Mechanistic discrimination of the reaction of 1-aminopyrene cation radical using an electron transfer stopped-flow method. Decay reaction accelerated by neutral molecules

Abstract

Using an electron transfer stopped-flow (ETSF) method, the decay kinetics of 1-aminopyrene cation radical (AP + ) in acetonitrile was studied. When AP + was formed quantitatively via the electron transfer with tris( p-bromophenyl)amine (TBPA) cation radical, it was found that the decay reaction proceeded according to a rate law of −d[AP + ]/d t= k[AP + ] 2, indicating the cation radical–cation radical coupling (RRC) mechanism. In contrast, in the presence of AP, the decay reaction was accelerated remarkably, and the kinetics has been changed to adhere to a rate law of −d[AP + ]/d t= k[AP + ] 2[AP], which indicated the two step interactions as follows: AP + + AP⇌( AP) 2 + ( AP) 2 + + AP + →( AP + ) 2+ AP While the reactions of aromatic amine cation radicals have been revealed as the RRC mechanism mainly, the present type of interaction can be regarded as a possible reaction mechanism of cation radicals, and would be important to control the formation of conducting polymer materials. The ETSF method has permitted the clarification of the effect of the neutral molecules on the reaction kinetics of cation radicals, which would be very difficult to reveal using electrochemical techniques.