Phase- and Halogen-Dependent Room-Temperature Phosphorescence Properties of Biphenylnitrile Derivatives

The photophysical properties of halogenated biphenylnitrile derivatives (X-BPhN, X = F, Cl, and Br) were systematically investigated, and bromobiphenylnitrile (Br-BPhN)-based solids exhibit phase-dependent room-temperature phosphorescence (RTP) characteristics. The perfect crystalline, lower-quality crystalline, and amorphous solids of Br-BPhN were prepared and exhibited different RTP properties. Two kinds of crystals obtained by slow vacuum gradient sublimation (crystal 1: high-quality crystal) and quick solvent evaporation (crystal 2: low-quality crystal) are attributed to an identical crystalline phase. The absolute phosphorescence quantum yields (ΦP) for crystal 1 and crystal 2 are 9.1 and 6.0%, respectively, while the amorphous sample Br-BPhN has an extremely low ΦP of 1.4%. Theoretical calculations and experimental results demonstrate that multiple intermolecular interactions including halogen bond-induced rigid supramolecular frameworks in the crystalline phase can enhance the RTP of Br-BPhN-based solids. This contribution presents a useful mode molecule to study the mechanism of organic RTP and may provide a feasible approach to develop pure organic phosphors with efficient RTP feature.