Electron Transfer Reduction Research Articles

Triplet-Excited Riboflavin Promotes Labile Fe(III) Accumulation and Changes Mineralization Pathways in Fe(II)-Catalyzed Ferrihydrite Transformation.

Flavins are well-known endogenous electron shuttles that facilitate long-distance extracellular electron transfer in dissimilatory iron reduction (DIR), but the effects of their photosensitivity on DIR and the transformation of metastable iron (oxyhydr)oxides like ferrihydrite (Fh) remain underexplored. This study compared the kinetics, pathways, and products of Fh transformation catalyzed by aqueous Fe(II) (Fe(II)aq) in the presence of oxidized riboflavin (RFox) at pH 7 under both dark and light conditions. While RFox has a negligible impact on Fe(II)-catalyzed Fh transformation in the dark, its photoexcited triplet state (3RF*) can significantly accelerate interfacial electron transfer (IET) from Fe(II)aq to Fh, increasing the reductive dissolution rate of Fh and boosting the accumulation rate of the key intermediate labile Fe(III) (Fe(III)labile) from 14.2 μM·h-1 to 35.6 μM·h-1. The 3RF*-promoted Fe(II)-Fh IET favors the oxolation of Fe(III)labile to lepidocrocite (Lp) over goethite (Gt) formation during Fh transformation and promotes the subsequent conversion of Lp to magnetite (Mt), altering the mineral products from sole Gt to a mixture of Lp (24.1%), Gt (45.4%), and Mt (30.5%). These findings highlight the notable effects of riboflavin as a photosensitizer on Fh biotransformation, with implications for microbial respiration and elemental cycling in natural environments.

Homogeneous electrochemiluminescence biosensor for hyaluronidase based on the regulation of hyaluronic acid coating on magnetic nanoparticles

A homogeneous electrochemiluminescence (ECL) sensor for hyaluronidase (HAase) detection was developed by controlling the coating of hyaluronic acid (HA) on the surface of magnetic ECL nanoparticles (NPs). Initially, Fe3O4@Ru@SiO2 NPs with magnetic properties were synthesized and subsequently coated with HA (Fe3O4@Ru@SiO2-HA). The properties of HA, such as its negative charge and viscosity, induced strong electrostatic repulsion and reduced electron transfer efficiency between the Fe3O4@Ru@SiO2-HA NPs and the negatively charged electrodes. Furthermore, this coating hindered the approach of co-reactants to the NPs, resulting in a diminished ECL signal. In the presence of HAase, HA is hydrolyzed, releasing the Fe3O4@Ru@SiO2 NPs. Magnetic separation minimizes background interference and allows the magnetic ECL NPs to diffuse freely in solution, facilitating electron transfer and reactant interaction, thereby leading to detectable signal changes. The sensor exhibited a linear response to HAase concentration ranging from 5.0 to 60 U/mL, with a detection limit of 1.8 U/mL. This method is rapid, straightforward, and effectively leverages the inherent properties of HA, making it suitable for broad applications in the detection of proteins, enzymes, and other biomarkers.

Free‐Base Octaethylporphyrin on Au(111) as Heterogeneous Organic Molecular Electrocatalyst for Oxygen Reduction Reaction in Acid Media: An Electrochemical Scanning Tunneling Microscopy and Rotating Ring‐Disc Electrode Analyses

The oxygen reduction reaction (ORR) using metal porphyrin catalysts is currently widely explored. Conversely, metal‐free molecular systems are much less investigated, and there is limited information available for molecules such as nonmetalated macrocycles capable of catalyzing the ORR or other small molecules. Herein, the activity and selectivity of a heterogeneous organic molecular electrocatalyst, octaethylporphyrin (H2OEP), adsorbed on Au(111) toward ORR in acidic aqueous electrolyte are investigated. Electrochemical scanning tunneling microscopy (EC‐STM) is employed to monitor the molecular layer during the electrochemical process. Additionally, cyclic and linear sweep voltammetries are performed at still and rotating Pt/ring‐H2OEP‐functionalized Au(111)/disk electrodes to determine the activity and selectivity of the H2OEP monolayer toward ORR on Au(111). Based on EC‐STM and computation analysis, dioxygen electroreduction does not follow an inner‐sphere electron transfer reduction as seen in metal porphyrins, where a preliminary MO2 bond has to form, but it follows an outer‐sphere mechanism involving the precoordination of O2 induced by the protonated hydrogen of the macrocycle cavity.

