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

Abstract

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·CHCl₃ (2), ZnLI₂ (3), [CdLI₂]₂·CH₂Cl₂ (4), ZnL(SCN)₂·CHCl₃ (5), [ZnL₂]₂(ClO₄)₄·7H₂O (7) and [CdL₂](ClO₄)₂·CH₃OH (8)) were determined by single crystal X-ray diffraction analysis. Various weak interactions, including hydrogen bonds (C–H⋯N, C–H⋯X), C–H⋯π and π–π 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 cross-sections vary in the order Br > SCN > I, which is consistent with the experimental results.