title: Photoisomerization of cyanine derivatives in 1-butyl-3-methylimidazolium hexafluorophosphate and aqueous glycerol: influence of specific interactions.
abstract: Photoisomerization of two cyanine derivatives, 3,3(')-diethyloxadicarbocyanine iodide (DODCI) and merocyanine 540 (MC 540), has been investigated in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate and aqueous glycerol (93 wt % glycerol +7 wt % water) by measuring fluorescence lifetimes and quantum yields. The aim of this work is to understand how the rates of photoisomerization of DODCI and MC 540 are influenced by specific solute-solvent interactions besides the viscosity of the medium. For DODCI, it has been observed that the nonradiative rate constants, which represent the rates of photoisomerization, are almost identical in the ionic liquid and aqueous glycerol at given temperature, indicating that viscosity is the sole parameter that governs the rate of photoisomerization. In contrast, the photoisomerization rate constants of MC 540 have been found to be a factor of 2 higher in aqueous glycerol compared to the ionic liquid. The observed behavior is due to the zwitterionic character of MC 540, a consequence of which, the twisted state gets stabilized by the solute-solvent hydrogen bonding interactions in aqueous glycerol, thus lowering the barrier for isomerization.
authors: Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India.
authors: K S
authors: KS
authors: Mali
authors: G B
authors: GB
authors: Dutt
authors: T
authors: T
authors: Mukherjee
mesh_terms: D002232:Carbocyanines / Q000737:chemistry* / Q000528:radiation effects; D005453:Fluorescence; D005990:Glycerol / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry; D007536:Isomerism; D008027:Light; D015394:Molecular Structure; D010777:Photochemistry; D011744:Pyrimidinones / Q000737:chemistry* / Q000528:radiation effects; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: C412621:1-butyl-3-methylimidazolium hexafluorophosphate; D002232:Carbocyanines; D007093:Imidazoles; D052578:Ionic Liquids; D011744:Pyrimidinones; D014867:Water; C018919:3,3'-diethyloxadicarbocyanine; C003954:merocyanine dye; D005990:Glycerol