Nicolás Arisnabarreta

Photonic synaptic electrocatalysts encode catalytic activity as a writable, retainable state under optical stimulation, enabling history‐dependent performance modulation with potential relevance to scenarios such as intermittent solar illumination and artificial metabolic learning systems. However, most photo‐assisted electrocatalysts are stateless, showing only transient activity enhancement under illumination that vanishes once the light is removed. Here, we establish a photonic synaptic electrocatalyst based on a bimetallic covalent organic framework (Co–Ni─COF), in which optical stimulation writes synaptic information into the catalytic state, and oxygen evolution serves as a stringent functional readout. During electrochemical reactions, Co─Ni─COF shows strong photonic synaptic behavior, featuring excitatory postsynaptic current responses, tunable synaptic plasticity, transitions from short‐term to long‐term plasticity, learning–forgetting–relearning behavior, and long‐term memory retention. Mechanistic investigations reveal that this light‐written and retained state originates from strengthened electronic coupling between Co and Ni centers, promoted charge delocalization and intermetallic charge transfer, and the accumulation of metastable Co(III) active species together with key oxygenated intermediates (*OOH, *OO). Notably, a substantial fraction of enhanced catalytic activity is preserved for hours in the dark, maintaining ∼127% higher than the initial state after 3 h, highlighting its potential for efficient energy conversion under intermittent solar illumination.

Photonic synaptic electrocatalysts encode catalytic activity as a writable, retainable state under optical stimulation, enabling history‐dependent performance modulation with potential relevance to scenarios such as intermittent solar illumination and artificial metabolic learning systems. However, most photo‐assisted electrocatalysts are stateless, showing only transient activity enhancement under illumination that vanishes once the light is removed. Here, we establish a photonic synaptic electrocatalyst based on a bimetallic covalent organic framework (Co–Ni─COF), in which optical stimulation writes synaptic information into the catalytic state, and oxygen evolution serves as a stringent functional readout. During electrochemical reactions, Co─Ni─COF shows strong photonic synaptic behavior, featuring excitatory postsynaptic current responses, tunable synaptic plasticity, transitions from short‐term to long‐term plasticity, learning–forgetting–relearning behavior, and long‐term memory retention. Mechanistic investigations reveal that this light‐written and retained state originates from strengthened electronic coupling between Co and Ni centers, promoted charge delocalization and intermetallic charge transfer, and the accumulation of metastable Co(III) active species together with key oxygenated intermediates (*OOH, *OO). Notably, a substantial fraction of enhanced catalytic activity is preserved for hours in the dark, maintaining ∼127% higher than the initial state after 3 h, highlighting its potential for efficient energy conversion under intermittent solar illumination.

While molecular electrocatalysis for CO ₂ reduction has advanced significantly, a key challenge persists in accurately defining the active site distribution, surface density, and structural organization of heterogenized catalysts at electrode interfaces. In this study, we address this gap by employing self‐assembled monolayers of physisorbed metal porphyrins (Fe and Cu) on graphite electrodes as structurally well‐defined model systems for the electrochemical CO ₂ reduction reaction (CO ₂ RR). High‐resolution scanning tunneling microscopy (STM) revealed crystalline monolayers with uniform active site distribution, offering periodicities of ∼1.5 nm. These monolayers exhibit moderate Faradaic efficiencies (FEs) for CO production, with Fe porphyrin outperforming its Cu analogue. Isotopic labeling experiments were employed to confirm that the product CO originates from added CO ₂ . Bicomponent monolayers comprising Fe porphyrin and catalytically inactive free‐base porphyrin were fabricated to investigate composition–activity relationships. STM imaging enabled direct, quantitative assessment of surface composition, and subsequent CO ₂ RR measurements revealed a systematic decrease in FE with increasing coverage of the catalytically inactive component. These findings demonstrate the utility of molecularly ordered porphyrin monolayers as a powerful platform for probing structure–activity relationships in electrocatalytic CO ₂ reduction with exceptional spatial and compositional precision.

Covalent and metal‐organic frameworks (COFs and MOFs) have shown great promise in light‐driven processes mainly due to their ligand‐to‐metal charge‐separation properties, as well as having access to a diverse range of photoactive metalloligands and organic linkers. However, both frameworks present individual drawbacks that can potentially be avoided by combining both systems (metal and covalent) to produce metal‐covalent organic frameworks (MCOFs), exhibiting the advantages of both material types. Yet, due to their poor crystallinity, the understanding of the structure‐properties relation of MCOFs remains unclear. Herein, we report photoactive linkers in the form of a [Ru(tpy) ₂ ] ²⁺ (tpy: 2,2′,6,2″‐terpyridine) complex which covalently binds to a luminescent pyrene core to yield a new, photoactive Schiff‐base MCOF. The structure, thermal, electronic, and optical properties of this novel material have been exhaustively characterized by a wide range of microscopy, spectroscopic, and computational methods. This combined experimental and computational work represents a significant step toward the fundamental understanding of the photoactive units within the framework, their hierarchical arrangement and interactions with substrates, which is essential for the future design of efficient photocatalytic materials.

The reversible formation of hydrogen bonds is a ubiquitous mechanism for controlling molecular assembly in biological systems. However, achieving predictable reversibility in artificial two-dimensional (2D) materials remains a significant challenge. Here, we use an external electric field (EEF) at the solid/liquid interface to trigger the switching of H-bond-linked 2D networks using a scanning tunneling microscope. Assisted by density functional theory and molecular dynamics simulations, we systematically vary the molecule-to-molecule interactions, i.e., the hydrogen-bonding strength, as well as the molecule-to-substrate interactions to analyze the EEF switching effect. By tuning the building block's hydrogen-bonding ability (carboxylic acids vs aldehydes) and substrate nature and charge (graphite, graphene/Cu, graphene/SiO₂), we induce or freeze the switching properties and control the final polymorphic output in the 2D network. Our results indicate that the switching ability is not inherent to any particular building block but instead relies on a synergistic combination of the relative adsorbate/adsorbate and absorbate/substrate energetic contributions under surface polarization. Furthermore, we describe the dynamics of the switching mechanism based on the rotation of carboxylic groups and proton exchange, which generate the polarizable species that are influenced by the EEF. This work provides insights into the design and control of reversible molecular assembly in 2D materials, with potential applications in a wide range of fields, including sensors and electronics.

We demonstrated the solution synthesis of curved pyrene-based GNRs bearing cove- and armchair-edges via a one-pot oxidative reaction.