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The static second-order nonlinear optical (NLO) propertieson a series of the two-dimensional (2D) pincer Ru(II) complexes withthe substituted Tpy and H2SCS tridentate ligands (Tpy =2,2′:6′,2″-terpyridyl and H2SCS =2,6-bis(benzylaminothiocarbonyl)phenyl) have been investigated bydensity functional theory (DFT). Introducing different donor/acceptorsubstituents to two ligands has an influence on the static first hyperpolarizabilities(βtot) of the 2D systems. Compared to the referencesystem 1[Ru(H2SCS)(Tpy)]+, introducingthe branches with strong electron acceptor group (p-NO2-phenylethynyl) to the Tpy ligand or the brancheswith strong electron donor group (p-NH2-phenylethynyl) to the H2SCS ligand can effectively improvethe βtotvalues. Time-dependent DFT (TDDFT) calculationsindicate that the enhanced βtotvalues of the substitutedsystems are dominated by the intraligand charge transfer (ILCT), metal-to-ligandcharge transfer (MLCT) and ligand-to-metal charge transfer (LMCT)transitions. Furthermore, the proton abstraction plays an importantrole in tuning the second-order NLO response. Particularly, for system 5bearing the branches with NO2groups on H2SCS ligand, there is a dramatic enhancement in the βtotvalues for its deprotonated forms. The βtotvalues of the monodeprotonated system 5-Hand the dideprotonatedsystem 5-2H(58.712 × 10–30and761.803 × 10–30esu) are about 7.58 times and36.4 times larger than their diprotonated system 5, respectively.The second-order NLO responses based on substituent effect and protonabstraction switch are two-dimensional in characteristic with thelarge off-diagonal tensor values. [ABSTRACT FROM AUTHOR]

The second-order nonlinear optical (NLO) properties of a series of Pt(II) dithienylethene (DTE) complexes possessing the reversible photochromic behavior have been investigated by density functional theory (DFT) combined with the analytic derivatives method. The results show that the calculated static first hyperpolarizabilities (βtot) of the open-ring and closed-ring systems significantly increase in the range of 2.1-4.5 times through strengthening of the electron-withdrawing ability of the substituent R (R = H, CF3, NO2) and an increase of the number of thiophene rings. Moreover, there is a large enhancement of the βtot values from the open-ring systems to the corresponding closed-ring systems. This efficient enhancement is attributed to the better delocalization of the π-electron system, the more obvious degree of charge transfer, and the larger f(os)/E(gm)(3) (f(os) is the oscillator strength, and E(gm) is the transition energy between the ground and the excited states) values in the closed forms according to the bond length alternation (BLA) and time-dependent density functional theory (TDDFT) calculations. In addition, the dispersion has less influence on the frequency-dependent first hyperpolarizabilities (βtot(ω)) of the studied systems at the low-frequency area ω (0.000-0.040 au). Our present work would be beneficial for further theoretical and experimental studies on large second-order NLO responses of metal complexes.