Time‐Resolved Interception of Multiple‐Charge Accumulation in a Sensitizer–Acceptor Dyad

Abstract

Biomimetic models that contain elements of photosynthesis are fundamental in the development of synthetic systems that can use sunlight to produce fuel. The critical task consists of running several rounds of light-induced charge separation, which is required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur. Long-lived first charge-separated state and distinct electronic signatures for the sequential charge accumulated species are essential features to be able to track these events on a spectroscopic ground. Herein, we use a double-excitation nanosecond pump-pump-probe experiment to interrogate two successive rounds of photo-induced electron transfer on a molecular dyad containing a naphthalene diimide (NDI) linked to a [Ru(bpy) ] (bpy=bipyridine) chromophore by using a reversible electron donor. We report an unprecedented long-lived two-electron charge accumulation (t=200 μs).

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

“…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.…”

“…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...…”

“…Molecular charge-photoaccumulating systemsanswering to this topological requirement are however rather scarce in the literature. [42][43][44][45] In 2018, we reported am ononuclear ruthenium tris-diimine complex with an extended phenazine-based ligand [1](PF 6 ) 2 (Scheme 1) which falls into the second category of charge-accumulating PS. [50,51] The phenazine ligand features at etracyclic pyridoquinolinone subunit inspired by the quinone-based electron storage and relay systems involved in photosynthesis.…”

Proton-coupled multi-electron transfer and its relevance for artificial photosynthesis and photoredox catalysis

“…60 There are now a handful of cases in which chargeaccumulation in purely molecular systems has been achieved without sacrificial reagents. 20,[61][62][63] However, for these systems it was crucial to have multiple donors for the accumulation of electrons on a single acceptor, or conversely, to have multiple acceptors for the accumulation of holes on a single donor. [62][63][64][65][66][67] Fig.…”

A Charge‐Separated State that Lives for Almost a Second at a Conductive Metal Oxide Interface

“…A number of studies have put great effort to achieving long‐lived charge separation in homogeneous supramolecular structures and heterogenous sensitized semiconducting metal oxide thin films . Notable examples include a 200 μs long‐lived intramolecular charge‐separated state in a sensitizer‐acceptor dyad, and lifetimes that range from tens of microseconds to the millisecond timescales at semiconducting metal oxide interfaces containing sensitizer‐donor molecular assemblies ,,. While these and most previous examples utilized non‐aqueous solutions, a related assembly has only recently been reported in aqueous solution .…”