Reversible Electron Transfer Research Articles

Designed Long‐Lived Emission from CdSe Quantum Dots through Reversible Electronic Energy Transfer with a Surface‐Bound Chromophore

AbstractThe size‐tunable emission of luminescent quantum dots (QDs) makes them highly interesting for applications that range from bioimaging to optoelectronics. For the same applications, engineering their luminescence lifetime, in particular, making it longer, would be as important; however, no rational approach to reach this goal is available to date. We describe a strategy to prolong the emission lifetime of QDs through electronic energy shuttling to the triplet excited state of a surface‐bound molecular chromophore. To implement this idea, we made CdSe QDs of different sizes and carried out self‐assembly with a pyrene derivative. We observed that the conjugates exhibit delayed luminescence, with emission decays that are prolonged by more than 3 orders of magnitude (lifetimes up to 330 μs) compared to the parent CdSe QDs. The mechanism invokes unprecedented reversible quantum dot to organic chromophore electronic energy transfer.

One-megadalton metalloenzyme complex in Geobacter metallireducens involved in benzene ring reduction beyond the biological redox window

Reversible biological electron transfer usually occurs between redox couples at standard redox potentials ranging from +0.8 to -0.5 V. Dearomatizing benzoyl-CoA reductases (BCRs), key enzymes of the globally relevant microbial degradation of aromatic compounds at anoxic sites, catalyze a biological Birch reduction beyond the negative limit of this redox window. The structurally characterized BamBC subunits of class II BCRs accomplish benzene ring reduction at an active-site tungsten cofactor; however, the mechanism and components involved in the energetic coupling of endergonic benzene ring reduction have remained hypothetical. We present a 1-MDa, membrane-associated, Bam[(BC)2DEFGHI]2 complex from the anaerobic bacterium Geobacter metallireducens harboring 4 tungsten, 4 zinc, 2 selenocysteines, 6 FAD, and >50 FeS cofactors. The results suggest that class II BCRs catalyze electron transfer to the aromatic ring, yielding a cyclic 1,5-dienoyl-CoA via two flavin-based electron bifurcation events. This work expands our knowledge of energetic couplings in biology by high-molecular-mass electron bifurcating machineries.

Voltammetric Study of Antitumor Efficient Ethylenediamine-Type of Ligands

The electrochemical behavior of four dialkyl esters (methyl, ethyl, n-propyl and n-butyl) of (S,S)-α,α′-(1,2-ethanediyldiimino)-bis[cyclohexanepropanoic acid] with moderate antitumor activity has been studied by cyclic voltammetry. I-E curves recorded at boron-doped diamond electrode in −2.00 < Ep < 0.00 V range show a single oxidative peak located in the −0.95 < Ep,a < −0.52 V region in a form of one-electron wave. The electrochemical processes appear to be irreversible for all compounds except for the compound with methyl substituent which demonstrates well-defined reversible electron transfer. Derivatives with bulkier moieties are easier to oxidize. For all investigated compounds an amine-centered redox process is dominant. Further investigation indicates that electrochemical reaction is diffusion controlled, chemically irreversible process. The results are discussed in terms of linking their electrochemical activity to antitumor effect.

Angiotensin receptor blockade improves cardiac mitochondrial activity in response to an acute glucose load in obese insulin resistant rats

Hyperglycemia increases the risk of oxidant overproduction in the heart through activation of a multitude of pathways. Oxidation of mitochondrial enzymes may impair their function resulting in accumulation of intermediates and reverse electron transfer, contributing to mitochondrial dysfunction. Furthermore, the renin-angiotensin system (RAS) becomes inappropriately activated during metabolic syndrome, increasing oxidant production. To combat excess oxidant production, the transcription factor, nuclear factor erythriod-2- related factor 2 (Nrf2), induces expression of many antioxidant genes. We hypothesized that angiotensin II receptor type 1 (AT1) blockade improves mitochondrial function in response to an acute glucose load via upregulation of Nrf2. To address this hypothesis, an oral glucose challenge was performed in three groups prior to dissection (n = 5–8 animals/group/time point) of adult male rats: 1) Long Evans Tokushima Otsuka (LETO; lean strain-control), 2) insulin resistant, obese Otsuka Long Evans Tokushima Fatty (OLETF), and 3) OLETF + angiotensin receptor blocker (ARB; 10mg olmesartan/kg/d × 6 weeks). Hearts were collected at T0, T60, and T120 minutes post-glucose infusion. ARB increased Nrf2 binding 32% compared to OLETF at T60. Total superoxide dismutase (SOD) and catalase (CAT) activities were increased 45% and 66% respectively in ARB treated animals compared to OLETF. Mitochondrial enzyme activities of aconitase, complex I, and complex II increased by 135%, 33% and 66%, respectively in ARB compared to OLETF. These data demonstrate the protective effects of AT1 blockade on mitochondrial function during the manifestation of insulin resistance suggesting that the inappropriate activation of AT1 during insulin resistance may impair Nrf2 translocation and subsequent antioxidant activities and mitochondrial function.

