Photoexcited radical anion super-reductants for solar fuels catalysis

Iron(III) Carbene Complexes with Tunable Excited State Energies for Photoredox and Upconversion

Substituting precious elements in luminophores and photocatalysts by abundant first-row transition metals remains a significant challenge, and iron continues to be particularly attractive owing to its high natural abundance and low cost. Most iron complexes known to date face severe limitations due to undesirably efficient deactivation of luminescent and photoredox-active excited states. Two new iron(III) complexes with structurally simple chelate ligands enable straightforward tuning of ground and excited state properties, contrasting recent examples, in which chemical modification had a minor impact. Crude samples feature two luminescence bands strongly reminiscent of a recent iron(III) complex, in which this observation was attributed to dual luminescence, but in our case, there is clear-cut evidence that the higher-energy luminescence stems from an impurity and only the red photoluminescence from a doublet ligand-to-metal charge transfer (2LMCT) excited state is genuine. Photoinduced oxidative and reductive electron transfer reactions with methyl viologen and 10-methylphenothiazine occur with nearly diffusion-limited kinetics. Photocatalytic reactions not previously reported for this compound class, in particular the C-H arylation of diazonium salts and the aerobic hydroxylation of boronic acids, were achieved with low-energy red light excitation. Doublet-triplet energy transfer (DTET) from the luminescent 2LMCT state to an anthracene annihilator permits the proof of principle for triplet-triplet annihilation upconversion based on a molecular iron photosensitizer. These findings are relevant for the development of iron complexes featuring photophysical and photochemical properties competitive with noble-metal-based compounds.

Spatial Distributions of Single-Molecule Reactivity in Plasmonic Catalysis

Plasmonic catalysts have the potential to accelerate and control chemical reactions with light by exploiting localized surface plasmon resonances. However, the mechanisms governing plasmonic catalysis are not simple to decouple. Several plasmon-derived phenomena, such as electromagnetic field enhancements, temperature, or the generation of charge carriers, can affect the reactivity of the system. These effects are convoluted with the inherent (nonplasmonic) catalytic properties of the metal surface. Disentangling these coexisting effects is challenging but is the key to rationally controlling reaction pathways and enhancing reaction rates. This study utilizes super-resolution fluorescence microscopy to examine the mechanisms of plasmonic catalysis at the single-particle level. The reduction reaction of resazurin to resorufin in the presence of Au nanorods coated with a porous silica shell is investigated in situ. This allows the determination of reaction rates with a single-molecule sensitivity and subparticle resolution. By variation of the irradiation wavelength, it is possible to examine two different regimes: photoexcitation of the reactant molecules and photoexcitation of the nanoparticle's plasmon resonance. In addition, the measured spatial distribution of reactivity allows differentiation between superficial and far-field effects. Our results indicate that the reduction of resazurin can occur through more than one reaction pathway, being most efficient when the reactant is photoexcited and is in contact with the Au surface. In addition, it was found that the spatial distribution of enhancements varies, depending on the underlying mechanism. These findings contribute to the fundamental understanding of plasmonic catalysis and the rational design of future plasmonic nanocatalysts.

Probing the influence of substrate binding on photocatalytic dehalogenation with a heteroleptic supramolecular [M4La2Lb2] square containing PDI photosensitizers as ligands

Photoredox catalysis is a valuable tool in a large variety of chemical reactions. Main challenges still to be overcome are photodegradation of photocatalysts and substrates, short lifetimes of reactive intermediates, and selectivity issues due to unwanted side reactions. A potential solution to these challenges is the pre-organization of the photosensitizer, substrate and (co)-catalyst in supramolecular self-assembled structures. In such architectures, (organic) dyes can be stabilized, and higher selectivity could potentially be achieved through pre-organizing desired reaction partners via non-covalent interactions. Perylene diimide (PDI) is an organic dye, which can be readily reduced to its mono- and dianion. Excitation of both anions leads to highly reducing excited states, which are able to reduce a variety of substrates via single electron transfer. The incorporation of PDI into a heteroleptic [M4La2Lb2] supramolecular square has been recently demonstrated. Herein we investigate its photophysical properties and demonstrate that incorporated PDI indeed features photocatalytic activity. Initial results suggest that the pre-organisation by binding positively affects the outcome.

