Room-Temperature Phosphorescence of Crystalline 1,4-Bis(aroyl)-2,5-dibromobenzenes

There is a growing interest in metal-free organic luminophores that exhibit phosphorescence at room temperature. We report herein that 1,4-bis(aroyl)-2,5-dibromobenzenes serve as a new class of such luminophores. The bis(aroyl)benzene derivatives were not emissive either in solution or in a doped polymer thin film. In contrast, crystals of bis(aroyl)benzenes showed photoluminescence under ambient conditions, which was subsequently confirmed as phosphorescence with a luminescence lifetime measurement. The emission color ranged from blue to green, depending on the nature of the aroyl groups, and the luminescent quantum yields were 0.05-0.18 at room temperature and 0.38-0.67 at 77 K. In each crystal, several intermolecular interactions such as C=OH, BrBr, C=OBr, FF, SH, and MeOH were observed, which contributed to the restriction of intramolecular motions, thereby diminishing the nonradiative decay process from the triplet excited states.