Issue 8, 2014

Long-range proton-coupled electron transfer in phenol–Ru(2,2′-bipyrazine)32+ dyads

Abstract

Two dyads in which either 4-cyanophenol or un-substituted phenol is connected via a p-xylene spacer to a Ru(bpz)32+ (bpz = 2,2′-bipyrazine) complex were synthesized and investigated. Selective photo-excitation of Ru(bpz)32+ at 532 nm in a CH3CN–H2O mixture leads to the formation of 4-cyanophenolate or phenolate along with Ru(bpz)32+ in its electronic ground state. This apparent photoacid behavior can be understood on the basis of a reaction sequence comprised of an initial photoinduced proton-coupled electron transfer (PCET) during which 4-cyanophenol or phenol is oxidized and deprotonated, followed by a thermal electron transfer event in the course of which 4-cyanophenoxyl or phenoxyl is reduced by Ru(bpz)3+ to 4-cyanophenolate or phenolate. Conceptually, this reaction sequence is identical to a sequence of photoinduced charge-separation and thermal charge-recombination events as observed previously for many electron transfer dyads, with the important difference that the initial photoinduced electron transfer process is proton-coupled. The dyad containing 4-cyanophenol reacts via concerted-proton electron transfer (CPET) whereas the dyad containing un-substituted phenol appears to react predominantly via a stepwise PCET mechanism. Long-range PCET is a key reaction in photosystem II. Understanding the factors that govern the kinetics of long-range PCET is desirable in the broader context of light-to-energy conversion by means of proton–electron separation across natural or artificial membranes.

Graphical abstract: Long-range proton-coupled electron transfer in phenol–Ru(2,2′-bipyrazine)32+ dyads

Supplementary files

Article information

Article type
Paper
Submitted
02 Dec 2013
Accepted
19 Dec 2013
First published
13 Jan 2014
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2014,16, 3617-3622

Long-range proton-coupled electron transfer in phenol–Ru(2,2′-bipyrazine)32+ dyads

C. Bronner and O. S. Wenger, Phys. Chem. Chem. Phys., 2014, 16, 3617 DOI: 10.1039/C3CP55071K

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