Computation Studies On Second-Order Nonlinear Optical Properties Of Ruthenium(Ⅱ)/Rhodium(Ⅲ) Complex

In recent decades,organometallic complexes have been widely used in molecular electronics and photonics due to their diversity of structures and properties.Among them,Ru（Ⅱ）and Rh（Ⅲ）complexes show the advantages of environmental stability,high transparency and easy modification and regulation,which make them become a kind of promising NLO materials,and have attracted great attention of scientific researchers.In this paper,the structures and properties of a series of transition metal Ru（Ⅱ）and Rh（Ⅲ）complexes with electronic configuration of d⁶ are calculated based on density functional theory（DFT）and time-dependent density functional theory（TD-DFT）.The geometric and electronic structures,frontier molecular orbitals,redox center,UV-Vis spectra,electronic transition properties and second-order NLO properties of these studied systems have been discussed in depth.The main research contents as follows:（1）A series of Ru（Ⅱ）complexes with polypyridine ligand have been investigated by means of DFT,and the effects of modified ligand and redox on the second-order NLO properties of these complexes have been analyzed.The results illustrate that theβ_tot values of complexes[Ru（dpma）（bpy）（dppn）]²⁺and[Ru（bpy）₂（dppn）]²⁺increased with the extension of ligand molecular skeleton,which is consistent with their smaller E_gapvalues.Theβ_tot values of redox state complexes are all enhanced compared with their corresponding intrinsic state complexes,and the reduced species has more significanfly improved than those of oxidized species.The obtainedβ_tot values of complexes[Ru（dppz）（bpy）₂]⁺and[Ru（bpy）₂（phen）]⁺about 5.36×10⁵a.u.and 9.21×10⁴a.u.,which are 525.5 and 1024.5 times as large as that of their corresponding intrinsic state complexes respectively.The TD-DFT calculation results demonstrate that the improvement ofβ_tot values may be attributed to the redshift of the maximum absorption wavelength,the decrease of related transition energy,and the more obvious extent of charge separation.（2）The static first hyperpolarizabilityβ_tot,static and dynamicβ_HRSvalues of a series of metal Rh（Ⅲ）complexes have been calculated by DFT.The effects of substituents on second-order NLO properties of these complexes are investigated.The results show that the introduction of a strong electron-donating/withdrawing group（-NMe₂/-NO₂）on the R₃ substituent in the dpqx ligand increased theβ_tot values of complex[Rh（dpqx）₂（Ph COCHCOPh）]by 78 and 37 times.Moreover,switching the positions of R₁（-Ph）and R₂（-H）substituents in the other chelated ligand,theβ_tot value increased by about 15 times.The variety of R₂ substituents is also accompanied by the increase ofβ_tot value,but the amplitude is not large（1.6 and 4.3 times）.In addition,the static,dynamicβ_HRS values andβ_tot values of the discussed complexes show the same variation trend.It is found that the complex exhibits a large second-order NLO response due to an increase in the degree of charge transfer during the electron transition and a remarkable bathochromic shift in the maximum absorption wavelength.