Reductive Photocatalytic Proton-Coupled Electron Transfer by a Zirconium-Based Molecular Platform.

Reductive proton-coupled electron transfer (PCET) has important energetic implications in numerous synthetic and natural redox processes. The development of catalytic systems that can mediate such transformations has become an attractive target, especially when light is used to generate the reactive species towards solar-to-chemicals conversion. However, such approach becomes challenged by kinetic competition with H2 evolution. Here we describe the excited state reactivity of a molecular Zr-based platform under visible light irradiation for the efficient reduction of multiple bonds. Mechanistic investigations shine light on a charge separation process that colocalizes an excited electron and an acidic proton to promote selective PCET. We further leveraged this reactivity for the photocatalytic reduction of a variety of organic substrates. Our results demonstrate the promise of this molecular platform to design strong photocatalytic PCET mediators for reductive transformations. More broadly, we also show the potential relevance of PCET mechanisms in the (photo)redox chemistry of Zr-based molecular materials.

In-situ cation-exchange deposited Ag2S/In4SnS8 of Z-type heterojunction coupled with DNA recycling amplification for photoelectrochemical biosensing

Herein, a novel photoelectrochemical (PEC) biosensor was developed utilizing an in situ cation-exchange method to deposit a high-performance Ag2S/In4SnS8, a Z-type heterojunction with co-shared S atoms, as a signal indicator and using DNA recycling amplification for the sensitive and accurate detection of miRNA-141. The photosensitive Ag2S deposited on the In4SnS8 surface not only facilitated the rapid generation of photoelectrons but also formed a Z-type heterojunction with In4SnS8, effectively inhibiting electron-hole pair recombination. This resulted in a considerable improvement in the photoelectric conversion efficiency of Ag2S/In4SnS8, yielding an ∼ 120-fold increase in photocurrent compared to that of In4SnS8 under 660-nm visible-light irradiation. Furthermore, the arborescent DNA structure formed by hybrid chain reaction (HCR) enhanced the steric effect, thereby reducing the PEC response. Importantly, numerous quenchers MnPP competed for light absorption and captured photogenerated electrons in the valence bands of In4SnS8 and Ag2S, reducing electron transfer to the electrode and further considerably reducing the photocurrent. This enabled the sensitive detection of miRNA-141 across a concentration range from 10 amol·L−1 to 100 pmol·L−1, with a limit of detection as low as 3.3 amol·L−1 (S/N = 3). The proposed biosensor exhibits excellent stability and is expected to be applied for detecting clinically relevant disease markers.

Effect of operating temperature on ammonia decomposition behavior and cell performance of direct ammonia solid oxide fuel cells

Direct ammonia solid oxide fuel cells (DA-SOFC) are regarded as a promising power generation technology. Nevertheless, the catalytic reaction of ammonia on the anode surface significantly affects DA-SOFC performance. This study explores the deterioration of DA-SOFC performance in the 550–700 °C and the interaction between NH3 decomposition and electrochemical reactions. The findings indicate that, at 550 °C, compared to H2, the reduction in power density of NH3 18.58% exceeds 4.56%t of NH3 d.s.g. (mixtures, 0.75H2 + 0.25N2). The anodic polarization impedance of NH3 exceeds that of H2 and NH3 d.s.g. by 51.1% and 28.9%, respectively. Cathode utilizing O2 has a dual impact on NH3 decomposition, at lower temperatures, oxidizing the anode's active site, decreasing NH3 decomposition rate, resulting in insufficient H2 supply, reducing electron transfer coefficient. Conversely, at higher temperatures, O2 promotes NH3 decomposition by boosting H2 consumption. However, more N2 is produced, increasing the concentration loss.

