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.