Electrochemical CO2 reduction reaction (CO2RR) catalyzed by molecular earth-abundant metal catalysts is a promising strategy to convert CO2 into value-added products. One recent trend in this field has been focusing on the rational design of catalysts by incorporating redox-active ligands and modifying the secondary coordination sphere (SCS) to achieve efficient and selective CO2RR. Herein, we report a series of Co bis(bipyridine) catalysts featuring various dangling groups, such as pyridine, tertiary amine, or butyl, in the secondary coordination sphere (Co-PyMe, Co-Py, Co-PrN, and Co-Bu). Efficient, selective electrocatalytic CO2RR was achieved by the complexes after the generation of triply reduced intermediate consisting of a Co-I center and a dianionic ligand, producing CO as the major product and trace amount of H-2. Strong correlations with the identity of dangling groups and turnover frequency (TOF) have been observed, in which Co-PyMe displayed the highest TOF (1086 s(-1) in MeCN/H2O). Mechanistic studies indicated that the acceleration of CO2RR with pyridine-functionalized catalysts were derived from the protonation of pyridine dangling groups which participated as weak acids in the H-bonding network with exogenous proton sources, stabilizing CO2-bound intermediates and facilitating proton transfer. In addition, precatalytic CO2 binding and activation at the third reduction (-2.1 V) was revealed by CV and SEC-IR studies. The resultant doubly reduced CO-bound species acted as a trapping state which inhibited CO2RR electrocatalysis. Regeneration of active species was accessed via reductive dissociation of CO at a more negative potential. This study highlights the combined effects of redox-active ligands and pyridine/pyridinium as SCS groups on CO2RR catalysis and provides design principles for future development of CO2RR catalysts utilizing pyridine/pyridiniums as SCS functional groups to fine-tune the catalytic activity.

Abstract Photonic properties in a plasmonic nanocrystal are directly impacted by carrier density, carrier effective mass, and carrier damping behavior. Postprocessing of as-prepared Cd2SnO4 (CTO) by solvothermal annealing is shown to enhance the localized surface plasmon (LSPR) optical quality through a time-dependent LSPR shift and LSPR narrowing. The change in the LSPR is complex but postulated to be driven by surface reconstruction leading to incorporation of Sn, reduction in size, and defect evolution. The changes in the CTO produce a shift to higher frequency for the LSPR and loss of a high energy shoulder with an exponential rate of k ∼ 1.0 h–1. The improved plasmonic quality factor is due to the overall increase in carrier density and loss of the shoulder during solvothermal annealing. During annealing, an increase in the depletion layer width and a decrease in Sn activation in CTO with k ∼ 0.5 h–1 are also observed. Postprocessing of isolated plasmonic metal oxide nanocrystals through solvo-thermal annealing may represent a convenient strategy to enhance LSPR quality factors, providing a pathway to improving photonic properties in this class of materials.

Mesoporous silicon nitride (Si3N4) enables access to chemisorbed group IV organometallics catalysts active for propane dehydrogenation (PDH) compared to the organometallic analogues on mesoporous silica under the same reaction conditions. The series of Si3N4-supported materials are active catalysts, (Zr > Hf > Ti k f = 290, 232, and 162 mol mol(Metal)(-1) h(-1) at 450 degrees C with 2% C3H8 in Ar, respectively) with selectivity above 95%, demonstrating additional examples of Ti and Hf systems for PDH. However, the underlying mechanism of the improved performance relative to oxide supported homologues is not well-understood. Characterization of thermally treated samples (DRIFTS, XAS and SSNMR) and computational modeling of this catalyst series was utilized to differentiate between potential amido- (C-H activation along the M-N bond) and imido- (C-H activation along the M=N bond) mechanisms. Due to remaining mechanistic ambiguity, a Ga analogue was synthesized and evaluated for PDH activity as an indirect probe to experimentally differentiate pathways. An inversion of the oxide/nitride performance trend is observed for the Ga congener which does not form a Ga=N bond, most consistent with different mechanisms dictating the performance of the group IV/Si3N4 catalysts vs Ga/Si3N4.

