The effect of anionic, cationic and neutral surfactants on the photophysics and isomerization of 3,3 '-diethylthiacarbocyanine

The photophysical properties and isomerization of 3,3'-diethylthiacarbocyan ine (DTC) were studied in isooctane/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/water reverse micelles and in aqueous solutions containing sodium dod ecylsulfate (SDS), cetyltrimethylammonium bromide (CTAB) and chloride (CTAC ) and Triton X-100 (TX100) at concentrations below and above the critical m icelle concentrations (c.m.c.). The absorption and fluorescence spectra of DTC in AOT reverse micelles are red-shifted and the nonradiative deactivati on rate constant decreases strongly relative to that in water, leading to h igher fluorescence quantum yields (Phi (f)) and lifetimes. The DTC fluoresc ence decay in AOT reverse micelles and TX100 normal micelles is biexponenti al. SDS induces aggregation of DTC in water at concentrations well below th e c.m.c. (10(-5)-10(-3) mol l(-1)). Addition of SDS and TX100 at concentrat ions just above the c.m.c. increases steeply, while CTAB (or CTAC) exerts s uch an effect only at concentrations much higher than the c.m.c. A rise in the isomerization activation energy and the pre-exponent is observed in the reverse micelles with small w(o) (w(o) = [water]/[AOT]); the isomerization rate constant decreases in SDS, TX100 and CTAC micelles.