title: Bridge-mediated hopping or superexchange electron-transfer processes in bis(triarylamine) systems.
abstract: Hopping and superexchange are generally considered to be alternative electron-transfer mechanisms in molecular systems. In this work we used mixed-valence radical cations as model systems for the investigation of electron-transfer pathways. We show that substituents attached to a conjugated bridge connecting two triarylamine redox centres have a marked influence on the near-infrared absorption spectra of the corresponding cations. Spectral analysis, followed by evaluation of the electron-transfer parameters using the Generalized Mulliken-Hush theory and simulation of the potential energy surfaces, indicate that hopping and superexchange are not alternatives, but are both present in the radical cation with a dimethoxybenzene bridge. We found that the type of electron-transfer mechanism depends on the bridge-reorganization energy as well as on the bridge-state energy. Because superexchange and hopping follow different distance laws, our findings have implications for the design of new molecular and polymeric electron-transfer materials.
authors.affiliation: Institut für Organische Chemie, Bayerische Julius-Maximilians-Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany. lambert@chemie.uni-wuerburg.de
authors.forename: Christoph
authors.initials: C
authors.lastname: Lambert
authors.forename: Gilbert
authors.initials: G
authors.lastname: Nöll
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schelter