Benzotristhiazole based chromophores for nonlinear optics

Methylation of unsymmetrical trimethylbenzotristhiazole with various reagents has been studied in details. The structure of obtained 2,3,5,8-tetramethylbisthiazolo[4,5-e;5,4-g]-1,3-benzothiazolium iodide has been proved by X-ray analysis in accord with the quantum-chemical calculations at DFT-B3LYP level. The electron-withdrawing tetramethylbenzotristhiazolium building block was submitted to Knoevenagel reaction with aromatic aldehydes containing an electron-releasing group. This led to a series of condensation products with push–pull structure. Relations between structure, linear (UV–Vis and fluorescence spectra) and nonlinear optical properties (calculated frontier orbital energy gap, BLA index, hyperpolarizabilities β and γ) have been investigated.

► Various methylations of unsymmetrical trimethylbenzotristhiazole were studied.
► The structure of the obtained monomethylated salt was proved by X-ray analysis.
► The X-ray analysis was in accord with the quantum-chemical calculations (DFT-B3LYP).
► A series of condensation products with push–pull structure was prepared.
► Relations between structure, linear and nonlinear optical properties were examined.