While surface modifications are widely pursued to improve antimicrobial performance of photocatalytic nanoparticles (NPs), the particle-membrane interactions responsible for these effects remain underexplored. We address this gap by investigating the influence of coating TiO2 NPs with the cationic polymer poly-(2-(dimethylamino)-ethyl methacrylate) methyl chloride quaternary salt (qPDMAEMA). In contrast to bare TiO2, the coated NPs adsorb extensively to negatively charged bacteria and bacteria-like membranes, boosting membrane permeabilization upon UV illumination due to formation of reactive oxygen species (ROS). The qPDMAEMA coating was demonstrated not to interfere with ROS formation and to withstand UV illumination over time-scales sufficient for membrane binding and disruption. Such effects were highly localized near membrane-bound NPs, consistent with the short diffusion lengths of ROS (≈10 nm for hydroxyl radicals) and the formation of oxidative membrane 'hot-spots' in the corresponding vicinity of membrane regions where preferential (localized) NP binding occurs. Such preferential localization is demonstrated to occur at poles and nodes of Escherichia coli bacteria. Hypothesizing this to be driven by colocalization with anionic cardiolipin, studies with giant vesicles containing cardiolipin either uniformly distributed or present in segregated domains showed that the polymer-coated TiO2 NPs preferentially bind to cardiolipin-rich regions of the membrane. Together, these results expand on conventional studies of NP interactions with bacteria and bacteria-like membranes and demonstrate that localized interactions must be considered in studies of bacterial membrane interactions of photocatalytic NPs.

We developed N-doped carbon quantum dots (N-CQDs) as both photocathode modifiers and electrolytes for self-powered portable photoelectrochemical (PEC) cells to generate electricity under visible-light illumination. Using betaine-type Meldonium precursor, and either ethylenediamine, N,N-dimethylformamide or NH3·H2O as a nitrogen source deliver three different N-CQDs featuring both surface-negatively-charged and positively-charged groups. Due to structural-directing template functionality of ethylenediamine, N-CQDs(en) incorporates the highest pyridinic-N content, which facilitates the charge conductivity and fine-regulates the reaction selectivity within Csp2-frameworks. As semiconductor-coatings electrodeposited on Cu2O, N-CQDs(en) integrate with Cu2O into heterojunctions (N-CQDs(en)/Cu2O) to improve charge separation and promote 4e- oxygen-reduction into water. Importantly, encapsulating an aqueous solution containing N-CQDs(en) in a gelatin/sodium L-pyroglutamate-derived conductor gives a quasi-solid-state electrolyte that facilitates the charge migration, improving the electrodes-electrolytes interfacial incompatibility, while also possibly helping to in situ complement active sites on the modified photocathode. Coupled with a FeNiOOH/FeN-decorated BiVO4 photoanode, enabling the efficient 4e- water oxidation, the complete system establishes a self-sustaining H2O-O2-H2O cycle. The resulting PEC cell shows impressive electricity output for over 120 h under irradiation, enough to power some small electronics. Unlike conventional photovoltaics, this cell is moisture-tolerant, oxidation-resistant and concurrently harnesses light and chemical energy, presenting a new paradigm for next-generation light-to-electricity conversion.

Understanding the structure of Ru(V)-oxo species is crucial for designing novel catalysts for sustainable energy applications, such as water splitting for green hydrogen production. This study reports the EPR detection of a Ru(V)-oxo intermediate stabilized by terpyridine and phenanthroline carboxylate ligands. The interaction between the carboxylate group and the ruthenium center, along with PCET-dependent hemilability under oxidative conditions, plays a critical role in achieving the high-valent state. Subtle changes in the coordination environment around the central metal also proved to be essential. Low-temperature NMR, high-resolution mass spectrometry, UV-Vis spectroscopy, and density functional theory calculations support these findings.

CO2 conversion to value-added chemicals is a crucial technology toward carbon-neutral fuels. Photocatalysis using sunlight is an energy-efficient alternative to electrochemical and thermal CO2 reduction. Photocatalysts usually yield either CO or formate with varying degrees of selectivity. Herein, a lanthanide-based photocatalytic platform producing CO with the highest turnover to date is reported. The catalyst consists of a pendant amine for CO2 capture and a light-harvesting sensitizer that generates the reactive divalent lanthanide center. CO2 reduction to CO was possible with high selectivity and reactivity by virtue of a distinct mechanistic pathway involving Sm(II), carbamate, and CO2,- as identified intermediates. Attractive (bi)carbonate CO2 feedstocks were efficiently converted to CO. Depending on the conditions, the selective synthesis of formate, methane, and methanol was also possible, demonstrating the wide utility of the platform.

