Add time:09/26/2019         Source:sciencedirect.com

Two series of related donor–acceptor conjugated heterocyclic azo dyes based on the thienylpyrrole system, functionalized with benzothiazol-2-yl (5–6) or benzothiazol-6-yl acceptor groups (7) through an NN bridge, have been synthesized by azo coupling using 1-alkyl(aryl)thienylpyrroles (1) and benzothiazolyl diazonium salts (2–4) as coupling components. Their optical (linear and first hyperpolarizability), electrochemical, and thermal properties have been examined. Optimized ground-state molecular geometries and estimates of the lowest energy single electron vertical excitation energies in dioxane solutions were obtained using density functional theory (DFT) at the B3LYP/6-31+G(d,p) level. Hyper-Rayleigh scattering (HRS) in dioxane solutions using a fundamental wavelength of 1064 nm was employed to evaluate their second-order nonlinear optical properties. Of these systems, the benzothiazol-2-yl-diazenes 5–6 exhibit the largest first hyperpolarizabilities (β=460–660×10−30 esu, T convention) compared to benzothiazol-6-yl-diazenes 7 (β=360–485×10−30 esu, T convention). Good to excellent thermal stabilities were also obtained for all azo dyes (235–317 °C). This multidisciplinary study showed that modulation of the optical and electronic properties can be achieved by introduction of the benzothiazole acceptor group in the thienylpyrrole system through position 2 or 6 of the benzothiazole heterocycle.

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