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.