An “All‐Green” Catalytic Cycle of Aqueous Photoionization

Abstract

Hydrated electrons are highly aggressive species that can force chemical transformations of otherwise unreactive molecules such as the reductive detoxification of halogenated organic compounds. We present the first example of the sustainable production of hydrated electrons through a homogeneous catalytic cycle driven entirely by green light (532 nm, coinciding with the maximum of the terrestrial solar spectrum). The catalyst is a metal complex serving as a "container" for a radical anion. This active center is generated from a ligand through quenching by a sacrificial electron donor, is shielded by the complex such that it stores the energy of the photon for much longer than a free radical anion could, and is finally ionized by another photon to regenerate the ligand and recover the starting complex quantitatively. The sacrificial donor can be a bioavailable reagent such as ascorbic acid.

A Green‐LED Driven Source of Hydrated Electrons Characterized from Microseconds to Hours and Applied to Cross‐Couplings

“…We recently found as ustainable access to e aq C À with visible light by the two-photon ionization of [Ru(bpy) 3 ] 2 + as catalyst with ascorbateA sc 2À as sacrificial donor. [2] When we raised the Asc 2À concentration to af ew tens of mm,t his system afforded laboratory-scale concentrations of e aq C À with single flashes from ag reen solid-state laser. [3] When we additionally shieldedt he catalystw ith an anionic micelle (of sodium dodecyl sulfate, SDS), ag reen light-emitting diode (LED) sufficed for the same purpose.…”

Generating Hydrated Electrons for Chemical Syntheses by Using a Green Light‐Emitting Diode (LED)

“…Eventually,t he second green photon adds its energy, with the total sufficing to eject e À aq from the excited *OER and thereby recover GS. [25] In effect, the gross reaction is thus at wo-photon ionization of Asc 2À such that this sacrificial donor may be regarded as a" caged" electron. The single parasitic reaction that empties the store is the bimolecular recombination between OER and the quenching by-product AscC À (rate constant, k rec ).…”

Time‐Resolved Chemically Induced Dynamic Nuclear Polarization of Biologically Important Molecules

“…Finally, in this section we would like to stress that geminate CIDNP is formed on the sub-ns timescale, subsequently, polarization evolves on the ms timescale due to F-pair reactions and the resulting polarization is preserved in the reaction product for the time periods given by the T 1 -relaxation times in diamagnetic products, which are typically about a few seconds for protons in small molecules. Hence, CIDNP contains information about fast processes involving radical intermediates; this information is stored for extended periods of time, allowing one to state that CIDNP is a "frozen signature" [35] of elusive radicals. Such radicals are often beyond the reach of conventional EPR methods (because of their short lifetimes and low stationary concentration) and optical methods (as they often do not have characteristic absorption bands) but can be detected by CIDNP in room-temperature solutions.…”