Electron spin plays a critical role in determining the structure, dynamics, and reactivities of molecular excited states, including multiexciton processes such as singlet fission. These systems exhibit triplet pair states whose excited state dynamics can be widely tuned through molecular engineering. For example, the electronic coupling between covalently linked chromophores can be readily modulated using chemical bridges to control proximity, quantum interference, or resonance effects. However, less is known about how spin coupling interactions are impacted by chromophore architecture, and how this influences triplet pair recombination dynamics. Here, we investigate the role of bridge connectivity and chromophore identity in modulating interchromophore exchange and dipolar coupling interactions for a series of pentacene and tetracene dimers bridged by alternant hydrocarbons (phenylene, naphthalene, anthracene). Using both time-resolved electron paramagnetic resonance and transient absorption spectroscopy, we find that the boundedness and recombination pathways of the triplet pair spins are highly sensitive to molecular architecture and chromophore-specific magnetic dipolar interactions. Notably, nominally ferromagnetic and antiferromagnetic eigenstates result in distinct spin state orderings, consistent with predictions from quantum interference-based graphical models. These findings establish new design principles for tuning spin dynamics in iSF materials, with implications for photonic and quantum information applications.

We demonstrate the validity of our approach to deduce, from the anisotropy of quantum oscillations, the geometry of short-lived radical pair intermediates in photosynthesis. A global fit of a two-dimensional W-band (94 GHz) electron paramagnetic resonance (EPR) experiment provides the same global minimum values for the geometry of the A-side radical pair P700•+A1A•- in photosystem I (PSI) as observed in a previous Q-band (34 GHz) EPR study, yet with a significantly increased convergence rate of 62%. This demonstrates that the global fit yields the correct radical pair geometry even at Q-band frequencies. With this information, we revisit our previous Q-band study of the cofactor arrangement of P865•+QA•-, the stabilized charge-separated state in purple bacterial reaction centers (RCs). Analysis of calculated two-dimensional data sets of P865•+QA•- reveals that the quantum oscillation technique is unaffected by a mirror ambiguity in disordered solids and thus can provide unambiguous solutions for all five Euler angles of the radical pair geometry. This enables us to elucidate the QA•- to QB electron transfer step in purple bacterial photosynthesis, the subject of controversial discussions for more than 25 years. Our results show that this electron transfer step involves a gating mechanism requiring a 60° rotation of the headgroup of QA•- in its binding pocket.

The development of multifunctional solid-state materials is key to advancing lithium-ion batteries with enhanced safety and simplified architectures. Here, we report a scalable, highly efficient (near 100%), solvent-free mechanochemical synthesis of hexagonal boron nitride (hBN) functionalized with lithium oxalate (Li_2C_2O_4), yielding a novel lamellar composite that functions both as a lithium-ion conductor and separator. The high-energy milling process promotes exfoliation of hBN and covalent attachment of oxalate groups at edge and defect sites, forming a brown, nanocrystalline material with uniform lithium distribution. The composite exhibits room-temperature ionic and negligible electronic conductivity, thermal stability at least up to 350 ^∘C, and hosts stable free radicals enabling its use as a spin label. The synthesis produces no byproducts and can be extended towards lithium doping via secondary mechanochemical steps, creating highly doped, chemically stable phases that host additional Li for ionic conduction. These results introduce a new class of lithium-rich, boron nitride-based solids for solid-state batteries, combining ion conduction, mechanical robustness, and thermal resilience in a single material platform.

Selective ethylene oligomerization via oxidative cyclization, forming metallacyclic intermediates, is typically catalyzed by molecular titanium and chromium complexes to produce butenes, hexenes, or octenes, depending on the supporting ligand framework. However, this mechanism requires significant electron density at the metal active site and is not known to be generalizable to other first-row transition metals. In this work, we computationally investigate the electronic modulation of five transition metals (Mn, Fe, Co, Ni, and Cu) supported on titania (TiO2) through reductive lithium intercalation to promote selective oligomerization via oxidative cyclization, using density functional theory (DFT). Our findings predict that Mn/LiTiO2 exhibits high catalytic activity due to the exergonic nature of oxidative cyclization with two ethylene molecules. Additionally, lithium titanate (LiTiO2) supports enhance catalytic performance compared to TiO2. Experimental validation confirms that Mn/LiTiO2 achieves higher conversion rates and improved selectivity toward hexene (C-4:C-6 = 1:2.6). The enhanced activity is attributed to lithiation, which alters the electronic environment around Mn active sites. Mechanistic studies reveal that the formation of a seven-membered ring, a key intermediate for hexene formation, is more favorable on LiTiO2 than TiO2. This work provides the first evidence of Mn catalyzing selective ethylene oligomerization via oxidative cyclization in either homogeneous or heterogeneous catalysis.

