Computational study: how redox affect the nonlinear optical properties of donor substituted heteroleptic bis-tridentate Ru(II) complexes?

Donor substituted heteroleptic bis-tridentate Ru(II) complexes with different deprotonated forms exhibit larger alterations of the first hyperpolarizabilities in oxidized process and are promising to become redox-switchable nonlinear optical (NLO) molecular materials. For systems with diprotonated form, the β(vec) value of the two-electron-oxidized system ¹3²⁺ is 5.3 and 178.6 times as large as those of the reduced parent 3 and the one-electron-oxidized system 3⁺ according to the DFT-FF results. For systems with mono-protonated form, the oxidization of the deprotonated benzimidazole anion is more helpful to enhance the β(vec) value because of the increasing β(x) component. For systems with fully deprotonated form, the largest ratio of |β(vec)((1″)⁺)/β(vec)(1″)| of the system without substituent is about 13.2 due to the dominant off-diagonal tensor β(zxx). And the time-dependent density functional theory (TDDFT) results indicate that the charge transfer transition of the first excited state displays an indispensable role for larger off-diagonal tensor. Finally, the calculated frequency-dependent β results exhibit a small dispersion effect at the low-frequency region.