Intramolecular electron transfer in Cu(ii) complexes with aryl-imidazo-1,10-phenanthroline derivatives: experimental and quantum chemical calculation studies†
Abstract
1H-Imidazo[4,5-f][1,10]phenanthrolines containing phenyl (1), 4-(N,N-dimethylamino)phenyl (2), 4-(azadithiacrown-ether)phenyl (3), 3,4-dimethoxyphenyl (4) and 2,2′-bithiophen-5-yl (5) were synthesized and their Cu(II) complexes were studied to determine the effect of substituents, geometry of complexes and solvent nature on the spectral and redox properties of the copper complexes. It was found that in the case of 4-(N,N-dimethylamino)phenyl- and 4-(azadithiacrown-ether)phenyl substituents, the formation of a L2·Cu2+ complex of pseudo-tetrahedral geometry causes the appearance of an intense metal-to-ligand charge transfer (MLCT) band in the visible region and induces a positive shift in the reduction potential causing the occurrence of autoreduction of Cu(II). Density functional theory (DFT) and its extension to time dependent density functional theory (TD-DFT) were employed to study the molecular structure and electronic and spectroscopic properties of copper with the 4-(N,N-dimethylamino)phenyl-1H-imidazo[4,5-f][1,10]phenanthroline ligand (2). The calculation results are in agreement with those obtained from optical measurements. Electrochemical studies showed that the autoreduction is observed when Cu2+/Cu+ transfer and oxidation of the ligand occur under the closed electrochemical condition.
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