Chalcogen-bridged coordination polymer for the photocatalytic activation of aryl halides

The ability to deliver electrons is vital for dye-based photocatalysts. Conventionally, the aromatic stacking-based charge-transfer complex increases photogenerated electron accessibility but decreases the energy of excited-state dyes. To circumvent this dilemma, here we show a strategy by tuning the stacking mode of dyes. By decorating naphthalene diimide with S-bearing branches, the S···S contact-linked naphthalene diimide string is created in coordination polymer, thereby enhancing electron mobility while simultaneously preserving competent excited-state reducing power. This benefit, along with in situ assembly between naphthalene diimide strings and exogenous reagent/reactant, improves the accessibility of short-lived excited states during consecutive photon excitation, resulting in greater efficiency in photoinduced electron-transfer activation of inert bonds in comparison to other coordination polymers with different dye-stacking modes. This heterogeneous approach is successfully applied in the photoreduction of inert aryl halides and the successive formation of C_Ar-C/S/P/B bonds with potential pharmaceutical applications.

Spectroscopy and Theoretical Modeling of Tetracene Anion Resonances

The positions and widths of the optically allowed electronic states of the tetracene radical anion located above the detachment threshold energy (i.e anion resonances) are mapped out using total photodetachment yield spectroscopy of cryogenically cooled ions. The presence of these states is detected via the sharp increase in the photodetachment yield compared to that of the monotonic nonresonant direct photodetachment background. The resolution of the resulting spectrum is limited by the ∼5 cm^-1 line width of the tunable laser and thus provides a stringent benchmark for computations of the energies and autodetachment lifetimes of these resonance states. The experimental results are compared to high-level electronic structure computations and line width modeling using the orbital stabilization method. These theoretical results are found to be in near quantitative agreement with the experimental data, highlighting their capability to accurately describe the energies and lifetimes of anion resonances for relatively large molecules.

Intermediate Complex-Mediated Interfacial Electron Transfer in a Radical Dianion/TiO2 Dye-Sensitized Photocatalytic System

We present a mechanistic study of a PTCDA^2-/TiO₂ dye-sensitized photocatalytic system, in which the stable radical dianion PTCDA^2- is formed via a two-step consecutive photoinduced electron transfer from its neutral precursor PTCDA (i.e., perylenetetracarboxylic dianhydride). Photoexcitation of PTCDA^2- brings forth an interesting behavior known as vibrationally excited-state-selective, visible-light photocatalytic hydrogen evolution reaction (HER). In conjunction with the information gleaned from optical spectroscopy and ultrafast dynamics, we reveal that an intermediate complex (IC) state with a lifetime of ∼12 ps exists in the vicinity of a certain vibrationally excited state of PTCDA^2-. Such a unique IC state mediates the interfacial electron transfer (IET) channel from the specific excited state of PTCDA^2- to the conduction band continuum of TiO₂. As an outcome, the effective IC-mediated IET process in this photocatalytic system leads to a remarkable HER rate that reaches ∼4660 μmol g^-1 h^-1.

Red Light-Based Dual Photoredox Strategy Resembling the Z-Scheme of Natural Photosynthesis

Photoredox catalysis typically relies on the use of single chromophores, whereas strategies, in which two different light absorbers are combined, are rare. In photosystems I and II of green plants, the two separate chromophores P₆₈₀ and P₇₀₀ both absorb light independently of one another, and then their excitation energy is combined in the so-called Z-scheme, to drive an overall reaction that is thermodynamically very demanding. Here, we adapt this concept to perform photoredox reactions on organic substrates with the combined energy input of two red photons instead of blue or UV light. Specifically, a Cu^I bis(α-diimine) complex in combination with in situ formed 9,10-dicyanoanthracenyl radical anion in the presence of excess diisopropylethylamine catalyzes ca. 50 dehalogenation and detosylation reactions. This dual photoredox approach seems useful because red light is less damaging and has a greater penetration depth than blue or UV radiation. UV-vis transient absorption spectroscopy reveals that the subtle change in solvent from acetonitrile to acetone induces a changeover in the reaction mechanism, involving either a dominant photoinduced electron transfer or a dominant triplet-triplet energy transfer pathway. Our study illustrates the mechanistic complexity in systems operating under multiphotonic excitation conditions, and it provides insights into how the competition between desirable and unwanted reaction steps can become more controllable.

