A new 2,2 ':6 ',2 ''-terpyridine-based ligand and its complexes: structures, photophysical properties and DFT calculations to evaluate the halogen effect on the TPA

A novel 2,2':6',2 ''-terpyridine-based ligand (L) and eight complexes have been synthesized and fully characterized. Six of these complexes ([CdLBr2](2)center dot CHCl3 (2), ZnLI2 (3), [CdLI2](2)center dot CH2Cl2 (4), ZnL(SCN)(2)center dot CHCl3 (5), [ZnL2](2)(ClO4)(4)center dot 7H(2)O (7) and [CdL2](ClO4)(2)center dot CH3OH (8)) were determined by single crystal X-ray diffraction analysis. Various weak interactions, including hydrogen bonds (C-H center dot center dot center dot N, C-H center dot center dot center dot X), C-H center dot center dot center dot pi and pi-pi interactions played significant roles in the final supramolecular structures. Linear and nonlinear optical properties of the ligand and eight complexes are described. Experimental results reveal that two-photon absorption (TPA) cross-sections of these complexes are extraordinarily larger than that of the ligand, with maximum values of 97, 661, 787, 218, 133, 613, 230, 384 and 241 GM for L and complexes 1-8 in DMF, respectively. Density functional theory (DFT) calculations were performed on 1-6 and revealed that the halogen affects the accepting capability of surrounding metals due to different electron inductive effects, in the order Br > SCN > I. Thus, this in turn affects the TPA cross-section values. The results indicate that the TPA crosssections vary in the order Br > SCN > I, which is consistent with the experimental results.