Kinetics and Yields of Electron Transfer in the Inverted Region

Abstract

The fluorescence dynamics of perylene in the presence of tetracyanoethylene in acetonitrile was studied experimentally and theoretically, taking into consideration that the quenching is carried out by remote electron transfer in the Marcus inverted region. The initial stage was understood as a convolution of the pumping pulse with the system response accounting for the fastest (kinetic) electron transfer accompanied by vibrational relaxation. The subsequent development of the process was analyzed with differential encounter theory using different models of transfer rates distinguished by their mean square values. The single channel transfer having a bell-shaped rate with a maximum shifted far from the contact produces the ground state ion pair. It was recognized as inappropriate for fitting the quenching kinetics at moderate and long times equally well. A good fit was reached when an additional near contact quenching is switched on, to account for the parallel electron transfer to the electronically excited state of the same pair. The concentration dependence of the fluorescence quantum yield is well fitted using the same rates of distant transfer as for quenching kinetics while the contact approximation applied to the same data was shown to be inadequate

Investigations of bimolecular photoinduced electron transfer reactions in polar solvents using ultrafast spectroscopy

“…The transient effect observed in the fluorescence decay of Pe* quenched by TCNE has been analysed using the differential encounter theory including the distance dependence predicted by Marcus theory [82]. The experimental data could only be reproduced by assuming two quenching pathways: a weakly exergonic one leading to the excited product and thus occurring at contact distance, and a highly exergonic one resulting to the ionic product in the electronic ground state and occurring at larger distance.…”

Hot recombination of photogenerated ion pairs

“…4 The bimolecular forward electron transfer ͑ionization͒ is universally described by the differential encounter theory ͑DET͒ equations, 1,24,25 …”

“…The quenching at early time proceeds at the kinetic regime and can be well described with a rate constant k 0 = k I ͑t =0͒. 4 At this stage, the initial equilibrium distribution of reactants in both q and r spaces is assumed not to be perturbed. This quantity can be calculated using Eq.…”

“…The fluorescence quenching dynamics of Pe after excitation by an ultrashort optical pulse was recently studied both experimentally and theoretically. 4 Using the abbreviations, D for Pe and A for TCNE, we consider a four-level energy scheme ͑Fig. 1͒ including vibrational sublevels ͑n =0, 1, 2, …͒ of the DA and D + A − states.…”

“…2͔. These ion pairs are born near contact, 4 at a distance where electron transfer ͑either forward or backward͒ is essentially limited by the solvent relaxation ͑1/ L ͒. These ion pairs undergo charge recombination to one of the vibrational states of the neutral products ͑dotted levels in Fig.…”