A DFT study of the second-order nonlinear optical properties of Ru(II) polypyridine complexes.

It is important to search for efficient nonlinear optical (NLO) materials due to their potential applications in electro-optic devices. Theoretical investigations into the second-order NLO responses of ten novel Ru(II) polypyridyl complexes based on [Ru(phen) 2 (bipy)] 2+ and [Ru(bphen) 2 (bipy)] 2+ have been performed using density functional theory. The effects on the second-order NLO response of introducing a substituent to the bipy group and of varying the ligand from phen to bphen are studied. The introduction of an electron-withdrawing/donating group improves the static first hyperpolarizability ( β tot ) for [Ru(phen) 2 (bipy)] 2+ derivatives, where the introduction of a strong electron-donating group, vinyl dimethylamine, increases the β tot value from 10 a.u. for an unsubstituted complex to 16 425 a.u. However, substituting the phen ligand for a bphen group has only a slight effect on the β tot values. Research into the electronic structures, UV-vis absorption spectra, and charge transfer properties was also carried out to further understand the second-order NLO properties of the ten complexes. The frontier orbital energy gap, electron density distribution, and charge-transfer direction and quantity are crucial elements impacting the second-order NLO responses of the complexes. Varying the electronic properties is considered to be an effective method for tuning the second-order NLO responses of materials. We hope our work will provide some helpful information for designing and synthesizing cost-effective and high-performance NLO materials.