Water-soluble NNN-pincer complexes of cobalt, nickel and palladium: Solid-state structures and catalytic activity

Neutral NNN-pincer ligand 1 based on a pyridyl core and cyclic amidine pendant arms was synthesized via a straightforward condensation reaction. Its square-planar palladium acetate complex 2 was prepared in methanol and featured a cyclic, hexameric solid-state structure assembled through moderately strong N⋯H⋯O hydrogen bonds involving the ligand backbone and the non-coordinated acetate group. The octahedral, diamagnetic Co(III) complex 3 was prepared via in-situ air oxidation of its Co(II) analog. Its solid-state structure confirmed the oxidation state of the metal and revealed the presence of weak bridging and terminal NH⋯Cl hydrogen bonds. Paramagnetic nickel complex 4 was prepared in a similar fashion to 1 and was postulated to have a covalent attachment of the acetate moieties to the metal. Derivatives 2 and 3 had excellent water solubility and stability while 4 was sparingly soluble in water. Cyclic voltammetry revealed electrochemically reversible electron transfer steps corresponding to the Co(II)/Co(III) and Ni(II)/Ni(III) redox couples at −0.31V and 1.04V versus SHE, respectively. Complex 4 displayed catalytic competency towards the thiolation of iodobenzene with dimethyldisulfide and zinc in DMF. In water, 4 was able to catalyze the Negishi cross-coupling of iodobenzene.

Electrochemically-driven benzo[a]pyrene metabolism via human cytochrome P450 1A1 with reductase coated nitrogen-doped graphene nano-composites

Benzo[a]pyrene (BaP), one of polycyclic aromatic hydrocarbons (PAHs), is identified as a prime carcinogen. Enzymatic metabolite of BaP diol epoxide is one of the important factors in its carcinogenic effect. Herein, cytochrome P450 1A1 modified nitrogen-doped graphene was synthesized to study the BaP metabolism with electrochemically-driven pathway. The direct and reversible electron transfer of the immobilized CYP1A1 on pyrenebutyric acid modified nitrogen-doped graphene nanocomposites was observed with an apparent electron transfer constant of 0.53s−1, and formal potential of −0.48V. With addition of BaP to an air-saturated buffer, the reduction peak current of dissolved oxygen increased, which confirmed the catalytic behavior of CYP1A1 to BaP. The Michaelis-Menten constant (Kmapp) and heterogeneous reaction rate constant of the catalytical reaction were calculated to be 25.6μM and 1.9s−1, respectively. The inhibition effects of alpha-naphthoflavone on CYP1A1 catalyze-cycle were also illustrated with the IC50 value of 1.2μM. The enzyme-induced BaP metabolism could be further demonstrated by the high performance liquid chromatography (HPLC) and gas chromatography-mass spectra (GC/MS). All these results showed that the proposed system had potential application for the development of drug discovery and the prediction of the chemicals toxicity in food and environment.

Ultrafast Electron Transfer from Upper Excited State of Encapsulated Azulenes to Acceptors across an Organic Molecular Wall

In the context of generating reactive organic radical cations within a confined capsule and exploring photoinduced electron transfer from encapsulated organic molecules to organic and inorganic acceptors through an organic molecular wall, we have investigated electron transfer from the upper excited state (S2) of azulene (Az) and guaiazulene (GAz) enclosed within an octa acid (OA) capsule to water-soluble 4,4′-dimethyl viologen2+ (MV2+) and pyridinium+ (Py+) salts or colloidal TiO2. S2 fluorescence of OA encapsulated Az and GAz was quenched by electron acceptors such as MV2+ and Py+ salts. That electron transfer is responsible for S2 fluorescence quenching was established by recording the transient absorption spectrum of the MV●+ in the femtosecond time regime. Femtosecond time-resolved fluorescence experiments suggested that the time constant for the forward and reverse electron transfer from encapsulated Az and GAz to MV2+ is 4 and 3.6 ps, and 55.7 and 36.9 ps, respectively. The observed S2 fluorescence...

