Double helix chain frameworks constructed from bis-benzotriazole building blocks: Syntheses, crystal structures and third-order nonlinear optical properties

Reactions of 1,1′-(1,3-propylene)bis-1H-benzotriazole (pbbt) and KSCN with Ni(II) or Co(II) salt lead to the formation of two new double helix chain coordination polymers {[Ni(pbbt)2(NCS)2]·H2O}n1 and {[Co(pbbt)2(NCS)2]·H2O}n2. Their third-order nonlinear optical (NLO) properties were determined with a 7 ns pulsed laser at 532 nm. The results show that polymer 2 exhibits large NLO absorptive effects (α2 = 1.4 × 10−9 m W−1), and both of them show strong NLO refractive behaviors with the refractive index n2 of 3.02 × 10−18 m2 W−1 for 1 and 8.23 × 10−18 m2 W−1 for 2. The hyperpolarizability |γ| values of 1 and 2 were calculated to be 1.68 × 10−29 esu and 4.58 × 10−29 esu, respectively. This indicates that the third-order NLO properties of coordination polymers can be altered through metal ions manipulation.