Ultrafast photooxidation of protein-bound anionic flavin radicals

Flavoproteins are colored proteins involved in a large variety of biochemical reactions. They can perform photochemical reactions, which are increasingly exploited for bioengineering new protein-derived photocatalysts. In particular, light-induced reduction of the resting oxidized state of the flavin by close-lying amino acids or substrates is extensively studied. Here, we demonstrate that the reverse and previously unknown reaction photooxidation of the anionic semireduced flavin radical, a short-lived reaction intermediate in many biochemical reactions, efficiently occurs in flavoprotein oxidases. We anticipate that this finding will allow photoreduction of external reactants and lead to exploration of novel photocatalytic pathways.

The photophysical properties of anionic semireduced flavin radicals are largely unknown despite their importance in numerous biochemical reactions. Here, we studied the photoproducts of these intrinsically unstable species in five different flavoprotein oxidases where they can be stabilized, including the well-characterized glucose oxidase. Using ultrafast absorption and fluorescence spectroscopy, we unexpectedly found that photoexcitation systematically results in the oxidation of protein-bound anionic flavin radicals on a time scale of less than ∼100 fs. The thus generated photoproducts decay back in the remarkably narrow 10- to 20-ps time range. Based on molecular dynamics and quantum mechanics computations, positively charged active-site histidine and arginine residues are proposed to be the electron acceptor candidates. Altogether, we established that, in addition to the commonly known and extensively studied photoreduction of oxidized flavins in flavoproteins, the reverse process (i.e., the photooxidation of anionic flavin radicals) can also occur. We propose that this process may constitute an excited-state deactivation pathway for protein-bound anionic flavin radicals in general. This hitherto undocumented photochemical reaction in flavoproteins further extends the family of flavin photocycles.

Radical Anions and Dianions of Naphthalenediimides Generated within Layer-by-Layer Zirconium Phosphonate Thin Films

Chemical reduction of N,N'-bis(2-phosphonoethyl)-1,4,5,8-naphthalenediimide (PNDI) with the reducing agent sodium dithionite gave stable colored reduced species, both in homogeneous solutions and in self-assembled thin films. When colorless PNDI aqueous solutions were titrated with the reducing agent, stepwise reduction was observed, giving first the radical anion (PNDI^-•) and then the dianion (PNDI^2-) species, which were detected by UV-visible-NIR spectroscopy, allowing the unambiguous determination of absorption maxima and molar absorptivities for each species. The radical anion PNDI^-• was found to form π-dimers in water, but monomeric PNDI^-• was formed in the presence of the cationic surfactant cetyltrimethylammonium bromide, indicating association with the micelles. Thin films of PNDI with 25 layers were grown by the zirconium phosphonate method on quartz substrates. Reduction of the films with sodium dithionite also produced radical anions and dianions of PNDI. However, reduction in the films was much slower than in solution, evidencing the compactness of the films. Moreover, reduction in the films did not proceed to completion, even with excess of the reducing agent, which can be attributed to the repulsion of negative charges within the film.

Ultrastable radicals in naphthalenediimide-based materials and their stimulus-boosting near-infrared photothermal conversion

Ultrastable radicals in NDI-based crystals are formed by intrinsic electron transfer. Extra light or heat can effectively promote electron transfer, leading to more air-, light- and heat-stable radicals with efficient NIR photothermal conversion.

Photochromic Polyoxometalate/Perylenediimide Donor-Acceptor Hybrid Crystals with Interesting Luminescent Properties

The self-assembly of electron-deficient protonated N, N'-dipyridyltetrachloroperylenediimide (4Cl-DPPDI) and electron-rich polyoxometalate acids H_nXM₁₂O₄₀ (POMs; X = P or Si; M = W or Mo) resulted in four isomorphous donor-acceptor hybrid crystals 1-4 with segregated POM anions and one-dimensional racemic hydrogen-bonded 4Cl-DPPDI networks as electron-donor and -acceptor components, respectively. Because of the compact contacts between the POM anions and 4Cl-DPPDI tectons induced by anion-π interactions, besides enhanced photochromism, these four unique isostructural hybrids exhibited unusual room-temperature phosphorescence (RTP) emissions. More interestingly, owing to the facial compact contacts of two racemic 4Cl-DPPDI tectons induced by lone pair-π-assisted π-π interactions, they also showed unprecedented photon upconversion by triplet-triplet annihilation (TTA).