Mitochondrial permeability transition pore: sensitivity to opening and mechanistic dependence on substrate availability

Mitochondrial Ca2+ uptake has a key role in cellular Ca2+ homeostasis. Excessive matrix Ca2+ concentrations, especially when coincident with oxidative stress, precipitate opening of an inner mitochondrial membrane, high-conductance channel: the mitochondrial permeability transition pore (mPTP). mPTP opening has been implicated as a final cell death pathway in numerous diseases and therefore understanding conditions dictating mPTP opening is crucial for developing targeted therapies. Here, we have investigated the impact of mitochondrial metabolic state on the probability and consequences of mPTP opening. Isolated mitochondria were energised using NADH- or FADH2-linked substrates. The functional consequences of Ca2+-induced mPTP opening were assessed by Ca2+ retention capacity, using fluorescence-based analysis, and simultaneous measurements of mitochondrial Ca2+ handling, membrane potential, respiratory rate and production of reactive oxygen species (ROS). Succinate-induced, membrane potential-dependent reverse electron transfer sensitised mitochondria to mPTP opening. mPTP-induced depolarisation under succinate subsequently inhibited reverse electron transfer. Complex I-driven respiration was reduced after mPTP opening but sustained in the presence of complex II-linked substrates, consistent with inhibition of complex I-supported respiration by leakage of matrix NADH. Additionally, ROS generated at complex III did not sensitise mitochondria to mPTP opening. Thus, cellular metabolic fluxes and metabolic environment dictate mitochondrial functional response to Ca2+ overload.

Polyoxometalate Heterogeneous Nanostructures As Cathodes for Mg2+ Ion Storage

As global energy demands continue to rise each year, current state-of-the-art Li-ion battery (LIB) systems are predicted to reach the limit in the amount of energy that they can supply. In addition to this, LIBs are also limited by the low resource availability of Li metal. One proposed solution is to move away from LIBs to multivalent ion systems; of these alternatives, magnesium (Mg) is considered a promising material for the next generation of rechargeable batteries. Unlike Li, Mg metal does not form dendritic structures during cycling which would allow it to be employed as an anode which has a specific capacity of 2205 mAh/g compared to 777 mAh/g of the graphite anode that is currently used in LIBs. Mg also has a very high elemental abundance in the earth’s crust (2.44x104 ppm) which would drive down the production cost while simultaneously ensuring the longevity of these batteries in terms resource availability. Most importantly, the divalent nature of the Mg-ion means that it can carry twice the amount of charge per ion compared to Li. This is largely related to the high volumetric capacity (3833 mAh/ml) of Mg which is superior to even that of Li metal. While there is potential for Mg to replace LIBs, commercialization of these batteries has been hindered by sluggish insertion kinetics into cathode host materials as a direct result of the strong coulombic interactions experienced by the divalent Mg-ion. Due to this drawback, conventional metal oxide or sulfide insertion cathodes for Mg batteries tend to exhibit low capacities and operating voltages. In response to this, a large portion of Mg battery research is currently focused on the development of novel materials capable of functioning as cathodes for fast and efficient Mg-ion insertion. The idea proposed in this work is to depart from the conventional intercalation mechanism of LIBs and move towards a molecular cluster battery (MCB) based on polyoxometalate (POM) metal oxygen cluster molecules of early transition metals (Mo, W, V, or Nb). The unique redox activity of POMs are due to their intrinsic ability to form highly stable reduced and oxidized species allowing them to partake in fast reversible electron transfer reactions. Although POMs are also able to function as electron reservoirs, POMs themselves have negligible electronic conductivity as well as high solubility in both aqueous and organic media. Therefore, in order for these materials to be used as electrodes for electrochemical energy storage, they must first undergo hybridization with highly conductive insoluble substrates such as conductive organic polymers (COPs) or multi-walled carbon nanotubes (MWCNTs). The fabrication of heterogenous cathodes provide a “wiring” effect by electrically connecting the POM molecules allowing them all to take part in the redox chemistry while simultaneously anchoring them to a substrate, thus preventing any loss of active material to electrolyte dissolution during cycling. By taking advantage of the synergistic effect of pairing the ionically conductive POM molecule with the electrically conductive substrate; the resulting cathode material will thus be capable of fast electron transfer reactions with high ionic mobility. In this work, hybrid nanostructured electrodes of poly-3,4-ethylenedioxythiophene (PEDOT) and a phosphomolybdic acid (H3PMo12O40) POM have been fabricated electrochemically and applied as cathodes for Mg-ion storage. Preliminary cyclic voltammetry and galvanostatic cycling data have demonstrated an enhancement in the capacity of the PEDOT cathode after integration of the POM molecules throughout the polymer matrix. The initial cycling studies have also shown that the PEDOT-POM redox peaks are still present after 7 days of soaking in the organic electrolyte which suggests that the POM molecules do not readily dissolve out of the PEDOT matrix. This work highlights the potential of redox active POM inorganic clusters to function as cathodes with the capability of advancing the current state of Mg batteries.

