3 research outputs found
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 [FeFeĀ(Ī¼-pdt)Ā(CO)<sub>6</sub>] (pdt
= propanedithiolate), <b>1</b>, were investigated by UVāvis
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 H<sub>2</sub> generation.
The one-electron-reduced catalyst was obtained transiently by electron
transfer from photogenerated [RuĀ(dmb)<sub>3</sub>]<sup>+</sup> 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 UVāvis
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 (Ī¼<sup>2</sup>,Īŗ<sup>2</sup>-pdt)Ā(Ī¼-H)ĀFe<sub>2</sub> core in the reduced, <b>1<sup>ā</sup></b>, and reduced-protonated states, <b>1H</b>, in contrast
to the FeāS bond cleavage upon the reduction of [FeFeĀ(bdt)Ā(CO)<sub>6</sub>], <b>2</b>, with a benzenedithiolate bridge. The driving-force
dependence of the rate constants for the protonation of <b>1<sup>ā</sup></b> (<i>k</i><sub>pt</sub> = 7.0 Ć
10<sup>5</sup>, 1.3 Ć 10<sup>7</sup>, and 7.0 Ć 10<sup>7</sup> M<sup>ā1</sup> s<sup>ā1</sup> 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 FeāFe bond. The protonation of <b>1<sup>ā</sup></b> is sufficiently fast even with the weaker acids, which excludes
a rate-limiting role in light-driven H<sub>2</sub> formation under
typical conditions
Detection and Identification of Cu<sup>2+</sup> and Hg<sup>2+</sup> 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 oligoĀ(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 Hg<sup>2+</sup> and Cu<sup>2+</sup> than the other tested divalent metal ions including Zn<sup>2+</sup>, Cd<sup>2+</sup>, Co<sup>2+</sup>, and Pb<sup>2+</sup>.
Further measurements of the fluorescence responses of the film towards
Cu<sup>2+</sup> and Hg<sup>2+</sup> 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 Hg<sup>2+</sup> and Cu<sup>2+</sup>. 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 Co<sup>2+</sup> and Ni<sup>2+</sup>
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 trisĀ(<i>p</i>-anisyl)Āamine
mediator into classic trisĀ(bipyridine)Ācobalt-based
electrolytes, demonstrate favorable electron transfer and reduced
energy loss in dye-sensitized solar cells. Here, we have successfully
explored three trisĀ(4-alkoxyphenyl)Āamine 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 trisĀ(bipyridine)Ācobalt-based electrolytes. Solar
cells with power conversion efficiencies of 9.7ā11.0% under
1 sun illumination were manufactured. This corresponds to an efficiency
improvement of up to 50% as compared to solar cells based on pure
trisĀ(bipyridine)Ācobalt-based electrolytes. The photovoltage increases
with increasing steric effects of the trisĀ(4-alkoxyphenyl)Āamine 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