Redox-switching second-order nonlinear optical responses of N^N^N ruthenium complexes

The second-order nonlinear optical (NLO) properties of ruthenium complexes, including redox-active iminoquinonoid, quinonoid, and dithiolene noninnocent ligands, have been investigated using density functional theory (DFT) combining with the finite field (FF) method. The DFT–FF calculations show that these complexes have excellent second-order NLO responses. According to B3LYP/B3P86/CAM-B3LYP/6-31G(d) calculations complex 3e1reduced has the largest β value among all the complexes studied. The calculations show that the β value of 3e1reduced is ∼7.7 times, ∼10.6 times and ∼11.6 times larger than those of 2e1reduced, 1e1reduced and 1, respectively. Complex 1 can act as the multi-state redox NLO switchable materials through sequential one-electron reduced processes.