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

• Main Author: Raposo, M. Manuela M.
• Publication Date: 2011
• Other Authors: Castro, M. Cidália R., Fonseca, A. Maurício C., Schellenberg, Peter Michael, Belsley, M.
• Format: Article
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: https://hdl.handle.net/1822/14627
• topic: Heterocyclic azo dyes; Thienylpyrrole; Benzothiazole; Push-pull systems; Reverse polarity; First hyperpolarizability (β); Hyper-Rayleigh scattering (HRS); Redox properties; Density functional theory (DFT); Thermal stability; Nonlinear optical (NLO) materials; First hyperpolarizability (beta); Thienylpyrroles as auxiliary donors; Science & Technology

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 N=N 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 ( = 460 - 660 x 10-30 esu, T convention) compared to benzothiazol-6-yl-diazenes 7 ( = 360 - 485 x 10-30 esu, T convention). Good to excellent thermal stabilities were also obtained for all azo dyes (235 - 317 oC). 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.