Ion-Mediated Electron Transfer in a Supramolecular Donor-Acceptor Ensemble

Abstract

Ion binding often mediates electron transfer in biological systems as a cofactor strategy, either as a promoter or as an inhibitor. However, it has rarely, if ever, been exploited for that purpose in synthetic host-guest assemblies. We report here that strong binding of specific anions (chloride, bromide, and methylsulfate but not tetrafluoroborate or hexafluorophosphate) to a tetrathiafulvalene calix[4]pyrrole (TTF-C4P) donor enforces a host conformation that favors electron transfer to a bisimidazolium quinone (BIQ2+) guest acceptor. In contrast, the addition of a tetraethylammonium cation, which binds more effectively than the BIQ2+ guest in the TTF-C4P cavity, leads to back electron transfer, restoring the initial oxidation states of the donor and acceptor pair. The products of these processes were characterized via spectroscopy and x-ray crystallography.

Spin Chemistry Investigation of Peculiarities of Photoinduced Electron Transfer in Donor–Acceptor Linked System

“…), thermal and photoinduced transformations of organic compounds [1][2][3]. To date, a detailed study of the photoinduced electron transfer processes (PET) has been made, in particular, the effect of factors such as the electronic structure of the donor and the acceptor, the polarity of the medium, and the excitation energy [4].…”

Supramolecular electron transfer-based switching involving pyrrolic macrocycles. A new approach to sensor development?

“…As detailed below, we found that by using a mixture of the electron donating tetrathiafulvalene-appended calix [4]pyrrole (TTF-C4P) 21 with the dicationic electron acceptor bisimidazolium quinone (BIQ 2+ ) 22 we could reversibly switch the direction of electron transfer by varying the surrounding ionic environment. 23 Calix [4]pyrroles (C4P), in general, are a class of fluxional tetrapyrrolic macrocycles that bind selected anionic guests in organic solvents. 4c,24 Upon anion complexation, a change in the conformation of the C4P macrocycle occurs, converting it from the so-called 1,3-alternate to the corresponding cone conformation.…”

The Chemical Problem of Energy Change: Multi-Electron Processes

“…Such reactions have subsequently been termed metal-ioncoupled (or -ion-mediated) electron transfer. [49,50] The electron transfer rates from the donor are accelerated due to complexation of a redox-inactive metal with the radical anion of the substrate, significantly reducing the redox potential of the latter.…”