Enhancement of photocatalytic degradation of ciprofloxacin via constructing conductive matrix

The application of heterogeneous photocatalysts is severely limited by the high charge transfer resistance (Rct). BiVO4/g-C3N4 photocatalysts were prepared and loaded on the conductive matrix material carbon paper (CP) to reduce electron transfer resistance and improve the photocatalytic performance. The Rct of BiVO4/g-C3N4@CP was remarkedly reduced by 94.3 % compared to the photocatalysts on the oil paper (BiVO4/g-C3N4@OP), while the photocurrent density increased by 5.5 times. The utilization efficiency of light energy and separation of photoelectrons and holes were improved with CP due to its ability to facilitate long-distance transfer of photoelectrons. Consequently, the photocatalytic degradation performance of BiVO4/g-C3N4@CP was enhanced by a 26.1 % improvement in ciprofloxacin (CIP) degradation efficiency. Quenching experiment, LC-MS analysis and DFT calculation revealed that piperazine ring opening and C-F cleavage were the major pathways for CIP degradation with BiVO4/g-C3N4@CP.

Core-Shell Structured Cobalt Sulfide/C. I. Pigment Yellow 53 Photocatalysts with Abundant Sulfur Vacancies for Efficient Photocatalytic Co-Production of Xylonic Acid and CO.

Photocatalytic biorefinery has been gaining increasing attention as a promising method for utilizing biomass and solar energy, yet it still faces the key challenge of designing stable, efficient, and cost-effective photocatalysts. In this study, cobalt sulfide/ C. I. Pigment Yellow 53 composite photocatalysts (CoS/PY53-CSx) with a core-shell structure, which has abundant sulfur (S) vacancies, are developed using a simple hydrothermal method. The CoS nanocage with S vacancies not only offers numerous active sites but also enhances the light-trapping performance of PY53. Moreover, the internal electric field within the core-shell CoS/PY53-CSx further enhances charge separation/transfer efficiency while reducing electron transfer resistance, thereby boosting photocatalytic activity. Remarkably, 75.2% of xylonic acid and 22.8µmol of CO from xylose are obtained using CoS/PY53-CS0.1 in an air atmosphere. Recycling experiments demonstrate that CoS/PY53-CS0.1 exhibits excellent recyclability due to the strong bonding force between the core and shell. In addition, electron spin resonance characterization combined with poisoning experiments suggests that h+ and ·O2 - serve as the main oxidation active species during this system. This work presents a simple and cost-effective method for efficient photocatalytic biorefinery.

Enhancing methane production from corn straw via illumination-assisted Fe3O4/g-C3N4 nanocomposite in anaerobic digestion

This study proposes a novel anaerobic digestion (AD) strategy combining recyclable photoactivated nanomaterials with illumination to enhance electronic transfer for anaerobic microorganisms. Results showed that 7000 Lux illumination increased methane production yield and rate. Incorporating Fe3O4 into graphite carbon nitride (g-C3N4) created a recyclable Fe3O4/g-C3N4 (FG) nanocomposite with improved light absorption, conductivity, redox properties, and methane promotion. The highest methane yield from corn straw was achieved with 7000 Lux and 1.5 g/L FG nanocomposite, 22.6% higher than the dark control. The AD system exhibited increased adenosine triphosphate content, improved redox performance, reduced electron transfer resistance, and higher photocurrent intensity. These improvements bolstered the microorganisms and key genes involved in hydrolysis and acidification, which in turn optimized the acetoclastic pathway. Furthermore, this strategy promoted microorganisms associated with direct interspecies electron transfer, fostering a favorable environment for methanogenic activities, paving the way for future anaerobic reactor developments.

Phytic acid inhibits Cr(VI) reduction on Fe(II)-bearing clay minerals: Changing reduction sites and electron transfer pathways

