η5-Monocyclopenta¬dienylmetal(II) complexes with thienyl acetylide chromophores: synthesis, electrochemical studies and first hyperpolarizabilities

A series of η5-monocyclopentadienylmetal(II) complexes with nitro-substituted thienyl acetylide ligands of general formula [M(η5-C5H5)(L)(C≡C{C4H2S}nNO2)] (M=Fe: L= k2-DPPE (n= 1, 2; M=Ru: L= k2-DPPE, 2 PPh3, n= 1, 2; M=Ni: L=PPh3, n= 1, 2) has been synthesized and fully characterized by NMR, FT-IR and UV–Vis spectroscopies. The electrochemical behavior of the complexes was explored by cyclic voltammetry. Quadratic hyperpolarizabilities () of the complexes have been determined by hyper-Rayleigh scattering (HRS) measurements at 1500 nm. The effect of donor abilities of different organometallic fragments on the quadratic hyperpolarizabilities was studied and correlated with spectroscopic and electrochemical data. Density functional theory (DFT) and time dependent DFT (TDDFT) calculations were employed to get a better understanding of the second-order nonlinear optical properties in these complexes. In this series, the complexity of the push-pull systems is revealed even so several trends in the second-order hyperpolarizability can still be recognized. In particular, the overall data seem to indicate that the existence of other electronic transitions besides the main MLCT, clearly control the effectiveness of the organometallic donor ability on the second-order NLO properties of these push-pull systems.