Intercalated iodobismuthate in the layers of azoimidazoles. Structure, photochromism and DFT computation

[RaaiR′, RaaiR′H+]3 [Bi3I12]3− are obtained by refluxing BiI3 and RaaiR′ (1-alkyl-2-(arylazo)imidazoles) in a 2-methoxyethanol-methanol mixture. The X-ray structure determination of [MeaaiMe, MeaaiMeH+]3 [Bi3I12]3− (MeaaiMe = 1-methyl-2-(p-tolylazo)imidazole) has shown that the iodide bridged bismuthate(III) ([Bi3I12]3−) is intercalated in the channels formed by MeaaiMe-MeaaiMeH+. UV light irradiation in DMF solution of the compounds shows E-to-Z (trans-to-cis) isomerisation of the arylazoimidazole about the -NN- group. The reverse transformation, Z-to-E, is very slow with light irradiation, while it is induced by a thermal process. The quantum yield (ϕE→Z) of the E-to-Z isomerisation is dependent on the molar mass and rotor volume of the compounds. The activation energy (Ea) of the Z-to-E isomerisation is calculated by a controlled temperature experiment. DFT computations were performed to explain the spectra and the photochromism.