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

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 (beta(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 beta(tot) values of complexes 1(+/-)-4(+/-) are all enhanced and the largest beta(tot) value is observed for complex 4(-), about 5.36 x 10(5) 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.

Automated summary

This study investigated 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 using density functional theory. The results showed that modifying the ligands had a slight influence on the structures, absorption spectra, and static first hyperpolarizabilities of the complexes, but affected frontier molecular orbitals and charge transfer patterns to some extent. One electron redox significantly affected the properties of the complexes. The study demonstrated a remarkable bathochromic shift and decreased transition energy for the complexes with one electron redox compared to their intrinsic state complexes, indicating enhanced second-order nonlinear optical responses.