Design, synthesis, and characterization of the electrochemical, nonlinear optical properties, and theoretical studies of novel thienylpyrrole azo dyes bearing benzothiazole acceptor groups (original) (raw)

Keywords: Heterocyclic azo dyes Thienylpyrrole Benzothiazole Nonlinear optical (NLO) materials Reverse polarity First hyperpolarizability (b) Thienylpyrroles as auxiliary donors Redox properties Density functional theory (DFT) Thermal stability a b s t r a c t Two series of related donoreacceptor conjugated heterocyclic azo dyes based on the thienylpyrrole system, functionalized with benzothiazol-2-yl (5e6) or benzothiazol-6-yl acceptor groups (7) through an N]N bridge, have been synthesized by azo coupling using 1-alkyl(aryl)thienylpyrroles (1) and benzothiazolyl diazonium salts (2e4) 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/6-31þG(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 5e6 exhibit the largest first hyperpolarizabilities (b¼460e660Â10 À30 esu, T convention) compared to benzothiazol-6yl-diazenes 7 (b¼360e485Â10 À30 esu, T convention). Good to excellent thermal stabilities were also obtained for all azo dyes (235e317 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.