DFT Study On The Tunable Second-order Nonlinear Responses Of Ir(?) Complexes With C^N Ligands

Molecular chromophores with second order non linear optical(NLO) properties have attracted increasing interest for several decades owing to their potential utility in optical signal processing, data storage, laser technology and optical communication. Organometallic complexes have occupied an important role in the field of photophysics, electrochemistry, catalytic, organic light-emitting diodes, DNA structure probes, medicinal chemistry. Introducing the substituent groups, increasing the number of metal atoms and oxidating/reducting can change the charge transfer, thus tuning molecular ? values.The chelated 1,10-phenanthroline and N-arylazole metal Ir(?) complexes were investigated by quantum chemical calculations. The results show that:(1) The geometry structures, absorption spectra, the oxidation/reduction and the second-order NLO properties of Ir(?) complexes are investigated by density functional theory. The results indicate that different substituents have slightly affect on the structures of these complexes. The increasing conjugation of the substituents on the ancillary ligands makes their bond distances become more average. In the oxidation/reduction reaction, the bond length of the ancillary ligands change more with respect to chelating ligands. And significantly impacts the second-order NLO property, which is attributed to the changing of the charge transfer pattern and the increasing of charge transfer degree. In particular, the/3tot values of one-electron oxidized/reduced species(1a2+/la) are 75 times and 144 times larger than that of its eigenstate complex(1a+), respectively. For complex la+, the unconspicuous intraligand charge-transfer transition leads to a small NLO response. While for 1a2+ and la, the large second-order NLO responses are mainly related to the ligand-to-ligand charge-transfer transitions along with some ILCT transitions. The change of charge transfer pattern and the increase of charge transfer degree strongly affect th ?tot. As seen, the redox process of the cationic bis-cyclometalated iridium isocyanide complexes can effectively tune the second-order NLO properties.(2) The first hyperpolarizabilities(?vec) for mononuclear and dinuclear complexes with the substituted phenanthroline-5,6-dithiolate have been investigated by DFT. We also explore here the simplification of ligands, the number of metal atoms and redox process for computational expedience and the influence on ?vec. The research results suggest:Firstly, the use of simpler substituents(H,CH3) as models for dppe is largely trouble-free when computation is sought purely to address or to understand the structural properties of an organometallic complex but might present some problems where the focus is on ?vec. Secondly, the introduction of the Ni/Pt atom affects the sign of ?vec values, which attribute to the changing of the charge transfer direction. Thirdly,?vec value can be efficiently tuned in redox process and the redox-switchable NLO effects will come true. The ?vec value of these one-electron-oxidized/reduced species (2,2+,3,32+) is negative, which is different from mononuclear complex. As for the oxidized forms, the oxidization of mononuclear complex (12+), whose charge transfer direction is the same with eigenstate (1+) lead to the same sign of ?vec value. The others have the different charge transfer characteristics, which make the opposite sign of ?vec value. In contrast, for the reduction forms, whose charge transfer characteristics are different from the eigenstates lead to the opposite sign of ?vec value.