Structural and Kinetic Studies of Intermediates of a Biomimetic Diiron Proton-Reduction Catalyst

One-electron reduction and subsequent protonation of a biomimetic proton-reduction catalyst [FeFe­(μ-pdt)­(CO)₆] (pdt = propanedithiolate), <b>1</b>, were investigated by UV–vis and IR spectroscopy on a nano- to microsecond time scale. The study aimed to provide further insight into the proton-reduction cycle of this [FeFe]-hydrogenase model complex, which with its prototypical alkyldithiolate-bridged diiron core is widely employed as a molecular, precious metal-free catalyst for sustainable H₂ generation. The one-electron-reduced catalyst was obtained transiently by electron transfer from photogenerated [Ru­(dmb)₃]⁺ in the absence of proton sources or in the presence of acids (dichloro- or trichloroacetic acid or tosylic acid). The reduced catalyst and its protonation product were observed in real time by UV–vis and IR spectroscopy, leading to their structural characterization and providing kinetic data on the electron and proton transfer reactions. <b>1</b> features an intact (μ²,κ²-pdt)­(μ-H)­Fe₂ core in the reduced, <b>1^–</b>, and reduced-protonated states, <b>1H</b>, in contrast to the Fe–S bond cleavage upon the reduction of [FeFe­(bdt)­(CO)₆], <b>2</b>, with a benzenedithiolate bridge. The driving-force dependence of the rate constants for the protonation of <b>1^–</b> (<i>k</i>_pt = 7.0 × 10⁵, 1.3 × 10⁷, and 7.0 × 10⁷ M^–1 s^–1 for the three acids used in this study) suggests a reorganization energy >1 eV and indicates that hydride complex <b>1H</b> is formed by direct protonation of the Fe–Fe bond. The protonation of <b>1^–</b> is sufficiently fast even with the weaker acids, which excludes a rate-limiting role in light-driven H₂ formation under typical conditions

Detection and Identification of Cu²⁺ and Hg²⁺ Based on the Cross-reactive Fluorescence Responses of a Dansyl-Functionalized Film in Different Solvents

A dansyl-functionalized fluorescent film sensor was specially designed and prepared by assembling dansyl on a glass plate surface via a long flexible spacer containing oligo­(oxyethylene) and amine units. The chemical attachment of dansyl moieties on the surface was verified by contact angle, XPS, and fluorescence measurements. Solvent effect examination revealed that the polarity-sensitivity was retained for the surface-confined dansyl moieties. Fluorescence quenching studies in water declared that the dansyl-functionalized SAM possesses a higher sensitivity towards Hg²⁺ and Cu²⁺ than the other tested divalent metal ions including Zn²⁺, Cd²⁺, Co²⁺, and Pb²⁺. Further measurements of the fluorescence responses of the film towards Cu²⁺ and Hg²⁺ in three solvents including water, acetonitrile, and THF evidenced that the present film exhibits cross-reactive responses to these two metal ions. The combined signals from the three solvents provide a recognition pattern for both metal ions at a certain concentration and realize the identification between Hg²⁺ and Cu²⁺. Moreover, using principle component analysis, this method can be extended to identify metal ions that are hard to detect by the film sensor in water such as Co²⁺ and Ni²⁺

Efficient Dye-Sensitized Solar Cells with Voltages Exceeding 1 V through Exploring Tris(4-alkoxyphenyl)amine Mediators in Combination with the Tris(bipyridine) Cobalt Redox System

Tandem redox electrolytes, prepared by the addition of a tris­(<i>p</i>-anisyl)­amine mediator into classic tris­(bipyridine)­cobalt-based electrolytes, demonstrate favorable electron transfer and reduced energy loss in dye-sensitized solar cells. Here, we have successfully explored three tris­(4-alkoxyphenyl)­amine mediators with bulky molecular structures and generated more effective tandem redox systems. This series of tandem redox electrolytes rendered solar cells with very high photovoltages exceeding 1 V, which approaches the theoretical voltage limit of tris­(bipyridine)­cobalt-based electrolytes. Solar cells with power conversion efficiencies of 9.7–11.0% under 1 sun illumination were manufactured. This corresponds to an efficiency improvement of up to 50% as compared to solar cells based on pure tris­(bipyridine)­cobalt-based electrolytes. The photovoltage increases with increasing steric effects of the tris­(4-alkoxyphenyl)­amine mediators, which is attributed to a retarded recombination kinetics. These results highlight the importance of structural design for optimized charge transfer at the sensitized semiconductor/electrolyte interface and provide insights for the future development of efficient dye-sensitized solar cells