The Second-order Nonlinear Optical Property Of The Chelated Polypyridyl Metal Ru(Ⅱ) Complexes

Chelated polypyridyl metal complexes have occupied an important role in the filed ofphotophysics, electrochemistry and DNA structure probes. They not only introduce thesubstituent groups, but also have good metal-ligand charge transfer character. Therefore, thechelated polypyridyl metal complexes become the NLO candidate material. Polypyridylligands, such as phenanthroline, bipyridyl, terpyridyl, diazafluorene, are a kind of πdelocalization nitrogen heterocyclic chelated ligands. The coordation of the ligands to themetal （chelation effect） make them to stay in the plane, thus enhancing the second-order NLOresponse.The chelated polypyridyl （1,10-phenanthroline and2,2′:6′,2′’-terpyridyl） metal Ru（Ⅱ）complexes were investigated by quantum chemical calculations. The results show that:（1） The dynamic first hyperpolarizabilities of a series of1,10-phenanthroline Ru（Ⅱ）complexes were calculated by coupled perturbed （time-dependent） method and DFT inN,N-Dimethylformamide （DMF） solution （λ=1.907μm）. Theβ_totvalues for Series acomplexes with two cis CO are less than those of Series b complexes with two trans PPh3.The increase of attracting electron ability and π-conjugation on the1,10-phenanthroline ligandleads to the increase of the correspondingβ_totvalues. TDDFT demonstrates that ILCTcontributes to theβ_totvalues for the complexes in Series a, while the relatively low-energyMLCT and LLCT are responsible for the complexes in Series b.（2）The static first hyperpolarizabilities for a series of the two-dimensional （2D） pincerRu（Ⅱ） complexes with the substituted Tpy and H₂SCS tridentate ligands （Tpy=2,2′:6′,2′’-terpyridyl and H₂SCS=2,6-bis（benzylaminothiocarbonyl）phenyl） have beeninvestigated by DFT and analytical third energy derivatives. The introduction of thedonor/acceptor groups affectsβ_totvalues of the2D systems, to a certain extent. Incomparison with system1[Ru（H₂SCS）（Tpy）]+, introducing the branches with strong electronacceptor group （p-NO₂-phenylethynyl） to the Tpy ligand or the branches with strong electrondonor group （p-NH₂-phenylethynyl） to the H₂SCS ligand can effectively improve theβ_totvalues. TDDFT show that theβ_totvalues are influenced by ILCT, MLCT, LMCT transitions.Moreover, the proton abstraction plays an important role in tuning the second-order NLOresponse. Particularly, for system5bearing the branches with NO2groups on H₂SCS ligand,there is a dramatic enhancement in theβ_totvalues for its deprotonated forms. Theβ_totvalues of the mono-deprotonated system5-H and the di-deprotonated system5-2H are58.712×10^-30esu and761.803×10^-30esu, about7.58times and36.4times compared with thedi-protonated system5, respectively. Theβ_totvalues in our work have two-dimensionalcharacter due to their large off-diagonal tensor values.