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.