Effect of PEG-200 and Tween-20 on photoisomerization of 1-alkyl-2-(arylazo)imidazoles in toluene

The photoisomerization of 1-alkyl-2-(arylazo)imidazole, trans-to-cis, has been studied in the matrix of PEG-200 and Tween-20 in toluene medium by UV light irradiation. The trans and cis-isomers have different absorption spectra. The cis-to-trans isomerization proceeds slowly in visible light irradiation while it is appreciably fast in thermal process. The rate of trans-to-cis isomerization is decreased by 30–60% in presence of PEG-200 and Tween-20. The quantum yield of the photoisomerization is also decreased by 35–55% and follows the rate sequence: free state > PEG-200-phase > Tween-20 phase. The activation energy (Ea) of cis → trans, thermal backward isomerization, is reduced in PEG-200 and Tween-20 phase following free state > PEG-200-phase > Tween-20-phase. The branched polyhydroxo structure of Tween-20 may help to wrap the polar photochrome more efficiently than major ether functionalized PEG-200 and stabilizes trans-isomer.

The photoisomerization of 1-alkyl-2-(arylazo)imidazole in presence of PEG-200 and Tween-20, in toluene solution by UV light irradiation has been reported. The rate and quantum yields of trans-to-cis isomerization are decreased in presence of microemulsion. The cis-to-trans isomerization is carried out by thermal route. The activation energy (Ea) follows as free state > PEG-200-phase > Tween-20-phase. The branched polyhydroxo structure of Tween-20 may help to wrap the polar photochrome more efficiently than major ether functionalized PEG-200 and stabilizes trans-isomer.Figure optionsDownload as PowerPoint slideHighlights
► Photoisomerization of 1-alkyl-2-(arylazo)imidazoles, trans-to-cis, in PEG-200 and Tween-20 is reported.
► The rate and quantum yields increase in emulsion and follows free state < PEG-200-phase < Tween-20-phase.
► The reverse, cis-to-trans has been carried out by thermal process.
► The Ea of cis-to-trans isomerization follows: free state > PEG-200-phase > Tween-20-phase.