Excited-state torsional relaxation in 1,1′-dihexyl-3,3,3′,3′-tetramethylindocarbocyanine iodide: Application to the probing of micelle structure

Abstract

The excited-state torsional relaxation of 1,1′-dihexyl-3,3,3′,3′-tetramethylindocarbocyanine iodide (DHICC) has been studied by fluorescence lifetime and quantum yield measurements. The results show that the viscosity dependence of the excited-state barrier crossing conforms to the Smoluchowski limit of Kramers' equation. The viscosity dependence of the fluorescence quantum yield and lifetime of DHICC can be used to assess the effective microviscosity of sodium dodecyl sulfate micelles. While both the radiative and nonradiative rates of DHICC change on attachment to SDS micelles, the rise in quantum yield is mainly the result of a marked decrease in the nonradiative rate. Experiments with un..