Photogenerated spin-correlated radical pairs (SCRPs) are emerging as promising new candidates for Quantum Information Science applications, where they act as electron spin qubit pairs (SQPs). Historically, these pairs have been mostly investigated in natural photosynthesis and in molecular organic donor-(linker)-acceptor systems. Recently, we have shown that these spin pairs can also be observed by time-resolved electron-paramagnetic resonance (EPR) spectroscopy in hybrid inorganic-organic conjugates. The current study builds on recent work (ACS Nano, 2025, 19, 12194-12207), in which we systematically prepared hybrid inorganic-organic molecule systems with tunable geometries that can host SCRPs/SQPs. Here, we demonstrate using pulsed EPR spectroscopy that we can generate, study, and manipulate the spins in these photogenerated SCRPs hosted on highly tailorable inorganic-organic hybrid systems. Microwave pulse-based spin manipulation is the first step toward developing quantum computing and quantum sensing applications with these promising spin-based qubit materials, which can be reversibly photogenerated in highly spin-polarized states at moderate temperatures. An attractive feature of this new class of hybrid materials is that the g-factor of the unpaired electron spin in the ZnO QD (as part of the SCRP/SQP) can be adjusted using the quantum size effect in these QDs, which allows for the selective addressability of each spin in the SCRP using microwave pulses. Furthermore, we also observed a difference between the g-values of the unpaired electron in the ZnO QD in the transient SCRP state and stable photoreduced state. We hypothesize that the unpaired electron in the SCRP is delocalized as a band-like conduction electron, while in the stable photoreduced state, the electron is delocalized in a shallow electron trap state.

We report a novel water-soluble cobalt( ii )-based quinoline complex capable of bifunctional water splitting. The electrocatalytic behaviour towards water reduction and oxidation were studied, and corresponding mechanisms were proposed.

Optically addressable electronic spins in polyatomic molecules are a promising platform for quantum information science, with the potential to enable scalable qubit design and integration through atomistic tunability and nanoscale localization. However, optical state- and site-selection are an open challenge. In this work, we introduce an organo-erbium spin qubit in which narrow (megahertz-scale) optical and spin transitions couple to provide high-resolution access to spin degrees of freedom with telecommunication-frequency light. This spin-photon interface enables demonstration of optical spin polarization and readout that distinguishes between spin states and magnetically inequivalent sites in a molecular crystal. Operation at frequencies compatible with mature photonic and microwave devices provides an opportunity for engineering scalable, integrated molecular spin-optical quantum technologies.

Photosynthetic biohybrid systems (PBSs) offer an eco-friendly approach to transforming solar energy into value-added products by integrating biological entities with inorganic semiconductors. However, the chemical conversion capacity of most PBSs has inherent limitations, as whole-cell bacteria and isolated enzymes require fine-tuning of environmental conditions. Here, we report a new PBS developed by introducing free-standing ceria nanoparticles into the purple membrane (PM) of Halobacterium salinarum archaea, which can unidirectionally transfer charge carriers in response to incident photons, even after separation from living archaea at various conditions. Our microscopy, spectroscopy, and synchrotron X-ray scattering analyses confirm that the electrostatic assembly between ceria and PM creates seamless interfacial contact, thereby enhancing the photocatalytic capacity of ceria. Although the conversion of dinitrogen (N2) to ammonia (NH3) is thermodynamically challenging due to the triple bond in N2 and a series of charge-transfer reactions, our PM-ceria (PMC) hybrid nanoparticle efficiently produces NH3 by reducing N2 using solar energy even under atmospheric pressure and room temperature while simultaneously converting glycerol into value-added derivatives. Additionally, our PMC nanoparticle involves neither toxic/precious metals nor bioengineering processes to achieve enhanced photocatalytic N2-to-NH3 conversion. This study sheds light on the new aspect of PBSs by employing PM to potentially resolve the global energy and environmental challenges posed by the conventional Haber-Bosch process.

