Structure and Photophysics of N‐Tolanyl‐phenochalcogenazines and their Radical Cations

Abstract

AbstractThe study focuses on the structural and photophysical characteristics of neutral and oxidized forms of N‐tolanyl‐phenochalcogenazines PZX‐tolan with X=O, S, Se, and Te. X‐ray crystal structure analyses show a pseudo‐equatorial (pe) structure of the tolan substituent in the O, S, and Se dyads, while the Te dyad possesses a pseudo‐axial (pa) structure. DFT calculations suggest the pe structure for O and S, and the pa structure for Se and Te as stable forms. Steady‐state and femtosecond‐time resolved optical spectroscopy in toluene solution indicate that the O and S dyads emit from a CT state, whereas the Se and Te dyads emit from a tolan‐localized state. The T1 state is tolan‐localized in all cases, showing phosphorescence at 77 K. The heavy atom effect of chalcogens induces intersystem crossing from S1 to Tx, resulting in a decreasing S1 lifetime from 2.1 ns to 0.42 ps. The T1 states possess potential for singlet oxygen sensitization with a high quantum yield (ca. 40 %) for the O, S, and Se dyads. Radical cations exhibit spin density primarily localized at the heterocycle. EPR measurements and quasirelativistic DFT calculations reveal a very strong g‐tensor anisotropy, supporting the pe structure for the S and Se derivatives.