Intramolecular electron transfer in a linked viologen-quinone molecule: a rate constant study

Abstract

The authors synthesized a molecule MV{sup 2+}Q where a methylviologen (MV{sup 2+}) and a chloronaphthoquinone (Q) moiety are linked to each other via an aminoalkane (-NH(CH{sub 2}){sub 3}-) chain. Using the electron pulse radiolysis technique, they have determined rate constants for intra- and intermolecular electron transfer between electron donor and acceptor site of this molecule in water and sodium dodecyl sulfate (SDS) micellar solution. Measuring the decay of the absorbance at 605 nm as a function of the MV{sup 2+}Q concentration in water, they found a remarkably slow intramolecular electron transfer from the reduced methylviologen moiety to the quinone site (k{sub intra,water} = 1.4 {times} 10{sup 3} s{sup {minus}1}). Thus, even at very low MV{sup 2+}Q concentrations, intermolecular electron transfer (k = 3.8 {times} 10{sup 8} M{sup {minus}1}s{sup {minus}1}) was competing with the intramolecular reaction, and k{sub intra} was determined by extrapolation to zero MV{sup 2+}Q concentration.