Synthesis, spectroscopic characterization, photochromism of zinc(II)-iodo complexes of long chain 1-alkyl-2-(arylazo)imidazoles and the DFT correlative studies

Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata-700 032, India

E-mail : c_r_sinha@yahoo.com

Manuscript received online 22 July 2014, accepted 26 August 2014

Zinc(II)-iodo complexes of 1-alkyl-2-(arylazo)imidazole (1-5), [Zn(Raai-C_nH_2n+1)₂ I₂ ] (6-10) (Raai-C_nH_2n+1, n = 10 (1/6), 12 (2/7), 14 (3/8), 16 (4/9), 18 (5/10)) have been characterized by spectroscopic studies (FT-IR, UV-Vis, ¹H NMR). The complexes, [Zn(Raai-C_nH_2n+1)₂ I₂ ], exhibit UV light assisted photoisomerisation (E(trans)-to-Z(cis)) in the solution phase. The Z-to-E (cis-to-trans), isomerisation is very slow with visible light irradiation and has been carried out under thermal treatment. The rate and quantum yield of photochromism are dependent on molar mass and chain length of -C_nH_2n+1. The activation energy (E_a ) is also lower in the complexes than free ligand data. The spectral properties have been explained using DFT computation of optimized geometries of [Zn(Haai-C₁₀H₂₁)₂ I₂ ].