Dipole Effect of BN-Doped Tetrathienonaphthalene on Photo-Physical Properties and Lewis Acidity of the D-pi-A Derivatives

Dimesitylboryl-acceptor (A) and diarylamine-donor (D) substituents are introduced at alpha positions of BN-doped tetrathienonaphthalene in the same and opposite directions of the B-N bond, namely, B-BN-N and N-BN-B, in order to demonstrate how the substitution patterns influence the photo physical properties. The photophysical and electrochemical properties of these D-pi-A molecules have been investigated in detail, aided by UV-vis absorption and fluorescence spectroscopy as well as cyclic voltammetry. We find that both B-BN-N and NBN-B show the typical intramolecular charge transfer emission. NBN-B exhibits strong fluorescence with a narrower band gap and stronger Lewis acidity than that of B-BN-N. DFT calculations help give a reasonable explanation that subtle differences in the electronic structure of the host skeleton could also influence the substituents and feed back this effect to the entire molecule.