Photosynthetic reaction center proteins (RCs) provide ideal model systems for studying quantum entanglement between multiple spins, a quantum mechanical phenomenon wherein the properties of the entangled particles become inherently correlated. Following light-generated sequential electron transfer, RCs generate spin-correlated radical pairs (SCRPs), also referred to as entangled spin qubit (radical) pairs (SQPs). Understanding and controlling coherence mechanisms in SCRP/SQPs is important for realizing practical uses of electron spin qubits in quantum sensing applications. The bacterial RC (bRC) provides an experimental system for exploring quantum effects in the SCRP P865+ QA-, where P865, a special pair of bacteriochlorophylls, is the primary donor, and QA is the primary quinone acceptor. In this study, we focus on understanding how local molecular environments and isotopic substitution, particularly deuteration, influence spin coherence times (TM). Using high-frequency electron paramagnetic resonance (EPR) spectroscopy, we observed that the local environment surrounding P865 and QA plays a significant role in determining TM. Our findings show that while deuteration led to a modest increase in TM, particularly at low temperatures, but the effect was substantially smaller than predicted by classical nuclear spin diffusion alone. This result is in contrast to our previous study of the photosystem I (PSI) RC, where no increase in TM was observed upon deuteration. Theoretical modeling identified several methyl groups at key distances from the spin centers of both bRC and PSI, and methyl group tunneling at low temperatures has been previously suggested as a mechanism for enhanced spin decoherence. Additionally, our study revealed a strong dependence of spin coherence on the orientation of the external magnetic field, highlighting the influence of the protein microenvironment on spin dynamics. These results offer new insights for optimizing coherence times in quantum system design for quantum information science and sensing applications.

Organic molecules and quantum dots (QDs) have both shown promise as materials that can host quantum bits (qubits). This is in part because of their synthetic tunability. The current work employs a combination of both materials to demonstrate a series of tunable quantum dot-organic molecule conjugates that can both host photogenerated spin-based qubit pairs (SQPs) and sensitize molecular triplet states. The photogenerated qubit pairs, composed of a spin-correlated radical pair (SCRP), are particularly intriguing since they can be initialized in well-defined, nonthermally populated, quantum states. Additionally, the radical pair enables charge recombination to a polarized molecular triplet state, also in a well-defined quantum state. The materials underlying this system are an organic molecular chromophore and electron donor, 9,10-bis(phenylethynyl)anthracene, and a quantum dot acceptor composed of ZnO. We prepare a series of quantum dot-molecule conjugates that possess variable quantum dot size and two different linker lengths connecting the two moieties. Optical spectroscopy revealed that the QD-molecule conjugates undergo photoexcited charge separation to generate long-lived charge-separated radical pairs. The resulting spin states are probed using light-induced time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy, revealing the presence of singlet-generated SCRPs and molecular triplet states. Notably, the EPR spectra of the radical pairs are dependent on the geometry of this highly tunable system. The g value of the ZnO QD anion is size tunable, and the line widths are influenced by radical pair separation. Overall, this work demonstrates the power of synthetic tunability in adjusting the spin specific addressability, satisfying a key requirement of functional qubit systems.

Harnessing water as a sustainable electron source for artificial photosynthesis remains a significant challenge. This work presents Alice-MOF-1, a novel zirconium metal-organic framework (MOF) incorporating hexatopic ligands with a perchlorinated hexa-peri-hexabenzocoronene (HBC) core, as a photocatalyst for CO2 reduction using water as the terminal electron donor. Contortion of the ligand, induced by edge chlorination, minimizes π-stacking and enhances solubility, enabling direct MOF synthesis. The controlled arrangement of chromophores within Alice-MOF-1 is crucial for enabling the complex multielectron redox reactions. The unique ligand architecture within the MOF promotes symmetry-breaking charge transfer (SBCT), a mechanism observed in natural photosynthesis, leading to efficient charge separation with minimal energy loss. Femtosecond transient absorption spectroscopy and time-resolved electron paramagnetic resonance spectroscopy (EPR) confirm the formation of long-lived radical ions, providing direct evidence for efficient SBCT and negligible charge recombination. These findings demonstrate the power of MOF-based chromophore assemblies to mimic nature's light-harvesting strategies for sustainable energy conversion.