Photoinduced Reversible Electron Transfer Between the Benzhydryl Radical and Benzhydryl Cation in Amorphous Water-Ice.

The benzhydryl radical is generated in high yields by flash-vacuum thermolysis of 1,1,2,2-tetraphenylethane with subsequent trapping of the product in argon or amorphous water at 3-4 K. Photoionization of the radical with various UV lights and electron sources produces the benzhydryl cation, which was identified by IR and UV-vis spectroscopy. In solid argon, the formation of the benzhydryl cation is irreversible, whereas in amorphous water-ice the electron transfer is reversible, and irradiation into the major absorption band at 443 nm of the cation leads back to the radical by electron attachment. Applications of ionization of organic matter trapped in water-ice to icy environments in astrophysics and planetary sciences, including Earth, are discussed.

Electrocatalitic behaviour of serpentinite modified carbon paste electrode

Electrochemistry of carbon paste electrode which contained serpentinite powder and graphite in 1:1 weight ratio was examined in three-electrode cell regarding its electrocatalytic and sensing properties. For this purpose, red-ox reactions of potassium ferrocyanide in aqueous solutions as benchmark media and pesticide tebufenozide (TBF) were examined. Serpentinite characterization performed by XRPD, SEM/EDX, and FTIR confirmed the structure typical for this mineral rock. Voltammetric analyses have in all cases shown that serpentinite modified carbon paste electrode (S-CPE) possess superior electrocatalytic activity in contrast to bare CPE for the red-ox reactions of K4[Fe(CN)6]. The enlargement of the peak currents, higher electroactive surface area, and the decline of the peak-to-peak separation are a proof of reversible and faster electron transfer kinetics for S-CPE. The effect of pH on the electrochemical behaviour of TBF was investigated in Britton-Robinson buffer solutions in range from 2.0 to 7.0 and showed the best analytical performance at pH5.0. The oxidation peak of TBF appeared at +0.5V vs. Ag/AgCl under conditions optimized for the determination of TBF in the differential pulse stripping voltammetry: initial potential +0.1V, end potential +0.9V, accumulation potential −0.35V, accumulation time 120s, and the scan rate 50mVs−1.

Reversibility of Ketone Reduction by SmI2–Water and Formation of Organosamarium Intermediates

The reduction of ketones by SmI2–water has long been thought to proceed through a reversible initial electron transfer with the formation of organosamarium intermediates in a follow-up step. Kinetic experiments on the reduction of two model ketones and structurally similar ketones with a pendant alkene are shown to be consistent with a rate-limiting reduction by SmI2–water through a proton-coupled electron-transfer (PCET). Literature values for the rates of radical cyclizations and reduction of radicals by SmI2 and thermochemical data for radical reduction by SmI2–water further support a rate-limiting initial step for ketone reductions. These data suggest that discrete organosamarium species may not be intermediates in ketone reductions by SmI2–water.

The «in vivo» study of blood 5-fluorouracil content by quenching of intrinsic protein fluorescence

The dynamics of blood fluorescence (FL) after intravenous injection of 5-fluorouracil (FU) to oncology patients taking chemotherapy were investigated. It was demonstrated that FU quenches FL of water solutions of tryptophan (Trp) (total concentration is 1.0 × 10−5molL−1, λmax = 353nm) and plasma protein – albumin (λmax = 340nm) with the Stern–Volmer constants 16.4 × 103Lmol−1 and 52Lmol−1, accordingly. The quenching of both Trp and albumin FL by 5-fluorouracil was concluded to proceed via the static mechanism of reversible photoinduced electron transfer (PET).

