Chemically Mediated Artificial Electron Transport Chain

Abstract

Electron transport chains (ETCs) are ubiquitous in nearly all living systems. Replicating the complexity and control inherent in these multicomponent systems using ensembles of small molecules opens up promising avenues for molecular therapeutics, catalyst design, and the development of innovative energy conversion and storage systems. Here, we present a noncovalent, multistep artificial electron transport chains comprising cyclo[8]pyrrole (1), a meso-aryl hexaphyrin(1.0.1.0.1.0) (naphthorosarin 2), and the small molecules I₂ and trifluoroacetic acid (TFA). Specifically, we show that 1) electron transfer occurs from 1 to give I₃^– upon the addition of I₂, 2) proton-coupled electron transfer (PCET) from 1 to give H₃2^•2+ and H₃2⁺ upon the addition of TFA to a dichloromethane mixture of 1 and 2, and 3) that further, stepwise treatment of 1 and 2 with I₂ and TFA promotes electron transport from 1 to give first I₃^– and then H₃2^•2+ and H₃2⁺. The present findings are substantiated through UV-vis-NIR, ¹H NMR, electron paramagnetic resonance (EPR) spectroscopic analyses, cyclic voltammetry studies, and DFT calculations. Single-crystal structure analyses were used to characterize compounds in varying redox states.

Presented is an example of a proton-coupled electron transfer (PCET) system comprising an artificial electron transport chain (ETC) that can be regulated by small molecules or concentration control.