Industrial dinitrogen (N-2) reduction to ammonia in the Haber-Bosch synthesis is essential for producing fertilizers and, consequently, food. Methods wherein the energy for nitrogen activation is supplied by light could provide more sustainable alternatives to existing ones. The combination of a photosensitizer and a lanthanide catalyst is reported for an effective >2e(-) reduction of N-2 in what is the first transition-metal-free molecular photocatalyst for ammonia synthesis. The lanthanide is Earth-abundant Sm. The reaction proceeds at ambient pressure and temperature, with high turnover numbers (up to 98), with visible light irradiation in aqueous solvent mixtures and even pure water, and it uses an environmentally benign non-metallic sacrificial reductant. Nitrite and nitrate were also efficiently reduced to ammonia. Thus, the first photocatalytic co-reduction of nitrite and bicarbonate to urea using an Sm-based photocatalyst was achieved.

Switchable self-driven photoelectrochemical (PEC) devices are developed to boost H2O2 or electricity generation under visible-light illumination, in which p-n type carbon quantum dots (N-CQDs) is applied as conceptually-new "semiconductor electrolytes". The N-CQDs contains N-dopants, and both negatively- and positively-charged surface groups. This allows N-CQDs to act as the electrolyte and to interact with both a BiVO4 photoanode and a Cu2O photocathode. In a two-compartment cell with a separating membrane, N-CQDs can dynamically form p-n heterojunctions with the photoanode or the photocathode, facilitating charge separation. In this setup, the fine-tuned electronic structure of N-CQDs promotes the two-electron reactions with water or O2 to produce H2O2, achieving a rate of 28 µm min-1 and Faradic efficiency exceeding 80%. Switching into a one-compartment cell, N-CQDs promotes four-electron charge transfer and stabilizes the photoelectrodes, giving electricity output for over 120 h. This control over electron transfer, selectivity, and durability cannot be achieved using traditional electrolytes.

Molecules capable of reversibly transitioning between istinct states in response to multiple stimuli are highly sought after for responsive materials, enabling precise control over electronic structure at the molecular level. While overcrowded alkene (OCA) diradicaloids have shown promise in this context, research has largely centered on carbon-based systems, leaving main-group alternatives underexplored. Herein, we present the synthesis of an air stable, phosphaalkene substituted hybrid OCA diradicaloid, obtained by replacing one exocyclic C=C bond of an anthraquinodimethane core with a low-valent phosphaalkene unit (–C=P–Mes*, Mes*= 2,4,6-tri-tert butylphenyl) and appending a fluorenyl group at the opposite terminus. This unique molecular framework enables distinct responses to external stimuli, as demonstrated by comprehensive spectroscopic analysis and supported by theoretical studies. The molecule undergoes a temperature-induced, reversible conformational change from a folded quinoidal to a twisted diradicaloid state via rotation of the fluorenyl unit about the central overcrowded alkene bond. Furthermore, reversible Lewis acid–base interactions at the phosphorus center dynamically modulate the diradical character, illustrating a rare example of chemical control in a main-group-based OCA diradicaloid. These findings open new avenues for the design of main-group diradicaloids with multi-stimulus responsiveness.

Photocatalytic conversion of biomass-derived compounds into valuable chemicals represents an important advancement for solar-energy conversion. However, conventional semiconductor photocatalysts, composed of multiple elements, exhibit nonuniform catalytic surfaces, complicating catalyst design and mechanistic understanding. Here, we present single-element semiconductors, red phosphorus (RP), to facilitate visible-light-driven Diels-Alder transformations of biomass-derived compounds into high-value products in moderate to good yields. The electron-rich phosphorus atoms effectively adsorb p-toluquinone and activate C-H bonds, leading to the formation of a cationic intermediate via photogenerated holes that promote Diels-Alder electronic matching with a diene into a cationic cyclized adduct. Accompanied by an O2-mediated process, wherein O2 accepts conduction-band electrons and transfers them to the cationic cyclized adduct, the D-A transformation is accomplished without requiring any sacrificial agents. This approach operates under milder and greener conditions, advancing the biomass conversion and highlighting RP's potential in organic synthesis. Additionally, the single-element photocatalyst allows for valuable insights into mechanistic studies.

