Substituent and redox effects on the second-order NLO response of Ru(ii) complexes with polypyridine ligands: a theoretical study

Abstract

The geometric and electronic structures, redox properties, electronic absorption spectra, first hyperpolarizability, and dynamic hyper-Rayleigh scattering response of a series of Ru(II) complexes with polypyridine ligands have been investigated using density functional theory. The results illustrate that modifying ligands in four studied Ru(II) complexes have a slight influence on their structures, absorption spectra, and static first hyperpolarizabilities (β_tot) values, but the frontier molecular orbitals and charge transfer pattern are affected to some extent. However, one electron redox has a significant effect on the properties of complexes. Our calculations demonstrate that the maximum absorption wavelength exhibits a remarkable bathochromic shift and the related transition energy decreases for complexes 1^+/−–4^+/− compared with their intrinsic state complexes. The β_tot values of complexes 1^+/−–4^+/− are all enhanced and the largest β_tot value is observed for complex 4⁻, about 5.36 × 10⁵ a.u., which is 525.5 times as large as that of complex 4. The improvement of second-order NLO responses may be attributed to the extent of charge separation and direction/amount of charge transfer induced by gaining or losing one electron. We hope this work will be helpful for the future investigations of Ru(II) complex-based nonlinear optical materials.