Third-order nonlinear optical properties of unsymmetrical tetrazole-based dyes and study the effect of electrostriction on reverse saturation absorption

This work was done to synthesize tetrazole dye and Z-scan measurement of the synthesized tetrazole compounds has been carried out and interesting results about the origin of positive nonlinear absorption coefficients of dye molecules were obtained. Investigation of linear optical properties of synthesized dyes was done with the help of visible UV absorption, and fluorescence emission spectrum. Also, the electronic characteristics and molecular geometry of the sensitizers were optimized using density functional theory (DFT), and the influence of dye structure on their nonlinear optical performances was studied. Four new dyes with D–π–A architecture were discussed, in which diphenylamine and carbazole units act as donors, methine groups act as conjugated bridge units, and tetrazole derivatives act as acceptor units. Diphenylamine, carbazole, methine, and tetrazole derivatives are, respectively, donor, conjugate, and bridge acceptor units in the structure of these dyes. Moreover, nonlinear absorption and refractive indexes of the synthesized tetrazole components were measured using the Z-scan technique equipped with a 50 mW CW Nd-Yag laser. The nonlinear absorption coefficient of tetrazole derivations was obtained and was positive, and it was demonstrated that the origin of the so-called reverse saturation absorption of dye molecules in low intensities is the electrostriction effect which is due to polarization of the molecules which has an inverse relation with the Homo–Lumo energy gap of the components.