Extended charge accumulation in ruthenium–4H-imidazole-based black absorbers: a theoretical design concept

Abstract

A theoretical-guided design concept aiming to achieve highly efficient unidirectional charge transfer and multi-charge separation upon successive photoexcitation for light-harvesting dyes in the scope of supramolecular photocatalysts is presented. Four 4H-imidazole-ruthenium(ii) complexes incorporating a biimidazole-based electron-donating ligand sphere have been designed based on the well-known 4H-imidazole-ruthenium(ii) polypyridyl dyes. The quantum chemical evaluation, performed at the density functional and time-dependent density functional level of theory, revealed extraordinary unidirectional charge transfer bands from the near-infrared to the ultraviolet region of the absorption spectrum upon multi-photoexcitation. Spectro-electrochemical simulations modeling photoexcited intermediates determined the outstanding multi-electron storage capacity for this novel class of black dyes. These remarkable photochemical and photophysical properties are found to be preserved upon site-specific protonation rendering 4H-imidazole-ruthenium(ii) biimidazole dyes ideal for light-harvesting applications in the field of solar energy conversion.

An artificial photosynthetic system for photoaccumulation of two electrons on a fused dipyridophenazine (dppz)–pyridoquinolinone ligand

“… 33 This precludes the use of previously reported systems in which two photosensitizing units straddle the accumulation site. 14 , 18 , 19 , 24 , 29 , 30 , 32 Conversely, systems based on a single light-harvesting center such as iminoimidazole-containing ruthenium photosensitizers, whose properties have been studied by two of us, 34 , 35 and disubstituted dipyrido-[3,2- a :2′,3′- c ]phenazine (dppz)-based ruthenium complexes 36 are instrumental to the aim of designing molecular photoelectrodes with enhanced efficiency. We therefore designed a novel ruthenium tris-diimine complex, [1](PF 6 ) 2 ( Scheme 1 ), that features an original bent-shaped polyazaaromatic ligand, namely a pyridoquinolinone moiety fused to a dppz-chelating unit.…”

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.…”

“…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...…”

“…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.…”