Combining energy and electron transfer in a supramolecular environment for the "green" generation and utilization of hydrated electrons through photoredox catalysis. Issue 6 (7th March 2016)

• Record Type: Journal Article
• Authors: Kerzig, Christoph; Goez, Martin
• Is Part Of: Chemical science. Volume 7:Issue 6(2016:Jun.)
• Page Start: 3862
• Page End: 3868
• Publication Date: 2016-03-07
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c5sc04800a
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : The interaction of an anionic micelle with the molecular charges and dipole moments ensures the desired sequence of processes and suppresses cross reactions in an "all-green" photoredox catalytic access to hydrated electronse˙−aq, which reductively decompose nonactivated chloro-organics. Abstract : We present a new mechanism that sustainably produces hydrated electrons, i.e., extremely strong reductants, yet consumes only green photons (532 nm) and the bioavailable ascorbate as sacrificial donor. The mechanism couples an energy-transfer cycle, in which a light-harvesting ruthenium polypyridine complex absorbs a first photon and passes the excitation energy on to a pyrene-based redox catalyst, with an electron-transfer cycle, in which the resulting triplet is reductively quenched and the energy-rich aryl radical anion is finally ionized by a second photon. Thus separating the roles of primary and secondary absorber permitted choosing a redox catalyst with a nonabsorbing ground state but efficiently ionizable radical anion; the quantum yield of the ionization step in our complex mechanism surpasses that in a simple photoredox cycle featuring only the metal complex by a factor of four. We suppressed undesired cross reactions through the noncovalent interactions of an anionic micelle with the charges of the reactants, intermediates, and products: the cationic light-harvesting complex remains affixed to the micelle surface, which blocks the access of the negatively charged sacrificial donor, aryl radical anion and hydrated electron, but allows the pyrene ground-state almost unhindered entry into the Stern layer despite a carboxylate substituent by virtue of its large dipole moment. We demonstrate the applicability of the mechanism to the reductive detoxification of halogenated organic waste, which hitherto required UV-C for electron generation, by decomposing the typical model compound chloroacetate.