Synthesis, structure, photochromism and DFT calculations of copper(I)-triphenylphosphine halide complexes of thioalkylazoimidazoles

[Cu(SRaaiNR′)(PPh3)X] complexes are synthesized by the reaction of CuX (X = Cl, Br, I), triphenylphosphine and 1-alkyl-2-[(o-thioalkyl)phenylazo]imidazole (SRaaiNR′). The single crystal X-ray structure of [Cu(SEtaaiNH)(PPh3)I] (SEtaaiNH = 2-[(o-thioethyl)phenylazo]imidazole) shows a distorted tetrahedral geometry of the copper center with bidentate, N(azo), N(imidazole) chelation of SEtaaiNH and coordination from PPh3 and iodine. These complexes show a trans-to-cis isomerization upon irradiation with UV light. The reverse transformation, cis-to-trans isomerization, is very slow with visible light irradiation and is thermally accessible. The quantum yields (ϕt→c) of the trans-to-cis isomerization of [Cu(SRaaiNR′)(PPh3)X] are lower than the free ligand values. This is due to the increased mass and rotor volume of the complexes compared to the free ligand data. The rate of isomerization follows the order: [Cu(SRaaiNR′)(PPh3)Cl] < [Cu(SRaaiNR′)(PPh3)Br] < [Cu(SRaaiNR′)(PPh3)I]. The activation energy (Ea) of the cis-to-trans isomerization is calculated by a controlled temperature reaction. DFT computation of representative complexes has been used to determine the composition and energy of the molecular levels.

The complexes [Cu(SRaaiNR′)(PPh3)X] (X = Cl, Br, I and SRaaiNR′ = 1-alkyl-2-[(o-thioalkyl)phenylazo]imidazole) have been reported. The structure of [Cu(SEtaaiNH)(PPh3)I] (SEtaaiNH = 2-[(o-thioethyl)phenylazo]imidazole) shows a distorted tetrahedral geometry of the copper. A trans-to-cis isomerization of the complexes upon UV-light irradiation is observed. The reverse transformation, cis-to-trans isomerization, is also a thermal process. The rate of isomerization follows: [Cu(SRaaiNR′)(PPh3)Cl] < [Cu(SRaaiNR′)(PPh3)Br] < [Cu(SRaaiNR/) (PPh3)I]. The activation energy (Ea) of the photoisomerization is lower in the complexes than for the free ligand. DFT computations have been used to determine the composition and energy of the molecular levels for an explanation of spectra, redox properties and photoisomerization.Figure optionsDownload as PowerPoint slideResearch highlights
► The chemistry of copper(I) complexes of thioalkylazoimidazoles is described.
► The structure of the complexes are described by spectroscopic studies and X-ray crystallography.
► Redox properties are examined by cyclic voltammetry.
► DFT computation is used to correlate experimental results and calculated data.
► The freeligand and complexes under go cis-trans photoisomerisation upon light irradiation with UV light.
► The rate of transformation is dependent on the rotor mass, rotor volume and nature of the substituent.