Photophysics of Perylene Diimide Dianions and Their Application in Photoredox Catalysis

The two‐electron reduced forms of perylene diimides (PDIs) are luminescent closed‐shell species whose photochemical properties seem underexplored. Our proof‐of‐concept study demonstrates that straightforward (single) excitation of PDI dianions with green photons provides an excited state that is similarly or more reducing than the much shorter‐lived excited states of PDI radical monoanions, which are typically accessible after biphotonic excitation with blue photons. Thermodynamically demanding photocatalytic reductive dehalogenations and reductive C−O bond cleavage reactions of lignin model compounds have been performed using sodium dithionite acts as a reductant, either in aqueous solution or in biphasic water–acetonitrile mixtures in the presence of a phase transfer reagent. Our work illustrates the concept of multi‐electron reduction of a photocatalyst by a sacrificial reagent prior to irradiation with low‐energy photons as a means of generating very reactive excited states.

Prediction of the standard potentials for one-electron oxidation of N,N,N',N' tetrasubstituted p-phenylenediamines by calculation

The formal potentials for the reversible one-electron oxidation of N,N,N',N' tetrasubstituted p-phenylenediamines in acetonitrile have been applied as a test set for benchmarking computational methods for a series of compounds with only small structural differences. The aim of the study is to propose a simple method for calculating the standard oxidation potentials, and therefore, the protocol is progressively developed by adding more terms in the energy expression. In addition, the effect of including implicit solvation models (IEFPCM, CPCM, and SMD), larger basis sets, and correlation methods are investigated. The oxidation potentials calculated using the G3MP2B3 approach with IEFPCM resulted in the best fit (R² = 0.9624), but the slope of the correlation line, 0.74, is far from the optimal value, 1.00. B3LYP/6-311++G(d,p) and TPSSh/6-311++G(2d,p) yielded only slightly less consistent data (R² = 0.9388 and R² = 0.9425), but with much better slopes, 1.00 and 0.94, respectively. We conclude that it is important to investigate the basis set size and treatment of electron correlation when calculating oxidation potentials for N,N,N',N' tetrasubstituted p-phenylenediamines.

Electrochemical Activation of Diverse Conventional Photoredox Catalysts Induces Potent Photoreductant Activity*

Herein, we disclose that electrochemical stimulation induces new photocatalytic activity from a range of structurally diverse conventional photocatalysts. These studies uncover a new electron-primed photoredox catalyst capable of promoting the reductive cleavage of strong C(sp2 )-N and C(sp2 )-O bonds. We illustrate several examples of the synthetic utility of these deeply reducing but otherwise safe and mild catalytic conditions. Finally, we employ electrochemical current measurements to perform a reaction progress kinetic analysis. This technique reveals that the improved activity of this new system is a consequence of an enhanced catalyst stability profile.

Sensitization-initiated electron transfer via upconversion: mechanism and photocatalytic applications

Sensitization-initiated electron transfer (SenI-ET) describes a recently discovered photoredox strategy that relies on two consecutive light absorption events, triggering a sequence of energy and electron transfer steps. The cumulative energy input from two visible photons gives access to thermodynamically demanding reactions, which would be unattainable by single excitation with visible light. For this reason, SenI-ET has become a very useful strategy in synthetic photochemistry, but the mechanism has been difficult to clarify due to its complexity. We demonstrate that SenI-ET can operate via sensitized triplet-triplet annihilation upconversion, and we provide the first direct spectroscopic evidence for the catalytically active species. In our system comprised of fac-[Ir(ppy)₃] as a light absorber, 2,7-di-tert-butylpyrene as an annihilator, and N,N-dimethylaniline as a sacrificial reductant, all photochemical reaction steps proceed with remarkable rates and efficiencies, and this system is furthermore suitable for photocatalytic aryl dehalogenations, pinacol couplings and detosylation reactions. The insights presented here are relevant for the further rational development of photoredox processes based on multi-photon excitation, and they could have important implications in the greater contexts of synthetic photochemistry and solar energy conversion.