To unlock the potential of molecular engineering for practical quantum sensing and computing, it is essential to create and control pure magnetic states in molecular systems. Singlet fission (SF) in organic materials offers a promising approach by generating pairs of triplet excited states from photoexcited singlets. In this work, we investigate SF in a polymer with strategically positioned tetracene pendant groups along a polynorbornene backbone and its oligomeric counterparts, facilitating intrapolymer through-space coupling. Using continuous-wave and pulsed time-resolved electron paramagnetic resonance (EPR) spectroscopy, we elucidate the spin dynamics and identify key intermediates, including the quintet state, that emerge during SF. Our findings reveal that exciton translational motion along the pendant groups enhances the dissociation of triplet pairs, with oligomer length playing a critical role in modulating spin state interconversion and exciton transport. Our results provide key insights into the SF mechanism in polymeric materials and highlight the role of oligomer length in modulating spin state interconversion and exciton transport. This work advances our understanding of SF in polymers, paving the way for their application in quantum information science and energy conversion technologies.

Conjugates between molecules and quantum dots (QDs) have been explored for a range of potential applications from photocatalysis and photovoltaics to quantum information science technologies. A particularly ubiquitous material in many of these applications are ZnO QDs since they can accept and transport electrons and can also act as hosts for unique spin states. Conjugates between molecular light absorbers and ZnO QDs have been explored for decades as components in dye-sensitized solar cells. Recently, these materials have also attracted interest for their ability to produce spin-polarized states upon photoexcitation. The current paper employs a series of light absorbing perylene molecules with different ZnO QD sizes to explore key features of these QD-molecule conjugates: (1) chemical interactions, (2) charge dynamics, and (3) spin polarization. The chemical interactions between the molecules and QDs are determined with binding equilibria and reveal dramatic impact of ligand size. The charge transfer dynamics from photoexcited perylenes to ZnO QDs were found to depend exponentially on the linker length. Finally, time-resolved electron paramagnetic resonance experiments reveal that these conjugates generate spin-polarized states in the form of radical pairs and triplets. These spin states hold promise as potential qubits and also offer an avenue to efficiently sensitize molecular triplets.

Robust spin-photon interfaces with optical transitions in the telecommunication band are essential for quantum networking technologies. Erbium (Er) ions are the ideal candidate with environmentally protected transitions in telecom-C band. Finding the right technologically compatible host material to enable long-lived spins remains a major hurdle. We introduce a new platform based on Er ions in cerium dioxide (CeO2) as a nearly-zero nuclear spin environment (0.04%) epitaxially grown on silicon, offering silicon compatibility for opto-electrical devices. Our studies focus on Er3+ ions and show a narrow homogeneous linewidth of 440 kHz with an optical coherence time of 0.72 mu s at 3.6 K. The reduced nuclear spin noise enables a slow spin-lattice relaxation with a spin relaxation time up to 2.5 ms and an electron spin coherence time of 0.66 mu s (in the isolated ion limit) at 3.6 K. These findings highlight the potential of Er3+:CeO2 platform for quantum networks applications.

Microsecond coherence times are predicted in spin dynamics calculations of a donor–acceptor electron spin pair P+A1A− created upon light excitation of photosystem I (PSI). The effects of nuclear spin diffusion (NSD) due to the anisotropic protein environment on the predicted coherence times TM are studied. Closely positioned pairs and triples of protons located 5–8 Å from the electron spin are shown to largely control TM. Knowledge of the crystal structure of PSI allows for spin dynamics calculations where specific cofactors and amino acid residues are removed or replaced and the identification of anisotropic environmental features controlling electronic decoherence. Finally, we show that NSD alone cannot explain the >3× shorter experimentally observed coherence times and suggest that methyl groups at key protein sites may explain this discrepancy.

