Luminescence and reversible luminescence thermochromism of bulk and microcrystals of dibenzoylmethanatoboron difluoride

Essential differences in the luminescence properties of dibenzoylmethanatoboron difluoride (1) bulk and microcrystals were detected. Analysis of the spectral data showed that in every case the fluorescence spectrum of 1 consisted of three components: monomer fluorescence, excimer fluorescence, and fluorescence related with interdimer interaction. Evolution of luminescence spectra observed with decrease of the crystal size are bound with decrease of monomer fluorescence intensity and considerable growth of intensity of fluorescence related to interdimer interaction. The presence of reversible luminescence thermochromism was discovered for 1: lowering the temperature from 300 to 77 K resulted in essential hypsochromic shift of the luminescence band maximum (similar to 60 nm) connected with considerable decrease of the distances between the planes of the neighboring molecules (similar to 0.1 angstrom) that lead to the weakening of interdimer interaction and intensification of monomer luminescence.