Behavior of radical ion pairs produced by photoinduced electron transfer in polar solutions : Their dynamics in picosecond-hundred nanosecond regime

Abstract

The dynamic behavior of radical ion pairs in polar solvents has been studied by directly observing time-resolved transient absorption spectra in the picosecond-hundred nanosecond regime and also by observing the picosecond laser induced photocurrent. Pyrene-N.N-dimethylaniline, pyrene- p-dicy-anobenzene, pyrene-triethylamine exciplex systems and the excited state of pyrene-pyromellitic dian-hydride electron donor-acceptor complexes in polar solvents have been examined. It has been clearly demonstrated that the rate constant k n, of the charge recombination deactivation of radical ion pairs shows a strong dependence upon the energy gap Δ G ip, (between the ion pair and the neutral ground state) and upon the molecular nature of individual electron donor or acceptor ions. The plot of k nvs Δ G ip for the chemically similar π-π exciplex systems as well as singlet excited electron donor-acceptor complex systems studied in this and some previous works showed clearly the characteristic features of the so-called Marcus inverted region.