White light emission from a single component system: remarkable concentration effects on the fluorescence of 1,3-diaroylmethanatoboron difluoride

Abstract

Concentration effects on the fluorescence (FL) emission of 1,3-dibenzoylmethanatoboron difluoride (1aBF2) and its diisopropyl derivative (1bBF2) in KBr and CH2Cl2 were investigated. Powder samples of 1aBF2 and 1bBF2 in KBr exhibit yellow and white FL emissions, respectively, whose intensities and wavelengths are not significantly affected by concentration. In contrast, remarkable concentration effects on FL properties of these compounds in CH2Cl2 solutions were observed. Increases in the concentrations of 1aBF2 and 1bBF2 from 1×10−7 to ca. 2×10−1 M lead to dramatic changes in the FL colors from blue (398 and 411nm, respectively) to yellow (548 and 558nm) via white. Careful analysis of the FL spectra, involving lifetime determinations and wave deconvolutions, reveals that emissions from 1BF2 involve two FL domains, corresponding to an excited monomer and an excimer, and that concentration increases promote a continuous change from the former to the latter major FL domain. Thus, white FL of 1aBF2 and 1bBF2 is achieved by modulation of the dual FL of the excited monomer (blue) and excimer (yellow). These findings indicate that 1,3-diaroylmethanatoboron difluoride (1BF2) represents a new white emitting material that has advantageous features which arise from the fact that it is an easily prepared, low molecular weight, single component system not containing a heavy metal atom.