Contemporary Issues in Electron Transfer Research

Abstract

This is an overview of some of the important, challenging, and problematic issues in contemporary electron transfer research. After a qualitative discussion of electron transfer, its time and distance scales, energy curves, and basic parabolic energy models are introduced to define the electron transfer process. Application of transition state theory leads to the standard Marcus formulation of electron transfer rate constants. Electron transfer in solution is coupled to solvent polarization effects, and relaxation processes can contribute to and even control electron transfer. The inverted region, in which electron transfer rate constants decrease with increasing exoergicity, is one of the most striking phenomena in electron transfer chemistry. It is predicted by both semiclassical and quantum mechanical models, with the latter appropriate if there are coupled high- or medium-frequency vibrations. The intramolecular reorganizational energy has different contributions from different vibrational modes, which, in favorable cases, can be measured on a mode-by-mode basis by resonance Raman spectroscopy. Alternatively, mode-averaging procedures are available for including multimode contributions based on absorption or emission spectra. Rate constants for intramolecular electron transfer depend on electronic coupling and orbital overlap and, therefore, on distance. Mixed-valence systems have provided an important experimental platform for investigating solvent and structural effects and the transition between localized and delocalized behavior. One of the important developments in electron transfer is the use of absorption and emission measurements to calculate electron transfer rate constants. Ultrafast electron transfer measurements have been used to uncover nonequilibrium relaxation effects, an area that presents special challenges to the understanding of the dynamics and relaxation of the coupled processes. Electron transfer in the gas phase offers substantial insights into the nature of the electron transfer process. Similarly, electron transport in conductive polymers and synthetic metals depends on the basic principles of electron transfer, with some special nuances of their own.

Solvent as Electron Donor: Donor/Acceptor Electronic Coupling Is a Dynamical Variable

“…Partial atomic charges were obtained from the charge equilibration method of Rappé and Goddard 86 for the isolated single molecules and were fixed at the isolated molecule values for the trajectory. The dynamics run employed periodic boundary conditions with 50 DMA and one C152 in a box with dimensions that yield a density of 0.96 g/cm 3 (the density of DMA at 20°C). 87 Ewald sums with a convergence criterion of 2.5 × 10 -4 kcal/mol were used for van der Waals and Coulombic terms.…”

Optoelectronic and Semiconducting Properties of Conjugated Polymers Composed of Thiazolo[5,4-d]thiazole and Arene Imides Linked by Ethynylene Bridges

“…the molecular packing as well the conformation of a single molecule) controls the transport efficiency. 36 In the zero-limit, at high temperature and according to Marcus-Levich-Jortner (MLJ) model, 37,38 the hopping mobility can be modeled as a self-exchange chargetransfer (CT) reaction between neighboring molecules, and estimated through the Einstein-Smoluchoswki relation,…”

Push-pull effect on the geometrical, optical and charge transfer properties of disubstituted derivatives of mer-tris(4-hydroxy-1,5-naphthyridinato) aluminum (mer-AlND3)

“…Namely the band theory [74,75] and the hopping model [75][76][77][78][79][80][81][82][83] are widely used for describing the charge transport in organic materials. With the overlap of neighboring molecular orbitals the band is formed through which the conduction of the charge takes place according to the band theory model.…”