DFT Theoretical Studies On Second-order Nonlinear Optical Properties Of Iridium Complexes By Cyclometallic Ligands And Redox

During the past few decades,people have been studying new organic and metal complex materials with nonlinear optical（NLO）characteristics to design and synthesize NLO materials with low cost and high comprehensive performance,which are used in high-efficiency photonics and electro-optical devices.Among them,bis-cyclometalated iridium（Ⅲ）complexes with excellent NLO response in terms of photophysics and redox properties have attracted considerable attention,and they are expected to find applications in high-efficiency photonics and electro-optical devices.This paper used density functional theory（DFT）to calculate some bis-cyclometalated iridium（Ⅲ）complexes.And the geometric and electronic structures,redox centers,UV-vis absorption spectra and second-order NLO properties of these complexes have been investigated.At the same time,the effects of changing the ligands and having redox progress on the second-order NLO response are also discussed.The research contents are as follows:1.A series of iridium（Ⅲ）complexes were calculated,through substituting trifluoromethyl and nitro groups at different ligands and redox process to analyze the NLO responses.The first hyperpolarizability(β_tot)value by substitution of electron-withdrawing nitro group on the ancillary ligand is 4.8 times larger than that substitution with the trifluoromethyl.This indicates that the enhancement of electron-absorbing ability will increase theβ_tot value.Iridium（Ⅲ）complexes have redox process and the redox center is usually on the ancillary ligand,which makes the direction of charge transfer change significantly.At the same time,the remarkable bathochromic shift of maximal absorption in the redox process is obvious,and it can significantly improve the NLO response,which is consistent with the results calculated by the super rayleigh scattering（HRS）method.2.Three bis-cyclometalated iridium（Ⅲ）complexes withβ-diketiminate ancillary ligand were calculated,the redox process had little effect on bond angle and bond length,and the different ligands had little effect on the configuration.Theβ_tot value was not affected by changing theβ-diketiminate ancillary ligand,but the second-order NLO response of iridium complex was obviously enhanced by the redox process.Theβ_tot values of oxidation states complexes 1⁺,2⁺and 3⁺are about 10.2,19.7 and 25.5times larger than their corresponding neutral complexes,respectively.And theβ_totvalues of reduction states complexes 1^-,2^-and 3^-are about 13.2,35.0 and 8.5 times larger than neutral complexes,respectively.Due to the obvious red-shifted of the maximum absorption wavelength and the decrease of the related transition energy with the redox states iridium（Ⅲ）complexes,their first hyperpolarizability are larger than the neutral complexes.