Ultrafast Electron Transfer from Photoexcited CdSe Quantum Dots to Methylviologen

Abstract

The ultrafast charge separation at the quantum dot (QD)/molecular acceptor interface was investigated in terms of acceptor concentration and the size of the QD. Time-resolved experiments revealed that the electron transfer (ET) from the photoexcited QD to the molecular acceptor methylviologen (MV(2+)) occurs on the fs time scale for large acceptor concentrations and that the ET rate is strongly reduced for low concentrations. The increase in the acceptor concentration is accompanied with a growth in the overlap of donor and acceptor wavefunctions, resulting in a faster reaction until the MV(2+) concentration reaches a saturation limit of 0.3-0.4 MV(2+) nm(-2). Moreover, we found significant QD size dependence of the ET reaction, which is explained by a change of the free energy (ΔG).

Recent Progress in Photocatalysis Mediated by Colloidal II‐VI Nanocrystals

“…The shift of band-edge potentials with nanocrystal size and the corresponding change in Δ G for the example of ET from CdSe to MV 2+ are depicted in Figure 2a. The resulting effects on charge-transfer rates have been demonstrated for ET from CdSe QDs to molecular species such as an adsorbed Re–bipyridyl complex,127 adsorbed MV 2+ ,99 and covalently linked thiol-functionalized fullerene 123. The rate of ET to MV 2+ has an exponential dependence on Δ G as predicted by Equation (1) (Figure 2b) 99.…”

“…To understand the factors that control the rates of charge transfer from photoexcited nanocrystals, Marcus theory of ET120,121 is commonly invoked 10,83,85,86,97,99,108,122–124. Within this framework, the rate constant for ET ( k ET ) from an electron donor (D) to an electron acceptor (A) is given by Equation (1):…”

“…When not directly measured,126 nanocrystal redox potentials are most commonly estimated by applying quantum confinement corrections to the bulk band-edge potentials of the materials in question 3,82,99,102,106,108,123. In the materials discussed herein, most of the band-gap shift is allocated to the conduction-band levels because electrons are considerably lighter than holes.…”

“…The resulting effects on charge-transfer rates have been demonstrated for ET from CdSe QDs to molecular species such as an adsorbed Re–bipyridyl complex,127 adsorbed MV 2+ ,99 and covalently linked thiol-functionalized fullerene 123. The rate of ET to MV 2+ has an exponential dependence on Δ G as predicted by Equation (1) (Figure 2b) 99. Likewise, the electron injection rate from CdSe QDs to molecularly linked TiO 2 increased exponentially with decreasing QD size (Figure 3a) 106.…”

Facile Synthesis of Glutathione-capped CdS Quantum Dots as a Fluorescence Sensor for Rapid Detection and Quantification of Paraquat

“…With the aim of contributing to exploiting the advantages of QDs as a fluorescence detection probe, the present work is focused on the development of an analytical application for PA determination in environmental and agricultural samples by measuring the dramatically quenching effect on the fluorescence emission of QDs after direct interaction with PA based on electron transfer (ET). [15][16][17] Based on this phenomenon, a sensitive, simple, rapid and low-cost fluorescence method has been established for detection of PA. Compared with previous studies, this proposal method is more simple and time-saving for PA detection.…”