The presence of organic phosphorus may influence the characteristics of Cr(VI) reduction and immobilization on Fe(II)-bearing clay minerals under anoxic conditions, as the organic phosphorus tends to bind strongly to clay minerals in soil. Herein, reduced nontronite (rNAu-2) was used to reduction of Cr(VI) in the presence of phytic acid (IHP) at neutral pH. With IHP concentration from 0 to 500 μM, Cr(VI) reduction decreased obviously (17.8%) within first 5 min, and then preferred to stagnate during 4–12 h (≥50 μM). After that, Cr(VI) was reduced continuously at a slightly faster rate. Density functional theory (DFT) calculations revealed that IHP primarily absorbed at the edge sites of rNAu-2 to form Fe-IHP complexes. X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), and Fourier transform infrared spectroscopy (FTIR) results demonstrated that IHP hindered the ingress of CrO42− into the interlayer space of rNAu-2 and impeded their reduction by trioctahedral Fe(II) and Al-Fe(II) at basal plane sites in the initial stage. Additionally, Fe(II) extraction results showed that IHP promoted the electron from interior transfer to near-edge, but hindered it further transfer to surface, resulting in the inhibition on Cr(VI) reduction at edge sites during the later stage. Consequently, IHP inhibits the reduction and immobilization of Cr(VI) by rNAu-2. Our study offers novel insights into electron transfer pathways during the Cr(VI) reduction by rNAu-2 with coexisting IHP, thereby improve the understanding of the geochemical processes of chromium within the iron cycle in soil.

Study of pyrene-based covalent organic frameworks for efficient photocatalytic oxidation of low-concentration NO

This research presents the development of innovative pyrene-based COFs aimed at enhancing photocatalytic oxidation of low-concentration nitrogen oxide. By precisely modifying the structural length and incorporating additional functional groups into pyrene-based COFs, we identified TAPPy-DMTP-COF as the most effective performer. This COF, characterized by its shortest length and the presence of -OCH3 functional groups, demonstrated superior performance, likely due to reduced electron transfer resistance and the presence of additional oxygen active sites. Building on the potential of TAPPy-DMTP-COF, we developed a covalently linked Type-II heterostructure with g-C3N4. The resulting heterostructure, 40TAPPy-DMTP-COF/g-C3N4, with a 40 % mass fraction of TAPPy-DMTP-COF, was confirmed using SEM, XRD, and other techniques. It exhibited an exceptional photocatalytic efficiency of 45.8 % and NO3- selectivity of 97.4 %. This remarkable performance can be attributed to improved electron communication facilitated by chemical bonding, as confirmed by XPS results. Additionally, the optimized heterostructure interface not only improved electron transfer but also inhibited the recombination of electron-hole pairs. The growth of TAPPy-DMTP-COF on the surface of g-C3N4 significantly enhanced visible light absorption, as confirmed by UV–vis spectroscopy. This study not only underscores the importance of precise control over the structural features of pyrene-based COFs but also introduces a novel approach for enhancing NO oxidation. By constructing a covalently linked Type-II heterostructure, we have significantly enhanced the interface interaction within the heterostructure, leading to superior photocatalytic performance.

Biochar modulates intracellular electron transfer for nitrate reduction in denitrifying anaerobic methane oxidizing archaea

Denitrifying anaerobic methane oxidizing (DAMO) archaea plays a significant role in simultaneously nitrogen removal and methane mitigation, yet its limited metabolic activity hinders engineering applications. This study employed biochar to explore its potential for enhancing the metabolic activity and nitrate reduction capacity of DAMO microorganisms. Sawdust biochar (7 g/L) was found to increase the nitrate reduction rate by 2.85 times, although it did not affect the nitrite reduction rate individually. Scanning electron microscopy (SEM) and fluorescence excitation-emission matrix (EEM) analyses revealed that biochar promoted microbial aggregation, and stimulated the secretion of extracellular polymeric substances (EPS). Moreover, biochar bolstered the redox capacity and conductivity of the biofilm, notably enhancing the activity of the electron transfer system by 1.65 times. Key genes involved in intracellular electron transport (Hdr, MHC, Rnf) and membrane transport proteins (BBP, ABC, NDH) of archaea were significantly up-regulated. These findings suggest that biochar regulates electrons generated by reverse methanogenesis to the membrane for nitrate reduction.

Interfacially Enhanced Superconductivity in Fe(Te,Se)/Bi4Te3 Heterostructures.

