A series of novel metal complexes, ZnL2I2, CdL2I2, and HgL2I2 (L: 1-[Trans-4-(4-diethylaminostyryl) phenyl] imidazole), have been prepared and fully characterized. The structure of HgL2I2 was confirmed by single crystal X-ray diffraction analysis, which exhibits that Hg atom is coordinated by two iodine atoms and two nitrogen atoms from the ligand to form a distorted tetrahedral environment. The variable temperature H-1 NMR spectra proved that the metal complexes exhibit well stability in solution. Linear and nonlinear optical properties of them were described on the basis of density functional theory (DFT) calculations. Interestingly, we found that the complexation of the ligands with metal ion extends the electronic delocalization in the metal complexes, leading to dramatically enhanced two-photon absorption. (C) 2013 Elsevier B.V. All rights reserved.