Functionalized Ruthenium Dialkynyl Complexes with High Second-Order Nonlinear Optical Properties and Good Potential as Dye Sensitizers for Solar Cells

Various dipolar π-delocalized Ru­(II) dialkynyl complexes were prepared and characterized. Their second-order nonlinear optical (NLO) properties were investigated by the electric-field-induced second harmonic generation (EFISH) technique working in CH₂Cl₂ solution with an incident wavelength of 1907 nm, whereas the dipole moments were determined by density functional theory (DFT) calculations. All the investigated complexes are characterized by a negative value of μβ_1.907 EFISH, in agreement with a negative value of Δμ_eg (difference of the dipole moment in the excited and ground state) upon excitation. Their second-order NLO response can be easily modulated by the nature of the alkynyl substituents. Besides, the most promising “push–pull” ruthenium diacetylide complex, adequately functionalized for anchoring to TiO₂, was tested as photosensitizer in dye-sensitized solar cells (DSSCs).