DFT Study on the Second-Order NLO Responses of 2-Phenyl Benzoquinoline Ir(III) Complexes by Substituents and Redox Effects.

Metal complexes have received extensive attention in nonlinear optical (NLO) materials because of their advantages, such as shorter response times and more flexible structural properties. Density functional theory is used in investigating the geometric structures, electronic structures, charge centroid, and first hyperpolarizability (β) of a series of selected 15 coordinated Ir(III) complexes. The substitute effect and one-electron redox process effects on the structures and properties of 15 coordinated Ir(III) complexes are considered. When the electron-withdrawing group is introduced into the ligand, the HOMO-LUMO energy gap decreases and the β value increases, positively correlating with the electron-withdrawing ability. The single electron redox process can also improve the NLO responses of complexes, especially the reduction process. The β value of complex 4 is the largest, 2078 times higher than that of complex 4. The analysis shows that the variation of NLO responses of complexes is ascribed to the change of electronic structures and the charge transfer modes induced by the ligand modification and redox process, which are considered to be two effective methods in enhancing the NLO responses of 2-phenyl benzoquinoline Ir(III) complexes. This study aims to offer design insights into high-performance nonlinear optical materials.