Constructing aggregation-resistant, full-Quantum Dot (QD)-based S-scheme heterostructures is critical yet challenging for the enhanced photocatalysis. Herein, a charge-directed and defect-induced strategy is presented to fabricate a novel full QD-based heterostructure CdS&CQD and its photocatalytic feature. The CdS&CQD is assembled from a negatively-charged and sulfur-vacancy-rich CdS QD, and a both positively-charged-groups and thiophene-moieties functionalized carbon-quantum-dot (CQD). Electrostatic interaction ensures the close contact between CdS and CQD, suppressing the homo-QD aggregation. Assisted by thiophene groups on CQD and sulfur-vacancies on CdS, they act as complementary "jigsaw puzzle" motifs, guiding the formation of a chemically bonded Cd-S interface. This process results in a colloidally stable full-QD-based CdS&CQD with the maximal active site exposure. The atomic-level connectivity in CdS&CQD established a robust internal electric field, driving S-scheme charge transfer with long-lived excitons and enhanced redox capacity for the photocatalyst. Consequently, CdS&CQD efficiently activates the inert biomass-derived furfural and CO2, enabling synergistic furfural aldol-condensation with acetone to yield a high-value-added product, integrated with the selective CO2-to-CO reduction. CdS&CQD also displays recycling stability as well as the activity under outdoor sunlight irradiation. This work provides fundamental significance for designing and constructing full-QDs-based heterostructures with tailored photocatalytic redox-capabilities.

The reduction of stable trivalent lanthanide species (Ln(III)) by the excited states of organic chromophores is the basis of photocatalytic divalent lanthanide-mediated reduction reactions. While indirect evidence of the photochemical formation of the reactive Ln(II) species is abundant, direct spectroscopic evidence of their presence is scarce. Here, nine chromophores with absorptions covering the near UV and visible ranges were systematically investigated in the presence of Ln(III) ions to evaluate their ability to reduce Eu(III) upon excitation with visible light to the catalytically active Eu(II) species. Irradiated mixtures of Eu(III) and the chromophores were characterized using UV-vis absorption and emission and EPR spectroscopy. Several of the chromophore-Eu(III) combinations were competent photocatalysts in the presence of N,N-diisopropylethylamine or Zn terminal reductants. These results demonstrate that a variety of visible-absorbing chromophores can efficiently generate reactive Eu(II) from Eu(III) to catalyze Ln(II)-mediated reduction reactions.

Industrial dinitrogen reduction to ammonia in the Haber-Bosch synthesis is essential for the production of fertilizers, and consequently, of food. This process accounts for up to 2% of global energy use. Methods wherein the energy for nitrogen activation is supplied by light could provide more sustainable alternatives to existing ones. The first transition-metal free molecular photocatalyst for the reduction of dinitrogen to ammonia is reported. The catalyst is based on Earth-abundant Sm. The reaction proceeds at ambient pressure and temperature with high turnover numbers (up to 70) with visible light irradiation in aqueous solvent mixtures and even pure water, and uses an environmentally benign non-metallic sacrificial reductant. Nitrite and nitrate were also efficiently reduced to ammonia. The first photocatalytic co-reduction of nitrite and bicarbonate to urea using a Sm-based photocatalyst was achieved.

The stepwise reduction of the highly contorted truxene‐based triphosphaalkene 1 using KC8 led to the isolation of mono‐, di‐and tri‐anionic species. The solid‐state molecular structures of mono‐ and diradical anionic species were elucidated by single crystal X‐ray diffractions, revealing elongated P‐C bonds and a pronounced “indene” aromatization compared to the parent system. All three radical species displayed distinct Electron Paramagnetic Resonance (EPR) spectra, providing compelling evidence for the open‐shell electronic configuration of both the diradical and triradical species—an observation unprecedented in any previously reported phosphorous‐based anionic polyradicals. Mulliken spin density calculations revealed a dominant localization of radical spin on a single phosphorous atom in the monoanion. In the dianion, spin localization is observed on two phosphorous atoms (~34% each), with a minor contribution from the third phosphorous (0.13%), while the trianion demonstrates a uniform distribution of spin density (~30%) across each phosphorous atom.