Reversible Bond/Cation-Coupled Electron Transfer on Phenylenediamine-Based Rhodamine B and Its Application on Electrochromism.

A biomimetic system on reversible bond-coupled electron transfer (BCET) has been proposed and investigated in a switchable Rh-N molecule with redox active subunits. We discover that energy barrier of C-N bond breaking is reduced dramatically to less than 1/7 (from 40.4 to 5.5 kcal/mol), and 1/3 of the oxidation potential is simultaneously lowered (from 0.67 to 0.43 V) with the oxidation of Rh-N. The concept, cation-coupled electron transfer (CCET), is highly recommended by analyzing existing proton coupled electron transfer (PCET) and metal coupled electron transfer (MCET) along with aforementioned BCET, which have same characteristic of transferring positive charges, such as proton, metal ion, and organic cation. Molecular switch can be controlled directly by electricity through BCET process. Solid electrochromic device was fabricated with extremely high coloration efficiency (720 cm2/C), great reversibility (no degradation for 600 cycles), and quick respond time (30 ms).

Analytical solution of the convection-diffusion equation for uniformly accessible rotating disk electrodes via the homotopy perturbation method

The mathematical problem corresponding to a one-electron reversible electron transfer at a rotating disk electrode is solved under transient and steady state conditions by using the homotopy perturbation method. Analytical solutions for the time-dependent and stationary concentration profiles, current response and diffusion layer are deduced for finite values of the Schmidt number. The solutions enable us to obtain the response in chronoamperometry, normal pulse voltammetry and steady state voltammetry. The analytical results are assessed by comparison with previous analytical solutions for limiting cases as well as with numerical simulations, finding a satisfactory agreement.

π-Extended and Curved Antiaromatic Polycyclic Hydrocarbons.

Synthesis of antiaromatic polycyclic hydrocarbons (PHs) is challenging because the high energy of their highest occupied molecular orbital and low energy of their lowest unoccupied molecular orbital cause them to be reactive and unstable. In this work, two large antiaromatic acene analogues, namely, cyclopenta[pqr]indeno[2,1,7-ijk]tetraphene (CIT, 1a) and cyclopenta[pqr]indeno[7,1,2-cde]picene (CIP, 1b), as well as a curved antiaromatic molecule with 48 π-electrons, dibenzo[a,c]diindeno[7,1,2-fgh:7',1',2'-mno]phenanthro[9,10-k]tetraphene (DPT, 1c), are synthesized on the basis of the corona of indeno[1,2-b]fluorene. These three antiaromatic PHs possess a narrow energy gap down to 1.55 eV and exhibit high kinetic stability under ambient conditions. Moreover, these compounds display reversible electron transfer processes in both the cathodic and anodic regimes. Their cation and anion radicals are characterized by in situ vis-NIR absorption and electron paramagnetic resonance spectroelectrochemistry. The X-ray crystallographic analysis confirms that while CIP and CIT manifest planar structures, DPT shows a curved π-conjugated carbon skeleton. The synthetic strategy starting from ortho-substituted benzene units to construct five-membered rings in this work provides a unique entry to novel pentagon-embedding or curved antiaromatic polycyclic hydrocarbons. In addition, besides the detailed chemical and physical investigations, microscale single-crystal fiber field-effect transistors were also fabricated.

Luminescent characterization of interaction efficiency between (−)-cytisine and amino acids an indicator of anti-inflammatory of some 12-N-substituted (−)-cytisine derivatives

