Polymorphic β-diketone boron-difluoride crystals with distinct room temperature phosphorescence aroused by tiny differences in intermolecular interactions

Pure organic materials with robust room temperature phosphorescence (RTP) have been under wide investigation during the past years. In this work, we report two crystals of a β-diketone boron-difluoride bearing trimethyl-phenyl rings, which exhibit similar configuration and molecular stacking modes, but distinct luminescent properties. The bulky yellowish green-emissive crystal emits a yellow phosphorescence with a lifetime of 25.3 ms at room temperature, while the small-size crystal is blue-emissive with a phosphorescence lifetime of 92.4 μs. The distinct luminescent character of the two crystals is ascribed to the tiny differences in intermolecular interactions. Upon grinding, intense blue fluorescence with weak phosphorescence was observed, presenting a stimuli-responsive RTP property.