Journal
ACS NANO
Volume 10, Issue 6, Pages 6372-6382Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.6b02814
Keywords
CdS quantum dot; hole transfer; exciton delocalization; dithiocarbamate; electronic coupling; transient absorption spectroscopy
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Funding
- National Science Foundation [CHE-1400596, DGE-1324585]
- U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC0000989]
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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 H-1 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.
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