Abstract In the present work, the spectral fluorescent properties of N-R-12-N-methylcytisine-3-amines (R = 2-furylmethyl, 2-hydroxybenzyl, 2-thienylmethyl and 2-phenylprop-2-en-1-yl) have been studied and their relative quantum yields and lifetimes in the electronically excited states have been defined. These compounds have bioactivity as potential inhibitors of cyclooxygenase-2 (COX-2). We have studied the quenching of fluorescence (FL) of L-tyrosine (Tyr) and L-tryptophan (Trp) by amino-derivatives of 12-N-methylcytisine as well as the FL quenching of cytisines themselves by L-serine (Ser) and L-arginine (Arg). The found Stern–Volmer constants and lifetimes of the excited states reveal static mechanism of the quenching of aromatic amino acids and dynamic mechanism for the FL quenching of cytisines by Arg (Ser does not quench FL) due to the reversible photo-induced electron transfer (PET). The thermodynamic assessment of the PET probability according to the Weller equation agrees with the observed regularities and series of bioactivity of the cytisines. Using molecular docking, we have found the most probable positions of the 12-N-methylcytisine derivatives in the active site of COX-2 where their stacking interactions with Trp387 and Tyr385 and hydrogen bonding with Arg120 and Ser530 occur. As the mentioned amino acids play a key role in the complexion of the studied compounds by COX-2, we have proposed that bioactivity mechanism of the lead compounds implies the COX-2 inhibition by the withdrawal of electron from electron-transfer processes in the chain HEM–His388–Trp387–His386–Tyr385 resulted from their stacking interactions with Trp and/or Tyr.

Further investigation of the equivalence of staircase and linear scan voltammograms. I- Sampling conditions for reversible reactions involving soluble species

Since the pioneering work by Osteryoung et al., J. Electroanal. Chem. 222 (1987) 69, the discussion about the equivalence of staircase and linear scan voltammograms is based on the ‘Abelian’ or ‘non-Abelian’ feature of the integral equation used for modelling the voltammetric response of redox systems. In practice, further investigation is required for prediction of the optimal value of current sampling parameter (γopt) that guarantees the equivalence of voltammetric and staircase voltammetric data. This first article focuses on reversible electron transfer reactions involving soluble species. The discussion is based on integral-equation-based models and the use of local/global criteria for the comparison of staircase and linear scan voltammograms. Main results in the article and the Supporting information joined should concern the dependence of γopt on the electrode potential, the potential step amplitude of staircase signal, the reaction scheme, and the mass transport process involved.

Electron transfer from the perspective of electron transmission: Biased non-adiabatic intermolecular reactions in the single-particle picture.

In this work, we revisit Hopfield's formulation of non-adiabatic electron transfer between uncorrelated redox species within the single-particle picture description of electron transmission commonly applied in solid-state systems. The formulation is applied to a model system, similar to that often found in solid-state electron tunneling studies, consisting of redox species separated by an insulating tunneling barrier. Redox tunneling across such an insulator is predicted to demonstrate a marked asymmetry, ranging from one to three orders of magnitude between forward and reverse bias electron transfer rates, when reactants possess dissimilar reorganization energies. This significant asymmetry is shown to arise from trapezoidal reshaping of the integrated Gamow tunneling barrier and corresponding transmission probability under an applied bias. In general, this work aims to further bridge concepts between the electron transfer and transport communities.

Intramolecular Light-Driven Accumulation of Reduction Equivalents by Proton-Coupled Electron Transfer.

The photochemistry of a molecular pentad composed of a central anthraquinone (AQ) acceptor flanked by two Ru(bpy)32+ photosensitizers and two peripheral triarylamine (TAA) donors was investigated by transient IR and UV-vis spectroscopies in the presence of 0.2 M p-toluenesulfonic acid (TsOH) in deaerated acetonitrile. In ∼15% of all excited pentad molecules, AQ is converted to its hydroquinone form (AQH2) via reversible intramolecular electron transfer from the two TAA units (τ = 65 ps), followed by intermolecular proton transfer from TsOH (τ ≈ 3 ns for the first step). Although the light-driven accumulation of reduction equivalents occurs through a sequence of electron and proton transfer steps, the resulting photoproduct decays via concerted PCET (τ = 4.7 μs) with an H/D kinetic isotope effect of 1.4 ± 0.2. Moreover, the reoxidation of AQH2 seems to take place via a double electron transfer step involving both TAA+ units rather than sequential single electron transfer events. Thus, the overall charge-recombination reaction seems to involve a concerted proton-coupled two-electron oxidation of AQH2. The comparison of experimental data obtained in neat acetonitrile with data from acidic solutions suggests that the inverted driving-force effect can play a crucial role for obtaining long-lived photoproducts resulting from multiphoton, multielectron processes. Our pentad provides the first example of light-driven accumulation of reduction equivalents stabilized by PCET in artificial molecular systems without sacrificial reagents. Our study provides fundamental insight into how light-driven multielectron redox chemistry, for example the reduction of CO2 or the oxidation of H2O, can potentially be performed without sacrificial reagents.