Second-order NLO properties of bis-cyclometalated iridium(Ⅲ) complexes: Substituent effect and redox switch

The iridium(III) complexes could be excellent second-order nonlinear optical (NLO) switch materials due to various advantages including abundant valence states, the diversity of coordination forms and rich electrochemical properties. In this work, the substituent effect and the multi-state switchable response of a series of novel Ir(CˆN)₂ADC complexes (CˆN = cyclometalated ligands and ADC = diaminocarbene), induced by electrochemical behavior, have been calculated by density functional theory. The results show that the introducing strong electron-withdrawing groups on ADC ligands significantly enhanced the static first hyperpolarizabilities (β_tot). Moreover, a distinct improvement of the β_tot values can be found from the neutral complexes to the corresponding redox states. By this way, the remarkable multi-state NLO switch can be achieved. Remarkably, the β_tot values of the one-electron-oxidized complex 1⁺ and the one-electron-reduced complex 1^- are ∼5.4 and ∼12.7 times larger than the corresponding neutral complex 1, respectively. The larger β_tot values are attributed to the lower transition energy and remarkable bathochromic shift of maximal absorption wavelength, which can be further illustrated by the separate distribution of β density. We envision that these studied iridium complexes can be seen as versatile and novel second-order NLO switching materials.