Exceptionally Long‐Lived Photodriven Multi‐Electron Storage without Sacrificial Reagents

Abstract

Photo-excitation of a molecular pentad in presence of Sc 3+ in de-aerated CH 3 CN leads to a quinone dianion that is stable on the millisecond timescale. Light-driven electron accumulation on the quinone unit is sensitized by two Ru(bpy) 3 2+ complexes in an intramolecular process, which relies on covalently attached triarylamine donors rather than on sacrificial reagents. Lewis acidLewis base interactions between Sc 3+ and quinone dianion are responsible for the exceptionally long lifetime of this photoproduct. Our study of photo-induced multi-electron transfer is relevant in the greater context of solar energy conversion.

Photo-triggered hydrogen atom transfer from an iridium hydride complex to unactivated olefins

“…23 Similarly, the interaction of Lewis acids with polar functional groups can help activate substrates that would be difficult to engage in pure PET chemistry. [24][25][26][27] We hypothesized that the photochemical hydrogenation of olens would be an ideal test ground for exploring the photo-HAT reactivity of a metal complex. Whilst alkene hydrogenation is of course an extremely well-developed eld, photochemical methods are very scarce and largely limited to substrates with strongly electron-withdrawing substituents to permit typical PET chemistry, 28 or to the reduction with solvated electrons.…”

Tuning the Electron Storage Potential of a Charge‐Photoaccumulating RuII Complex by a DFT‐Guided Approach

“…Ta king inspiration from these systems, more sophisticated light-harvesting units, capable of storing multiple electrons upon visible light irradiation,h ave been synthesized and studied. [20][21][22] Twoc onceptually differentm olecular designs have proven successful in storing multiple reducing equivalents in artificial photosynthetics ystems: either the system assembles multiple chromophores each of whichi ndependently transfers electrons to the acceptors ite (such as ab ridging ligand betweent wo chromophore units), [24][25][26][27][28][29][30][31][32][33][34][35][36][37] or it containsasingle protonated species [1H 2 ] 2 + .T he occurrence of PCET processes strongly lowers the reducing power of the system, precluding the use of charge photoaccumulation in [1H 2 ] 2 + to drive catalytic H 2 production.T his motivated us to search for structurally modified derivatives to store electrons at more negative potentials,e ven after protonation.U sing density functional theory( DFT) calculations, we screened electron-rich substituents ands elected the introduction of an oxime group in place of the carbonyl moiety in [1](PF 6 ) 2 .H erein we describe the process of this DFT-guidedd esign and the synthesis of the selected oxime-modified PS [2](PF 6 ) 2, together with its spectroscopic and (spectro)electrochemical characterization. Under irradiation in the presence of ap roton source, [2] 2 + transforms into the doubly protonated species [2H 2 ] 2 + ,w hichi sastronger reductant than [1H 2 ] 2 + .…”

“…Taking inspiration from these systems, more sophisticated light‐harvesting units, capable of storing multiple electrons upon visible light irradiation, have been synthesized and studied . Two conceptually different molecular designs have proven successful in storing multiple reducing equivalents in artificial photosynthetic systems: either the system assembles multiple chromophores each of which independently transfers electrons to the acceptor site (such as a bridging ligand between two chromophore units), or it contains a single chromophore and relies on a sacrificial electron donor to perform multiple excitation–accumulation cycles . In the latter case, either a single or multiple electron storage sites can be assembled adjacent to the chromophore.…”

“…In the latter case, either a single or multiple electron storage sites can be assembled adjacent to the chromophore. Typical light‐harvesting units are porphyrins, Ir III[37] or Ru II polypyridine complexes, covalently linked to a wide variety of electron storage sites, such as a metal centre, polyoxometalates, naphthalene diimide, perylene diimide, anthraquinone, or π‐extended phenanthroline‐based ligands. Recently, Wenger and co‐workers produced one of the first examples of the beneficial role played by electron photoaccumulation in photoredox catalysis.…”

“…Moreover,t he ability of this novel artificial photosynthetic system to store two photogenerated electrons at a more reducing potential, via ap roton-coupled electrontransfer mechanism,was demonstrated.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.chromophore and relies on as acrificiale lectron donor to perform multiple excitation-accumulation cycles. [38][39][40][41][42][43][44][45] In the latter case, either as ingle or multiple electron storage sites can be assembled adjacentt ot he chromophore.T ypical light-harvesting units are porphyrins, [24,36] Ir III[37] or Ru II polypyridine [25][26][27][28][29][30][31][32][33][34][35][38][39][40][41][42][43][44][45] complexes,c ovalently linked to aw ide variety of electron storage sites, such as am etal centre, [25] polyoxometalates, [13,36] naphthalene diimide, [35,45] perylene diimide, [24] anthraquinone, [30,33,34] or p-extended phenanthroline-based [26-29, 44, 46, 47] ligands.R ecently,W enger and co-workers produced one of the first examples of the beneficial role played by electron photoaccumulation in photoredox catalysis. They used assemblies of Ru II chromophores with ac entral dibenzo[1,2]dithiin electron storageu nit to accumulate two photogenerated electrons, further used to perform dithiolate/disulfide int...…”