Commercially available coumarin 343 in combination with reducible Sm(III) ions catalyzed divalent lanthanide-mediated C═O, C-halogen, P-Cl, and N═N reductions at ambient temperature in aqueous solvent mixtures. The catalyst absorbs visible light efficiently. The active divalent species is formed by photoinduced electron transfer from coumarin 343 to the stable trivalent precursor, and the coumarin could be regenerated by strictly 1 equiv of ascorbic acid.

Thiele's Hydrocarbons (THs) featuring a 9,10-anthrylene core with switchable geometric and electronic configurations offer exciting possibilities in advanced functional materials. Despite significant advances in main group-based diradicaloids in contemporary chemistry, main group THs containing an anthrylene cores have remained elusive, primarily due to the lack of straightforward synthetic strategies and the inherent high reactivity of these species. In this study, we utilize an anthracene-based phosphine synthon to demonstrate, for the first time, a facile and high-yielding synthetic strategy for robust P-functionalized overcrowded ethylenes (OCEs) within the TH family. These OCEs feature a non-symmetric environment, incorporating (thio) xanthyl and phosphaalkene termini. We systematically probe the electronic structures of these derivatives to illustrate the impact of the isolobal phosphaalkene motif on the quinoidal/diradicaloid character. Notably, the compounds exhibit dynamic redox behavior, leading to orthogonally twisted conformational changes upon oxidation, with a kinetically locked redox-couple.

Divalent lanthanide (Ln) compounds are excellent reducing agents with unique reactivity profiles. These reagents are typically used in superstoichiometric amounts, often in combination with harmful additives. Reactions catalytic in Ln(II) reagents that retain the reactivity and selectivity of the stoichiometric transformations are currently lacking due to the absence of effective and selective methods to form reactive Ln(II) species from stable precursors. Here, active Ln(II) is generated from a Ln(III) precursor through reduction by a photoexcited coumarin or carbostyril chromophore, which, in turn, is regenerated by a sacrificial reductant. The reductant can be metallic (Zn) or organic (amines) and can be used in strictly stoichiometric amounts. A broad range of reactions, including C-halogen, C═C, C═X (X = O, N), P═O, and N═N reductions, as well as C-C, C-X (X = N, S, P), and N-N couplings were readily carried out in yields and selectivities comparable to or better than those afforded by the analogous stoichiometric transformations. The reaction outcomes could be altered by changing the ligand or the lanthanide or through the addition of environmentally benign additives (e.g., water). EPR spectroscopy supported the formation of both Ln(II) and oxidized chromophore intermediates. Taken together, these results establish photochemical Ln(II) generation as a powerful strategy for rendering Ln(II)-mediated reactions catalytic.

The design of molecular water oxidation catalysts (WOCs) requires a rational approach that considers the intermediate steps of the catalytic cycle, including water binding, deprotonation, storage of oxidizing equivalents, O-O bond formation, and O2 release. We investigated several of these properties for a series of base metal complexes (M = Mn, Fe, Co, Ni) bearing two variants of a pentapyridyl ligand framework, of which some were reported previously to be active WOCs. We found that only [Fe(Py5OMe)Cl]+ (Py5OMe = pyridine-2,6-diylbis[di-(pyridin-2-yl)methoxymethane]) showed an appreciable catalytic activity with a turnover number (TON) = 130 in light-driven experiments using the [Ru(bpy)3]2+/S2O82- system at pH 8.0, but that activity is demonstrated to arise from the rapid degradation in the buffered solution leading to the formation of catalytically active amorphous iron oxide/hydroxide (FeOOH), which subsequently lost the catalytic activity by forming more extensive and structured FeOOH species. The detailed analysis of the redox and water-binding properties employing electrochemistry, X-ray absorption spectroscopy (XAS), UV-vis spectroscopy, and density-functional theory (DFT) showed that all complexes were able to undergo the MIII/MII oxidation, but none was able to yield a detectable amount of a MIV state in our potential window (up to +2 V vs SHE). This inability was traced to (i) the preference for binding Cl- or acetonitrile instead of water-derived species in the apical position, which excludes redox leveling via proton coupled electron transfer, and (ii) the lack of sigma donor ligands that would stabilize oxidation states beyond MIII. On that basis, design features for next-generation molecular WOCs are suggested.

