Enhanced third-order nonlinear optical properties of three 2D coordination polymers based on bis(imidazole) ligands and dicarboxylic ligands

Abstract

Reactions of transition metal acetates with dicarboxylic ligands and bis(imidazole) ligands afforded three coordination polymers, [Ni(1,2-BIB)(CEDA)]·1.5H2O 1, [Zn(1,2-BIB)(CADA)] 2 and [Zn2(1,4-BIB)2(CEDA)2]·2H2O 3, (1,2-BIB=1,2-bis((1H-imidazol-1-yl)methyl)benzene, H2CEDA=cyclohex-4-ene-1,2-dicarboxylic acid, H2CADA=cyclohexane-1,2-dicarboxylic acid, 1,4-BIB=1,4-bis((1H-imidazol-1-yl)methyl)benzene). Compounds 1 and 2 present a 2D rhombohedral grid sheet with the same topology. Compound 3 exhibits a (3, 4)-nodal 2D sheet with a point Schläfli symbol {4, 62}{4, 64, 8}. Z-scan experiments were carried out to evaluate the third-order nonlinear optical (NLO) performance of three compounds. The results show that they exhibit strong third-order NLO absorption in DMSO solution and thin films. The NLO absorptive coefficients β(MKS) in solution are evaluated to be 1.01×10−10mW−1 for 1, 0.42×10−10mW−1 for 2 and 0.46×10−10mW−1 for 3. The third-order NLO susceptibility χ(3) are calculated as 3.54×10−12esu for 1, 1.47×10−12esu for 2 and 1.61×10−12esu for 3. Interestingly, three compounds show much stronger NLO absorption in thin films with absorptive coefficients β(MKS) 6.41×10−5mW−1 for 1, 3.26×10−5mW−1 for 2 and 0.39×10−5mW−1 for 3. In addition, compound 2 exhibits strong self-focusing effects with γ 5.35×10−12m2/W. The corresponding third-order NLO susceptibility χ(3) are calculated as 1.03×10−5, 0.56×10−5 and 0.063×10−5esu, respectively. The composition of frontier orbitals of three compounds was investigated by using density functional theory (DFT). The influence of frontier orbitals on the third-order NLO properties was discussed.