Realizing topological superconductivity by integrating high-transition-temperature (TC) superconductors with topological insulators can open new paths for quantum computing applications. Here, a new approach is reported for increasing the superconducting transition temperature by interfacing the unconventional superconductor Fe(Te,Se) with the topological insulator Bi-Te system in the low-Se doping regime, near where superconductivity vanishes in the bulk. The critical finding is that the of Fe(Te,Se) increases from nominally non-superconducting to as high as 12.5K when Bi2Te3 is replaced with the topological phase Bi4Te3. Interfacing Fe(Te,Se) with Bi4Te3 is also found to be critical for stabilizing superconductivity in monolayer films where can be as high as 6K. Measurements of the electronic and crystalline structure of the Bi4Te3 layer reveal that a large electron transfer, epitaxial strain, and novel chemical reduction processes are critical factors for the enhancement of superconductivity. This novel route for enhancing TC in an important epitaxial system provides new insight on the nature of interfacial superconductivity and a platform to identify and utilize new electronic phases.

Photocatalytic [3+2] Cycloaddition of Alkyl/aryl Iodides and Internal Alkynes by Merging Halogen and Hydrogen Atom Transfer

Comprehensive SummaryA visible light photocatalytic [3+2] cycloaddition of alkynes with readily accessible organic iodides as the C3 synthon is developed herein. By merging halogen atom transfer (XAT) and hydrogen atom transfer (HAT), alkyl/aryl iodides serve as a formal diradical precursor and add across C‐C triple bonds to deliver a number of functionalized cyclopentanes in moderate to high yields with exceptional regio‐ and diastereoselectivity. A reductive radical‐polar crossover mechanism, involving the cascade XAT, radical addition, 1,5‐HAT, polar effect‐promoted 5‐endo annulation, single electron transfer (SET) reduction, and protonation, may account for this unprecedented dehalogenative [3+2] cycloaddition. This work not only expands the repertoire of the traditional RATC methodology, but also provides a robust platform for the expedient assembly of cyclopentanes, a valuable structural motif in the realms of medicinal chemistry and material sciences.

Photocatalytic efficiency of GO-based Ti-doped Co3O4 nanosheets for mixed dyes and the effects of oxidizing and reducing reagents

The hydrothermal technique was used to synthesize the GO-based Ti-doped Co3O4 nanosheets and investigate their photocatalytic properties. These synthesized smart and active materials degraded the mixed dyes of Methylene orange (MO) and Methylene blue (MB) under the sunlight within 180 min with an effective efficiency of 94.85 %. Various physical parameters were studied by using distinct characterization techniques related to structural, compositional, optical, and I–V characteristics. The effects of Young's modulus, stiffness, bulk modulus, microstrain, stacking fault, and dislocation density were studied in detail. The conversion of phase was identified by using Raman spectroscopy. The effects of band gap, surface area, and photosensitivity were illustrated thoroughly. The effect of scavengers on the photocatalytic efficiency was observed and it was concluded that both electrons and holes are activated during the photocatalytic activity. The doping of Ti has played a crucial role in enhancing surface area, electron transfer rate, photosensitivity, and reduction in the bandgap. These smart materials are also useful for photodetector applications.

Enhanced electroreduction of low-concentration nitrate using a Cu-Pd bimetallic cathode system: Performance evaluation, mechanism analysis, and potential applications

Copper (Cu) is a widely recognized cathode for the electrochemical reduction of nitrate (NO3-). Nevertheless, its practical applications are currently restricted due to limited activity and selectivity, particularly at low NO3- concentrations. Herein, a Cu-Pd bimetallic cathode system was designed for NO3- reduction reaction with low NO3- concentrations (≤40 mg-N L−1). In this system, a Cu nanowire array cathode was utilized for NO3- reduction, while a Pd/C particle cathode was employed for NO2- reduction with H2 generated in situ from a polypyrrole electrode. Due to the improved mass transfer and active sites derived from Pd/C particle cathode, along with the synergistic effects of NO3- reduction and NO2- reduction, the constructed Cu-Pd bimetallic cathode system achieved a 7.32-fold increase in NO3– removal rate and a 1.70-fold increase in NH4+ selectivity compared to the traditional Cu cathode. This performance surpassed that of many other state-of-the-art Cu-based cathodes under similar conditions. Moreover, the Cu-Pd bimetallic cathode system displayed high reusability, and extremely low Cu and Pd leaching. Additionally, it showed strong resistance to environmental factors and can adapt to a wide pH range (3−9) and various NO3- concentrations (10–40 mg-N L−1). The electron spin resonance and scavenger experiments confirmed that both direct electron transfer and indirect reduction by atomic H* were involved in the NO3- removal process, with indirect reduction playing a more significant role. Overall, our findings guide the design of superior catalytic systems for NO3- removal to enhance the activity and selectivity of NO3- reduction for efficient water purification.