Naphthalene diimides: perspectives and promise

In this review, we describe the developments in the field of naphthalene diimides (NDIs) from 2016 to the presentday. NDIs are shown to be an increasingly interesting class of molecules due to their electronic properties, large electron deficient aromatic cores and tendency to self-assemble into functional structures. Almost all NDIs possess high electron affinity, good charge carrier mobility, and excellent thermal and oxidative stability, making them promising candidates for applications in organic electronics, photovoltaic devices, and flexible displays. NDIs have also been extensively studied due to their potential real-world uses across a wide variety of applications including supramolecular chemistry, sensing, host-guest complexes for molecular switching devices, such as catenanes and rotaxanes, ion-channels, catalysis, and medicine and as non-fullerene accepters in solar cells. In recent years, NDI research with respect to supramolecular assemblies and mechanoluminescent properties has also gained considerable traction. Thus, this review will assist a wide range of readers and researchers including chemists, physicists, biologists, medicinal chemists and materials scientists in understanding the scope for development and applicability of NDI dyes in their respective fields through a discussion of the main properties of NDI derivatives and of the status of emerging applications.

Aryl dechlorination and defluorination with an organic super-photoreductant

Direct excitation of the commercially available super-electron donor tetrakis(dimethylamino)ethylene (TDAE) with light-emitting diodes at 440 or 390 nm provides a stoichiometric reductant that is able to reduce aryl chlorides and fluorides. The method is very simple and requires only TDAE, substrate, and solvent at room temperature. The photoactive excited state of TDAE has a lifetime of 17.3 ns in cyclohexane at room temperature and an oxidation potential of ca.-3.4 V vs. SCE. This makes TDAE one of the strongest photoreductants able to operate on the basis of single excitation with visible photons. Direct substrate activation occurs in benzene, but acetone is reduced by photoexcited TDAE and substrate reduction takes place by a previously unexplored solvent radical anion mechanism. Our work shows that solvent can have a leveling effect on the photochemically available redox power, reminiscent of the pH-leveling effect that solvent has in acid-base chemistry.

Yield-not only Lifetime-of the Photoinduced Charge-Separated State in Iridium Complex-Polyoxometalate Dyads Impact Their Hydrogen Evolution Reactivity

Covalently linked photosensitizer-polyoxometalate (PS-POM) dyads are promising molecular systems for light-induced energy conversion processes, such as "solar" hydrogen generation. To date, very little is known of their fundamental photophysical properties which affect the catalytic reactivity and stability of the systems. PS-POM dyads often feature short-lived photoinduced charge-separated states, and the lifetimes of these states are considered crucial for the function of PS-POM dyads in molecular photocatalysis. Hence, strategies have been developed to extend the lifetimes of the photoinduced charge-separated states, either by tuning the PS photophysics or by tuning the POM redox properties. Recently, some of us reported PS-POM dyads based on cyclometalated Ir^III complexes covalently linked to Anderson-type polyoxometalate. Distinct hydrogen evolution reactivity (HER) of the dyads was observed, which was tuned by varying the central metal ion M of the POM_M (M=Mn³⁺ , Co³⁺ , Fe³⁺ ). In this manuscript, the photoinduced electron-transfer processes in the three Ir-POM_M dyads are investigated to rationalize the underlying reasons for the differences in HER activity observed. We report that upon excitation of the Ir^III complex, ultrafast (sub-ps) charge separation occurs, leading to different amounts of the charge-separated states (Ir^.+ -POM_M ^.- ) generated in the different dyads. However, in all dyads studied, the resulting Ir^.+ -POM_M ^.- species are short-lived (sub-ns) when compared to reference electron acceptors (e.g. porphyrins or fullerenes) reported in the literature. The reductive quenching of Ir^.+ -POM_M ^.- by a sacrificial donor, triethyl amine (1 m), to generate the intermediate Ir-POM_M ^.- is estimated to be very efficient (70-80 %) for all dyads studied. Based on this analyses, we conclude that the yield instead of the lifetime of the Ir^.+ -POM_M ^.- charge-separated state determines the catalytic capacity of the dyads investigated. This new feature in the PS-POM photophysics could lead to new design criteria for the development of novel PS-POM dyads.

Multi-Photon Excitation in Photoredox Catalysis: Concepts, Applications, Methods

The energy of visible photons and the accessible redox potentials of common photocatalysts set thermodynamic limits to photochemical reactions that can be driven by traditional visible-light irradiation. UV excitation can be damaging and induce side reactions, hence visible or even near-IR light is usually preferable. Thus, photochemistry currently faces two divergent challenges, namely the desire to perform ever more thermodynamically demanding reactions with increasingly lower photon energies. The pooling of two low-energy photons can address both challenges simultaneously, and whilst multi-photon spectroscopy is well established, synthetic photoredox chemistry has only recently started to exploit multi-photon processes on the preparative scale. Herein, we have a critical look at currently developed reactions and mechanistic concepts, discuss pertinent experimental methods, and provide an outlook into possible future developments of this rapidly emerging area.

