conjugation and raises the HOMO energy, thus facilitating hole-injection and leading to a low turn-on voltage in an electroluminescent device. With the device structure of ITO/MoO ₃/NPB/Ir complex: BCBP/BCP/Alq₃/LiF/Al, maximum power efficiencies of 41.3 lm/W and 6.3 lm/W for green- and blue-emitting OLED were achieved, respectively.