Supramolecular assembly of urea-tethered benzophenone molecules results in the formation of remarkably persistent triplet radical pairs upon UV irradiation at room temperature, whereas no radicals were observed in solution. The factors that lead to emergent organic radicals are correlated with the microenvironment around the benzophenone carbonyl, types of proximal hydrogens, and the rigid supramolecular network. The absorption spectra of the linear analogues were rationalized using time-dependent density functional theory calculations on the crystal structure and in dimethyl sulfoxide, employing an implicit solvation model to describe structural and electronic solvent effects. Inspection of the natural transition orbitals for the more important excitation bands of the absorption spectra indicates that crystallization of the benzophenone-containing molecules should present a stark contrast in photophysical properties versus that in solution, which was indeed reflected by their quantum efficiencies upon solid-state assembly. Persistent organic radicals have prospective applications ranging from organic light-emitting diode technology to NMR polarizing agents.

Inspired by the proficiency of natural enzymes, mimicking of nanoenvironments for precise substrate preorganisation is a promising strategy in catalyst design. However, artificial examples of enzyme-like activation of H2O molecules for the challenging oxidative water splitting reaction are hardly explored.Here, we introduce a mononuclear Ru(bda) complex (M1, bda: 2,2'-bipyridine-6,6'-dicarboxylate) equipped with a bipyridine-functionalized ligand to preorganize H2O molecules in front of the metal center as in enzymatic clefts. The confined pocket of M1 accelerates chemically driven water oxidation at pH 1 by facilitating a water nucleophilic attack pathway with a remarkable turnover frequency of 140 s −1 that is comparable to the oxygen-evolving complex of photosystem II. Single crystal X-ray analysis of M1 under catalytic conditions allowed the observation of a 7 th H2O ligand directly coordinated to a Ru III center.Via a well-defined hydrogen-bonding network, another H2O substrate is preorganized for the crucial O-O bond formation via nucleophilic attack.

Ac yclic dinuclear ruthenium(bda) (bda:2 ,2'-bipyridine-6,6'-dicarboxylate)c omplex equipped with oligo(ethylene glycol)-functionalized axial calix[4]arenel igandsh as been synthesized for homogenous catalytic water oxidation. This novel Ru(bda) macrocycle showeds ignificantlyi ncreasedc atalytic activity in chemical and photocatalytic water oxidationc ompared to the archetype mononuclear reference [Ru(bda)(pic) 2 ]. Kinetic investigations, including kinetic isotope effect studies, disclosed au nimolecularw ater nucleophilic attack mechanismo ft his novel dinuclear water oxidation catalyst (WOC) under the involvement of the secondc oordination sphere.P hotocatalytic water oxidation with this cyclic dinuclearR uc omplex using [Ru(bpy) 3 ]Cl 2 as a standardp hotosensitizer revealed at urnover frequency of 15.5 s À1 and at urnover number of 460. This so far highest photocatalyticp erformance reported for aR u(bda) complex underlines the potential of this water-solubleW OC for artificial photosynthesis.

Proton-coupled electron-transfer (PCET) processes play a key role in biocatalytic energy conversion and storage, for example, photosynthesis or nitrogen fixation. Here, we report a series of bipyridinecontaining di-to tetranuclear Ru(bda) macrocycles 2 C-4 C (bda: 2,2'-bipyridine-6,6'-dicarboxylate) to promote OÀ O bond formation. In photocatalytic water oxidation under neutral conditions, all complexes 2 C-4 C prevail in a folded conformation that support the water nucleophilic attack (WNA) pathway with remarkable turnover frequencies of up to 15.5 s À 1 per Ru unit respectively. Single-crystal X-ray analysis revealed an increased tendency for intramolecular π-π stacking and preorganization of the proximal bases close to the active centers for the larger macrocycles. H/D kinetic isotope effect studies and electrochemical data demonstrate the key role of the proximal bipyridines as proton acceptors in lowering the activation barrier for the crucial nucleophilic attack of H 2 O in the WNA mechanism.

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