DFT Studies For The Effect Of Ligand's Position,Type And Structure On Second-order Nonlinear Optical Properties Of Bis-cyclometalated Iridium(?) Complexes

Nonlinear optical?NLO?materials have received comprehensive researches because of the potential applications in optoelectronic adjustment,electro-optical switching,data storage and so on.Compared with inorganic materials,organic NLO materials have attracted significant attention due to the advantages in structural flexibility and faster response time.Among them,organometallic complexes can be effectively tuned the NLO response by modifying ligands,increasing metal atom and redox reaction.The iridium???complexes stand out from many metal complexes due to the unique luminescent characteristics and great NLO properties.Furthermore,Ir???complexes are easier for chemical modification to regulate their NLO properties.In this paper,the systematical density functional theory?DFT?and time-dependent DFT?TD-DFT?methods were selected to calculate a series of bis-cyclometalated Ir???complexes.And,we investigated the geometrical structures,HOMO and LUMO energy gaps,UV-Vis absorption spectra and second-order NLO properties.The main works are as follows:?1?The series of cationic[?2-phenylpyridine?₂?2,2'-bipyridine?Ir]⁺complexes were investigated.Through substituting the phenyl on different ligand's position to analyze the various NLO responses.When introducing the phenyl on 2-phenylpyridine ligands R₁ or R₂,the first hyperpolarizabilities(?_tot)can be enhanced.However,the second-order NLO response are obviously reduced by substituting phenyl on 2,2'-bipyridine R₃.The?_tot values are connected with the corresponding HOMO and LUMO energy gaps.The TD-DFT results show that the larger?_tot values are related to obvious charge transfer.?2?The novel synthesized nine complexes with various cyclometalated ligands?C^N?and aryl isocyanide ancillary ligands?CNAr?were calculated.By modulating the different electron-withdrawing or donating abilities ligands of C^N and CNAr,the geometric structures are nearly no changes,while the electronic properties varied obviously.With the enhancement of electron-withdrawing abilities,HOMOs and LUMOs energy levels display the decreasing trend,but?_tot values increase gradually.Tuning the types of ligands can effectively modulate the second-order NLO responses of studied systems.?3?The synthetic a family of Ir???complexes with different cyclometallated ligands?C^N?and ancillary ligands pyridine-2-carboxylate?pic?were selected to compute the second-order NLO properties.The results suggested that the degree of conjugation is significantly changed with the pic ligands varied which lead to the properties can be effectively modulated.Adjusting the C^N and pic ligands results in the change in energy difference between HOMOs and LUMOs.The TD-DFT conclusions indicate that the charge transfer obviously increased by introducing F atoms on studied complexes.Therefore,the F-C^N complexes own larger second-order NLO responses.