Facile synthesis of MOF–808/RGO-based 3D macroscopic aerogel for enhanced photoreduction CO2

Three-dimensional (3D) macroscopic aerogels have emerged as a critical component in the realm of photocatalysis. Maximizing the integration of materials can result in enhanced efficiency and selectivity in photocatalytic processes. In this investigation, we fabricated MOF-808/reduced graphene oxide (RGO) 3D macroscopic aerogel composite materials employing the techniques of hydrothermal synthesis and freeze-drying. The results revealed that the macroscopic aerogel material exhibited the highest performance in CO2 reduction to CO, particularly when the concentration of RGO was maintained at 5 mg mL−1. In addition, we synthesized powder materials of MR-5 composite photocatalysts and conducted a comparative analysis in terms of photocatalytic CO2 reduction performance and electron transfer efficiency. The results showthat the macroscopic aerogel material boasts a high specific surface area, an abundant internal pore structure, and increased active sites. These attributes collectively enhance light energy utilization, and electron transfer rates, thereby, improving photothermal and photoelectric conversion efficiencies. Furthermore, we conducted in-situ FT-IR measurements and found that the M/R-5 aerogel exhibited the best CO2 adsorption capacity under a CO2 flow rate of 10 mL min−1. The density functional theory results demonstrate the correlation between the formation pathway of the product and the charge transfer pathway. This study provides useful ideas for realizing photocatalytic CO2 reduction of macroscopic aerogel materials in gas–solid reaction mode.

Effect of lattice water on the photochromic property/photochromism of a Zn(II)-viologen coordination polymers

Electron transfer is crucial for the rapid response of viologen-based complexes and investigating the factors that affect electron transfer has always been a major challenge. Herein, a new viologen-based complex, formulated as {[Zn5(cbbbc)3(BTC)3(μ1,1-OH)(H2O)5]·22H2O}n, with a three-dimensional framework was successfully designed and synthesized by viologen ligand 1-(3-carboxybenzyl)-4,4′-bipyridinium chloride (Hcbbpy), trimesic acid (H3BTC) and Zn(NO3)2·6H2O. In particular, complex 1 does not exhibit photochromic properties. However, samples of complex 1 heated at 120 and 180 ℃ display tunable colors under UV light irradiation. The experimental results indicate that the compound's light response is less sensitive with higher water content in the lattice. The polarity and hydrogen bonding ability of lattice water in viologen-based complexes can interact with the donor of viologen, leading to a reduction in electron transfer. This study demonstrates the impact of lattice water on electron transfer in viologen-based complexes and offers insights for designing faster response complexes in the future.

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.

Investigation of the Excited-State Electron Transfer and Cage Escape Yields Between Halides and a Fe(III) Photosensitizer.

Excited-state quenching and reduction of [Fe(phtmeimb)2]+, where phtmeimb is phenyl[tris(3-methyl-imidazolin-2-ylidene)]borate, with iodide, bromide, and chloride were studied in dichloromethane, acetonitrile, and acetonitrile/water 1:1 mixture by means of steady-state and time-resolved spectroscopic techniques. Quenching rate constants were almost diffusion-limited in dichloromethane and acetonitrile and followed the expected periodic trend, i.e., I- > Br- > Cl-. Confirmation of excited-state reductive electron transfer was only unambiguously obtained when iodide was used as a quencher. The cage escape yields, i.e., the separation of the geminate radical pair formed upon bimolecular excited-state electron transfer, were determined. These yields were larger in dichloromethane (0.079) than in acetonitrile (0.017), and no photoproduct could be observed in acetonitrile/water 1:1. This study further emphasizes that solvents with low dielectric constant are more suited for productive excited-state electron transfer using Fe(III) photosensitizers with 2LMCT excited state.