Cobalt polypyridyl complexes efficiently catalyze hydrogen evolution in aqueous media and exhibit high stability under reducing conditions. Their stability and activity can be tuned through electronic and steric considerations, but the rationalization of these effects requires detailed mechanistic understanding. As an example, tetradentate ligands with two non-permanently occupied coordination sites show higher activity with these sites in cis compared to trans configuration. Here reaction mechanisms of the Co-polypyridyl complex [Co II (bpma)Cl 2 ] (bpma = bipyridinylmethyl-pyridinylmethyl-methyl-amine) have been studied using hybrid density-functional theory. This complex has two exchangeable cis sites, and provides a flexible ligand environment with both pyridyl and amine coordination. Two main pathways with low barriers are found. One pathway, which includes both open sites, is hydrogen evolution from a Co II -H intermediate with a water ligand as the proton donor. In the second pathway H–H bond formation occurs between the hydride and the protonated bpma ligand, with one open site acting as a spectator. The two pathways have similar barriers at higher pH, while the latter becomes more dominant at lower pH. The calculations consider a large number of interconnected variables; protonation sites, isomers, spin multiplicities, and the identities of the open binding sites, as well as their combinations, thus exploring many simultaneous dimensions within each pathway. The results highlight the effects of having two open cis-coordination sites and how their relative binding affinities change during the reaction pathway. They also illustrate why Co II -H intermediates are more active than Co III -H ones, and why pyridyl protonation gives lower reaction barriers than amine protonation.

Solar conversion of water into the storable energy carrier H2 can be achieved through photoelectrochemical water splitting using light adsorbing anodes and cathodes bearing O2 and H2 evolving catalysts, respectively. Herein a novel photocathode nanohybrid system is reported. This photocathode consists of a dye-sensitized p-type nickel oxide (NiO) with a perylene-based chromophore (PCA) and a tetra-adamantane modified cobaloxime reduction catalyst (Co) that photo-reduces aqueous protons to H2. An original supramolecular approach was employed, using β-cyclodextrin functionalized gold nanoparticles (β-CD-AuNPs) to link the alkane chain of the PCA dye to the adamantane moieties of the cobaloxime catalyst (Co). This new architecture was investigated by photoelectrochemical measurements and via femtosecond-transient absorption spectroscopy. The results show that irradiation of the complete NiO|PCA|β-CD-AuNPs|Co electrode leads to ultrafast hole injection into NiO (π = 3 ps) from the excited dye, followed by rapid reduction of the catalyst, and finally H2 evolution.

Mesoporous NiO photocathodes containing the push-pull dye PB6 and alkyl-derivatized cobaloxime catalysts were prepared using surface amide couplings and analyzed for photocatalytic proton reduction catalysis. The length of the alkyl linker used to derivatize the cobalt catalysts was found to correlate to the photocurrent with the highest photocurrent observed using shorter alkyl linkers but the lowest one for samples without linker. The alkyl linkers were also helpful in slowing dye-NiO charge recombination. Photoelectrochemical measurements and femtosecond transient absorption spectroscopic measurements suggested electron transfer to the surfaceimmobilized catalysts occurred; however, H-2 evolution was not observed. Based on UV-vis, X-ray fluorescence spectroscopy (XRF), and X-ray photoelectron spectroscopy (XPS) measurements, the cobalt catalyst appeared to be limiting the photocathode performance mainly via cobalt demetallation from the oxime ligand. This study highlights the need for a deeper understanding of the effect of catalyst molecular design on photocathode performance.

Ferrous chloride complexes [FeIILxCl] commonly attain a high-spin state independently of the supporting ligand(s) and temperature. Herein, we present the first report of a complete spin crossover with T1/2 = 80 K in [FeII(Py5OH)Cl]+ (Py5OH = pyridine-2,6-diylbis[di(pyridin-2-yl)methanol]). Both spin forms of the complex are analyzed by X-ray spectroscopy and DFT calculations.