Photoisomerisation of diethyloxadicarbocyanine iodide in micelles

Photoisomerisation of 3,3′-diethyloxadicarbocyanine iodide (DODCI) is studied in cationic (cetyl trimethyl ammonium bromide, CTAB), anionic (sodium dodecyl sulfate, SDS) and neutral (triton X-100, TX) micelles using picosecond emission spectroscopy. On addition of the surfactants to an aqueous solution of DODCI, above the critical micellar concentration, the emission quantum yield and lifetime of DODCI increase due to a marked decrease in the photoisomerisation rate. The retardation of the photoisomerisation process, is attributed to the high microviscosity at the micellar interface, compared to bulk water. Assuming that the Smoluchowski limit and the same `slipʹ/`stickʹ boundary condition hold for all three micelles, the effective microviscosities of the CTAB, SDS and TX micelles are estimated to be 70.0±20, 24.5±2 and 26.0±2 cP, respectively.