Reversible luminescence thermochromism of dibenzoyl (methanato)boron difluoride

Reversible luminescence thermochromism of dibenzoyl(methanato)boron difluoride was found. A substantial hypsochromic shift of the luminescence band maximum (60 nm) with a temperature decrease from 300 to 77 K was observed, and the luminescence color changed from green to blue. A considerable decrease (by 0.386 angstrom) in the unit cell parameters along the c axis was detected by X-ray diffractometry when the temperature of the crystal decreased from 293 to 123 K. Shortening of the distances between the planes of adjacent molecules (stacking factor) weakens the interaction between the dimers and enhances the monomeric and excimeric luminescence.