Terpyridine derivatives functionalized with (hetero)aromatic groups and the corresponding Ru complexes: synthesis and characterization as SHG chromophores

Abstract

Push–pull terpyridine derivatives were synthesized and characterized in order to study the variations produced in their optical and electronic properties by linking different (hetero)aromatic electron donor moieties at position 4 of the electron deficient terpyridine moiety. The final donor-acceptor systems were synthesized in fair to good yields by Kröhnke condensation of the precursor aldehydes, with 2-acetylpyridine. Hyper-Rayleigh scattering in dioxane solutions using a fundamental wavelength of 1064 nm was employed to evaluate their second-order nonlinear optical properties. Terpyridine derivative functionalized with the 9-ethyl-9H-carbazolyl group exhibited the largest first hyperpolarizability (beta = 610 × 10-30 esu, using the T convention) thus indicating its potential application as a second harmonic generation (SHG) chromophore. Terpyridine derivatives were also used as ligands for the synthesis of novel [RuII(tpy)(NCS)3]– complexes, prepared in good yields by a two-step procedure involving the preparation of [RuIII(tpy)(Cl3] as precursors. RutheniumII complexes display a broad absorption in the visible range, accounting for their very dark color. Their redox behaviour is mainly characterized by the RuII-RuIII oxidation and by the ligand-centred reduction, whose potentials can be finely tuned by the electronic properties of the aromatic substituents on the terpyridine ligand. Hyper-Rayleigh scattering in methanol solutions using a fundamental wavelength of 1064 nm was also employed to evaluate their second-order nonlinear optical properties.