Arylthienyl-vinyl-benzothiazoles as Efficient Second Harmonic Generators (SHG) for Nonlinear Optics ^†

New push-pull second harmonic generation (SHG) chromophores 2 were synthesized in order to study their linear and nonlinear optical properties. The donor-acceptor π-conjugated systems 2 were prepared in good to excellent yields by a simple aldol-type condensation of the precursor aldehydes 1 with 6-nitro-2-methyl-1,3-benzothiazole in the presence of NaOH. Hyper-Rayleigh scattering in dioxane solutions was used to evaluate their second-order nonlinear optical properties. The experimental results showed that the optical (linear and nonlinear) properties are influenced by the electron-donor strength of the groups of the π-conjugated bridge. The vinyl-benzothiazole derivative 2b, with methoxyl as the donor group, exhibited the largest first hyperpolarizability β (1660 × 10⁻³⁰ esu, 40 times greater than the standard reference pNA molecule) and the highest decomposition temperature (T_d = 360 °C). The good balance between nonlinearity and thermal stability makes this compound a promising candidate as second harmonic generator (SHG) for nonlinear optics.