In this work, supported organochromium ethylene polymerization catalysts have been tuned to mediate ethylene oligomerization via surface lithiation, which provides a generalizable protocol to control stereoelectronics and redox states of surface organometallic active sites. The homoleptic chromium(IV) alkyl complex Cr(CH2SiMe3)(4) was grafted on high-surface-area anatase titania (TiO2) nanoparticles as well as on silica to produce Cr/TiO2 and Cr/SiO2 , respectively. Treatment of these materials with excess n-butyllithium led to the reduced chromium complexes Cr/Li-x TiO2 and Cr/Li/SiO2, each of which still retains one hydrocarbyl ligand on chromium. A set of heterogeneous complexes were studied by electron paramagnetic resonance and X-ray absorption spectroscopy, which indicate a reduction in the oxidation state of the major chromium species to CrII upon lithiation. Cr/Li-x TiO2 converts ethylene to hexenes with a high selectivity (>80%), which was persistent over 10 days at 80 degrees C, achieving >950 turnovers. The exclusive formation of C-4 and C-6 olefins, preferring the trimerization product, without a statistical (Flory-Schulz) distribution is characteristic of the oxidative cyclization oligomerization mechanism rather than the traditional Cossee-Arlman mechanism, whereas Cr/Li/SiO2 produced a mixture of trimerization and polymerization products, suggesting site heterogeneity in the silica-based material. On the other hand, the unreduced chromium(IV) materials as well as low lithium-containing Cr/Li-x TiO2 (x < 0.16) exclusively produced ultrahigh molecular weight polyethylene, determined by differential scanning calorimetry and gel permeation chromatography analysis, likely formed via a linear-insertion mechanism, with a crossover from the polymerization to oligomerization regime observed at similar to 16% Li intercalation.

Photosynthetic light-dependent reactions occur in thylakoid membranes where embedded proteins capture light energy and convert it to chemical energy in the form of ATP and NADPH for use in carbon fixation. One of these integral membrane proteins is Photosystem I (PSI). PSI catalyzes light-driven transmembrane electron transfer from plastocyanin (Pc) to oxidized ferredoxin (Fd). Electrons from reduced Fd are used by the enzyme ferredoxin-NADP + reductase (FNR) for the reduction of NADP + to NADPH. Fd and Pc are both small soluble proteins whereas the larger FNR enzyme is associated with the membrane. To investigate electron shuttling between these diffusible and embedded proteins, thylakoid photoreduction of NADP + was studied. As isolated, both spinach and cyanobacterial thylakoids generate NADPH upon illumination without extraneous addition of Fd. These findings indicate that isolated thylakoids either (i) retain a “pool” of Fd which diffuses between PSI and membrane bound FNR or (ii) that a fraction of PSI is associated with Fd, with the membrane environment facilitating PSI-Fd-FNR interactions which enable multiple turnovers of the complex with a single Fd. To explore the functional association of Fd with PSI in thylakoids, electron paramagnetic resonance (EPR) spectroscopic methodologies were developed to distinguish the signals for the reduced Fe-S clusters of PSI and Fd. Temperature-dependent EPR studies show that the EPR signals of the terminal [4Fe-4S] cluster of PSI can be distinguished from the [2Fe-2S] cluster of Fd at > 30 K. At 50 K, the cw X-band EPR spectra of cyanobacterial and spinach thylakoids reduced with dithionite exhibit EPR signals of a [2Fe-2S] cluster with g-values g x = 2.05, g y = 1.96, and g z = 1.89, confirming that Fd is present in thylakoid preparations capable of NADP + photoreduction. Quantitation of the EPR signals of P 700 + and dithionite reduced Fd reveal that Fd is present at a ratio of ~ 1 Fd per PSI monomer in both spinach and cyanobacterial thylakoids. Light-driven electron transfer from PSI to Fd in thylakoids confirms Fd is functionally associated (< 0.4 Fd/PSI) with the acceptor end of PSI in isolated cyanobacterial thylakoids. These EPR experiments provide a benchmark for future spectroscopic characterization of Fd interactions involved in multistep relay of electrons following PSI charge separation in the context of photosynthetic thylakoid microenvironments.