title: Effect of PEG-200 and Tween-20 on photoisomerization of 1-alkyl-2-(arylazo)imidazoles in toluene.
abstract: 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 (E(a)) 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.
authors.affiliation: Department of Chemistry, Jadavpur University, Kolkata 700 032, India.
authors.forename: Pallab
authors.initials: P
authors.lastname: Gayen
authors.forename: Chittaranjan
authors.initials: C
authors.lastname: Sinha
mesh_terms: D045703:Emulsifying Agents / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry*; D007536:Isomerism; D055668:Photochemical Processes; D011092:Polyethylene Glycols / Q000737:chemistry*; D011136:Polysorbates / Q000737:chemistry*; D013816:Thermodynamics; D014050:Toluene / Q000737:chemistry; D014466:Ultraviolet Rays
chemical_list: D045703:Emulsifying Agents; D007093:Imidazoles; D011136:Polysorbates; D014050:Toluene; D011092:Polyethylene Glycols