Subpicosecond Photoinduced Hole Transfer from a CdS Quantum Dot to a Molecular Acceptor Bound Through an Exciton-Delocalizing Ligand

Abstract

This paper describes the enhancement of the rate of hole transfer from a photoexcited CdS quantum dot (QD), with radius R = 2.0 nm, to a molecular acceptor, phenothiazine (PTZ), by linking the donor and acceptor through a phenyldithiocarbamate (PTC) linker, which is known to lower the confinement energy of the excitonic hole. Upon adsorption of PTC, the bandgap of the QD decreases due to delocalization of the exciton, primarily the excitonic hole, into interfacial states of mixed QD/PTC character. This delocalization enables hole transfer from the QD to PTZ in <300 fs (within the instrument response of the laser system) when linked by PTC, but not when linked by a benzoate group, which has a similar length and conjugation as PTC but does not delocalize the excitonic hole. Comparison of the two systems was aided by quantification of the surface coverage of benzoate and PTC-linked PTZ by (1)H NMR. This work provides direct spectroscopic evidence of the enhancement of the rate of hole extraction from a colloidal QD through covalent linkage of a hole acceptor through an exciton-delocalizing ligand.

Susceptible Surface Sulfide Regulates Catalytic Activity of CdSe Quantum Dots for Hydrogen Photogeneration

“…As previous reports show that MPA or S 2− mainly work as the hole trap for CdSe QDs, the hole related absorption signal is focused. The faster kinetic decay of the signals of CdSe‐ n S QDs ( n = 25, 75) than that of MPA‐CdSe QDs (Figure d) indicates much more efficient hole transfer process occurred in the CdSe‐25S and CdSe‐75S (Table S1, Supporting Information) . The short lifetime (<3 ps) is highly related to the hole trapping process via surface MPA or S 2− in CdSe QDs.…”

Electrochemical Characterization of CdSe Monolayers Modified with Glycosilated Molecules

“…Cadmium Selenide nanocrystals (CdSe‐NCs) constitute a very interesting class of low dimensional semiconducting materials, because of their unique optical characteristics , which lend themselves in the development of photovoltaic and photocatalic cells or of devices for cancer detection, signal transduction, sensing, etc. . In this respect hybrid systems obtained by the integration of CdSe‐NCs and organic molecules are promising materials because they combine the properties of both components with the advantage of being more flexible and more resistant against oxidative degradation.…”

Quantum Dots Based Photocatalytic Hydrogen Evolution

“…Besides, the strong quantum‐confined effect makes the transport of charge carriers outside the boundary of QDs more easily . Thus, the charge transfer is more efficient in QDs and other quantum‐confined structure like nanorods (quantum rod) and nanoplatelets . Moreover, multiple photons could be absorbed, and multiple excitons could be generated per QD at the same time .…”

“…[20,25,26] Thus, the charge transfer is more efficient in QDs and other quantum-confined structure like nanorods (quantum rod) and nanoplatelets. [20,[27][28][29][30] Moreover, multiple photons could be absorbed, and multiple excitons could be generated per QD at the same time. [11,31] When a hot exciton state is formed by absorbing a photon with hν > 2E g , the hot exciton may cool to the band gap, creating one exciton in the lowest energy state, or undergo multiple exciton generation to create two or more excitons.…”