Spontaneous formation of a large area, aligned, ordered, π-conjugated film with polarized fluorescence and an amplified spontaneous emission based on a liquid crystalline bi-1,3,4-oxadiazole derivative

Abstract

A large area, aligned, ordered, π-conjugated film of a liquid crystalline bi-1,3,4-oxadiazole derivative (BOXD-5) (up to several square millimeters) with polarized fluorescence (I_max/I_min of 6.0, Φ_F = 72%) and a deep blue amplified spontaneous emission (ASE) (λ = 405 nm, threshold of about 2 kW cm⁻²) can be easily obtained upon cooling from its nematic phase with homeotropic texture in air at room temperature without the help of an alignment layer. The laser damaged aligned BOXD-5 film sandwiched between untreated glass slides can “self heal” through an easy heating–cooling thermal process. Neither the polarized fluorescence nor the ASE phenomenon were observed in the vacuum evaporated film. The directional π–π interactions between the 1,3,4-oxadiazole rings and phenyl rings, and its peculiar mesophase sequence cooperatively sustain a large area, aligned, ordered, π-conjugated film with polarized fluorescence and an ASE.