Abstract
The photophysical properties of Cu-deficient Cu0.2In1Sx quantum dots synthesized through a facile aqueous-based procedure have been investigated. Transient absorption experiments were carried out probing in the UV–vis, near-IR, and mid-IR regions, with the aim to (i) study the photophysical properties of the quantum dots and (ii) monitor kinetics of electron transfer to a molecular catalyst. When pumping sub-bandgap transitions, negative (bleach) signals were observed that were spectrally and kinetically distinct from those observed with bandgap pump wavelengths. Herein, these distinct contributions are suggested to result from the overlapping bleaching of state filling electrons and trapped holes. Such an interpretation highlights the importance of considering the hole-contributions to the bleach for the proper determination of carrier kinetics in similar systems. A model complex of the [Fe2]-hydrogenase active site was introduced to explore the potential of the quantum dots as photosensitizers for molecular catalysts. The quantum dot photoluminescence was quenched upon catalyst addition, and direct evidence of the singly reduced catalyst was found by transient absorption in the UV–vis and mid-IR. The catalyst accepted reducing equivalents on a subpicosecond time scale upon photoexcitation of the quantum dots, despite no covalent linking chemistry being applied. This implies that charge transfer is not limited by diffusion rates, thus confirming the presence of spontaneous quantum dot and catalyst self-assembly.
Highlights
In recent years, two key challenges have been on the agenda in science, technology, and politics: first, to meet the needs of a rising global energy demand resulting from population growth, the aspiration for equal human prosperity, and the increasing energy requirements of the richer population
From highresolution TEM (HRTEM) line-profile (Figure S1e) and powder X-ray diffraction (PXRD, Figure S1d), the quantum dots (QDs) can be indexed to the chalcopyrite or zinc blende phase of CuInS2 with a Cu:In ratio of ∼1:5 (Cu0.2In1Sx) as determined by inductively coupled plasma (ICP) measurements (Table S1)
The transient spectra revealed overlapping bleaching of bandgap (B1) and sub-bandgap (B2) transitions with major contributions from state filling electrons and holes, respectively. This model strengthens the picture of dual optical transitions present in CIS QDs, where the compositional stoichiometry plays a crucial role in determining the relative weight of the transitions involved
Summary
Two key challenges have been on the agenda in science, technology, and politics: first, to meet the needs of a rising global energy demand resulting from population growth, the aspiration for equal human prosperity, and the increasing energy requirements of the richer population. From the variety of phenomena that nature offers to meet our needs, the direct harnessing of the sun’s energy to form solar fuels could transform the way energy is supplied and contribute to resolve these challenges in a sustainable and renewable manner.[1−5]. In the field of photocatalysis, photons are used as the energy source to facilitate energetically downhill (ΔG < 0) chemical reactions. Nature has given us a blueprint for how the principles of photocatalysis can be extended to drive energetically uphill (ΔG > 0) reactions, allowing the sun’s energy to be stored in chemical bonds for the future use as an energy source. The efficiency of photocatalytic systems is partly dictated by the photosensitizer: its absorption
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