Kinetics and mechanism of bimolecular electron transfer reaction in quinone-amine systems in micellar solution

摘要

Photoinduced electron transfer (ET) reactions between anthraquinone derivatives and aromatic amines have been investigated in sodium dodecyl sulphate (SDS) micellar solutions.Significant static quenching of the quinone fluorescence due to high amine concentration in the micellar phase has been observed in steady-state measurements.The bimolecular rate constants for the dynamic quenching in the present systems kappa_q~(TR) as estimated from the time-resolved measurements,have been correlated with the free energy changes DELTAG~0 for the ET reactions.Interestingly it is seen that the kappa_q~(TR) vs DELTAG~0 plot displays an inversion behavior with maximum kappa_q~(TR) at around 0.7 eV,a trend similar to that predicted in Marcus ET theory.Like the present results,Marcus inversion in the kappa_q~(TR) values was also observed earlier in coumarin-amine systems in SDS and TX-100 micellar solutions,with maximum kappa_q~(TR) at around the same exergonicity.These results thus suggest that Marcus inversion in bimolecular ET reaction is a general phenomenon in micellar media.Present observations have been rationalized on the basis of the two-dimensional ET (2DET) theory,which seems to be more suitable for micellar ET reactions than the conventional ET theory.For the quinone-amine systems,it is interestingly seen that kappa_q~(TR) vs DELTAAG~0 plot is somewhat wider in comparison to that of the coumarin-amine systems,even though the maxima in the kappa_q~(TR) vs DELTAG~0 plots appear at almost similar exergonicity for both the acceptor-donor systems.These observations have been rationalized on the basis of the differences in the reaction windows along the solvation axis,as envisaged within the framework of the 2DET theory,and arise due to the differences in the locations of the quinones and coumarin dyes in the micellar phase.