Optical Properties of Boron-Incorporated Analogues of Tetrathienoanthracene

Boron-introduced aromatic systems have caught the interest of materials chemists because of their unique photophysical properties and tunable Lewis acidity. In this work, we have prepared boron-incorporated analogues of tetrathienoanthracene (TTA) containing aromatic borepin rings. Despite the low aromaticity of the borepin rings, the bis-borepins showed high chemical stability and no decomposition in air. Interestingly, the bis-borepins exhibited bluish fluorescence at room temperature and bright greenish phosphorescence at a low temperature. The specific electronic structure of the boron-incorporated analogues of TTA was revealed by comparing the photophysical properties of the bis-borepins with those of TTA and the parent mono-borepin. The electronic structure was further investigated by DFT/TD-DFT calculations. Titration experiments using cyanide as the anion revealed the high Lewis acidity and the turn-off fluorescence response of the bis-borepins to the addition of cyanide.