Rate constants of the thermal cis-trans isomerization of azobenzene dyes in solvents, acetone/water mixtures, and in microheterogeneous surfactant solutions
✍ Scribed by Kathrin Gille; Helmut Knoll; Konrad Quitzsch
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 217 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0538-8066
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✦ Synopsis
Rate constants k iso of the thermal cis-trans isomerization of four 4,4'-nitro-aminoazobenzenes with different amino groups have been determined in homogeneous aprotic solvents and polyglykol oligomers, primarily by means of conventional flash photolysis. The rate constants have been correlated with polarity (according to max from UV/Vis absorption spectra of the trans isomers) and bulk viscosity of the solvents. Qualitative conclusions about the influence of varying concentrations of water with respect to polarity and hydrogen bonding on k iso -and max -values in acetone/water mixtures were derived. Based on these results the data from microheterogeneous solutions have been interpreted.
In microheterogeneous water/surfactant solutions k iso -values of selected azo dyes were strongly dependent on the concentrations of SDS, Triton ᭨ X-100, C 12 EO 8 in water, and varied with the composition of bicontinuous microemulsions of Igepal ᭨ CA-520/ heptane/water. The large spread of isomerization rate constants is in part due to varying microviscosity.
Replacement of H 2 O by D 2 O in aqueous surfactant solutions produced surprisingly large kinetic solvent isotope effects.