Structural and mechanistic studies of excitation- and temperature-tunable multicolor luminescence of triarylborane

The development of single-component organic systems with different phosphorescence behaviors remains a formidable challenge. Herein, an organic triarylborane has been synthesized, (3-bromo-2-(phenylethynyl)phenyl)dimesitylborane (1), which can be obtained as racemate (rac-1) and conglomerate (cong-1) crystals by solvent-induced recrystallization. Rac-1 contains two enantiomeric molecules, R-1 and S-1, while cong-1 is composed of isomorphic cong-R-1 and cong-S-1. Rac-1 and cong-1 crystals show different phosphorescence emissions at room temperature. Rac-1 exhibits color-tunable emission, while cong-1 has none. In addition, both exhibit color-tunable behavior at different temperatures, and the cong-1 crystal shows white-light emission with a Commission International de l'Eclairage (CIE) 1931 coordinate of (0.33, 0.31) at 280 K. In situ single crystal experiments and theoretical calculations reveal that the different luminescence behaviours due to photoexcitation or temperature originate from the change of molecular conformation. This method provides a new design strategy for color-tunable emission of organoborane molecules.