The photochromism of 1-alkyl-2-(arylazo)imidazoles embedded in micelles

• Photoisomerization of 1-alkyl-2-(arylazo)imidazoles, trans-to-cis, in micelle is reported.
• The rate increase in cation and neutral while decrease in anion micelle than free ligand state.
• The reverse, cis-to-trans has been carried out by thermal process.
• The quantum yield of trans-to-cis increases as per rate of photoisomerization.
• The Ea of cis-to-trans isomerization increases in presence of neutral and cation micelle.

Photochromism is dependent on the structure of material and matrix. 1-Alkyl-2-(arylazo)imidazole exists at ambient condition in trans-geometry about NN group. UV light irradiation in toluene solution of the compound has changed their trans structure to cis structure. These two isomers have different absorption spectra. The cis-to-trans isomerization proceeds slowly in visible light irradiation while it is appreciably fast with increasing temperature under thermal process. The rate of trans-to-cis isomerization is increased by 30–70% in presence of neutral (Triton-X-100) and cation (CTAB) micelle while anion micelle (SDS) reduces the same by 34–49%. The quantum yield of the photoisomerization is also increased by 33–84% in presence of neutral and cationic micelle. The activation energy (Ea) of cis → trans thermal isomerization is amplified in presence of Triton-X-100 and CTAB while it is decreased by adding SDS. Thus, the lowering of cis-to-trans thermal process in presence of neutral and cation micelle and increasing in SDS phase is justified.

UV light irradiation in toluene solution of 1-alkyl-2-(arylazo)imidazole has changed their trans structure to cis structure. The rate of trans-to-cis isomerization and quantum yields are increased in presence of neutral (Triton-X-100) and cation (CTAB) micelles while anionic micelle (SDS) reduces the same. The cis-to-trans isomerization proceeds slowly in visible light irradiation while it is appreciably fast in thermal process. The activation energy (Ea) of the process is calculated and in presence of Triton-X-100 and CTAB the Ea is increased. It justifies the reduction of thermal isomerization, cis-to-trans.Figure optionsDownload as PowerPoint slide