Linear correlation models for the redox potential of organic molecules in aqueous solutions

In this study, we use the molecular orbital energy approximation (MOEA) and the energy difference approximation (EDA) to build linear correlation models for the redox potentials of 53 organic compounds in aqueous solutions. The molecules evaluated include nitroxides, phenols, and amines. Both the MOEA and EDA methods yield similar correlation models, however, the MOEA method is less computationally expensive. Correlation coefficients (R²) below 0.3 and mean absolute errors above 0.25 V were found for correlation models built without solvent effects. When explicit water molecules and a continuum solvent model are added to the calculations, correlation coefficients close to 0.8 are reached, and mean absolute errors below 0.18 V are obtained. The incorporation of solvent effects is necessary for good correlation models, particularly for redox processes of charged molecules in aqueous solutions. A comparison of the correlation models from different methodologies is provided. Graphical abstract.

Potent Reductants via Electron-Primed Photoredox Catalysis: Unlocking Aryl Chlorides for Radical Coupling

We describe a new catalytic strategy to transcend the energetic limitations of visible light by electrochemically priming a photocatalyst prior to excitation. This new catalytic system is able to productively engage aryl chlorides with reduction potentials hundreds of millivolts beyond the potential of Na0 in productive radical coupling reactions. The aryl radicals produced via this strategy can be leveraged for both carbon-carbon and carbon-heteroatom bond-forming reactions. Through direct comparison, we illustrate the reactivity and selectivity advantages of this approach relative to electrolysis and photoredox catalysis.

Doubly zwitterionic, di-reduced, highly electron-rich, air-stable naphthalenediimides: redox-switchable islands of aromatic-antiaromatic states

The di-reduced state of the naphthalene moiety and its congeners have long captivated chemists as it is elusive to stabilize these intrinsically reactive electron-rich π-systems and for their emergent multifaceted properties. Herein we report the synthesis and isolation of two-electron (2e^-) reduced, highly electron-rich naphthalenediimides (NDIs). A doubly zwitterionic structure is observed for the first time in a naphthalene moiety and validated by single crystal X-ray crystallography and spectroscopic methods. The synthesis avoids hazardous reducing agents and offers an easy, high-yielding route to bench-stable di-reduced NDIs. Notably, we realized high negative first oxidation potentials of up to -0.730 V vs. Fc/Fc⁺ in these systems, which establish these systems to be one of the strongest ambient stable electron donors. The study also provides the first insights into the NMR spectra of the di-reduced systems revealing a large decrease in diatropicity of the naphthalene ring compared to its 2e^- oxidized form. The NICS, NICS-XY global ring current, gauge-including magnetically induced current (GIMIC) and AICD ring current density calculations revealed switching of the antiaromatic and aromatic states at the naphthalene and the imide rings, respectively, in the di-reduced system compared to the 2e^- oxidized form. Notably, the substituents at the phosphonium groups significantly tune the antiaromatic-aromatic states and donor ability, and bestow an array of colors to the di-reduced systems by virtue of intramolecular through-space communication with the NDI scaffold. Computational studies showed intramolecular noncovalent interactions to provide additional stability to these unprecedented doubly zwitterionic systems.

Visible-Light-Triggered Generation of Ultrastable Radical Anion from Nitro-substituted Perylenediimides

An efficient method for visible-light-triggered generation of radicals from mono- and dinitro-substituted perylenediimide derivatives is developed. UV-vis-NIR and electron paramagnetic resonance measurements were carried out to confirm the formation of radicals. Most importantly, these radical anions were remarkably stable for several months. Subsequently, the reversible nature of anions was validated by both chemical and spectroelectrochemical methods for applications in electrochromic materials.

Photoexcited perylene diimide radical anions for the reduction of aryl halides: a bay-substituent effect

Photoexcited perylene diimide radical anions exhibit remarkable substituent-dependent photocatalytic activities towards the reduction of aryl halides, which are mainly controlled by their excited-state reduction potentials and SOMO−1 energies.

Photocatalytic H2production by dirhodium(ii,ii) photosensitizers with red light

Photocatalytic H₂evolution uponλ_irr= 655 nm with dirhodium(ii,ii) photosensitizers demonstrates tunable oxidative and reductive quenching mechanisms.