Fluorescence Quenching due to Photo-induced Charge Transfer in Aqueous Miceliar Solutions and Structures of Micelles

Abstract

Fluorescence behaviors of typical heteroexcimer systems in aqueous micellar solutions have been studied for the understanding of the mechanisms of photochemical charge transfer proces-ses in micellar solutions. Results obtained have been examined in comparison with those obtained for homogeneous solutions. Fluorescers such as pyrene, various pyrend derivatives and several other aromatic hydrocarbon systems, and quenchers such as N, N-dimethylaniline, sodium p- (dimethylamino) benzenesulfonate, dicyanobenzenes and 4-cyanopyridine were used. It was found that the aromatic hydrocarbon fluorescence was strongly quenched by those quen-chers, that the relation between the fluorscence yield and the quencher concentration greatly deviated from the simple Stern-Volmer equation and that the fluorescence decay curves under the presence of quenchers were not exponential. In all cases examined here, no heteroexcimer fluorescence was observed. The effect of the concentration of qtienchers on the relative fluo-rescence yields and on the fluorescence decay can be well interpreted under the assumptions that the quenchers are distributed over both micellar and bulk aqueous phases and that the distribution in the micellar phase obeys the Poisson statistics. This analysis shows that the fluorescence quenching in the heteroexcimer systems in, micellar solutions involves both the first order reaction process due to the charge transfer between the fluorescer and quencher trapped in the same micelle and the second order reaction process due to the interaction between the fluorescer trapped in the micelle and the quencher from the bulk aqueous phase. No generation of the heteroexcimer fluorescence for various aromatic hydrocarbon-N, N-dimethylaniline sys-tems including (1-pyreny1)-(CH₂)n-COOH (n=1-11), suggests that the interior of micelles is not composed of aliphatic hydrocarbon-like substances and that it has a very high polarity and a large amount of water. This is quite different from the behavior of bilayer liposomes in which a pyrene-N, N-dimethylanilne system shows heteroexcimer fluorescence.