Structure, electrochemistry and photochromism of [Cu(RaaiR′)(PPh3)X] (RaaiR′ = 1-alkyl-2-(arylazo)imidazole; X = Cl, Br, I) and correlation with theoretical calculations

Abstract

The reaction between CuX (X=Cl, Br, I), PPh3 and 1-alkyl-2-(arylazo)imidazole (RaaiR′) has synthesized [Cu(RaaiR′)(PPh3)X]. The composition has been established by spectroscopic (UV–Vis, IR, 1H NMR) data and the single crystal X-ray diffraction study of [Cu(MeaaiH)(PPh3)Cl] and [Cu(MeaaiH)(PPh3)Br] (MeaaiH=2-(p-tolylazo)imidazole) have confirmed the structures. These complexes show trans-to-cis (E-to-Z) photoisomerisation upon UV light irradiation. Quantum yields (ϕE→Z) of [Cu(RaaiR′)(PPh3)X] are lower than the free ligand values. The rate of isomerisation follows the sequence [Cu(RaaiR′)(PPh3)Cl]<[Cu(RaaiR′)(PPh3)Br]<[Cu(RaaiR′)(PPh3)I]. The cis-to-trans (Z-to-E) isomerisation is very slow upon light irradiation and has been achieved by a thermal route. The activation energy (Ea) of the Z-to-E isomerisation has been calculated by a controlled temperature reaction. DFT calculations of the optimized geometry of representative complexes have been used to determine the composition and energy of the molecular levels.