Article pubs.acs.org/JPCC
Ligand-Induced Changes in the Characteristic Size-Dependent Electronic Energies of CdSe Nanocrystals Brian P. Bloom,† Liu-Bin Zhao,†,‡ Yang Wang,† and David H. Waldeck*,† †
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, China
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Ruibin Liu,§ Peng Zhang,§ and David N. Beratan§ §
Department of Chemistry, Duke University, Durham, North Carolina 27708, United States S Supporting Information *
ABSTRACT: This work explores the electronic energy of CdSe nanoparticles as a function of nanoparticle (NP) size and capping ligand. Differential pulse voltammetry was used to determine the valence band edge of CdSe NPs that are capped with three different ligands (aniline, thiophenol, and phenylphosphonic acid), and the experimental values are compared with DFT calculations. These results show how the energy position and the size-dependent behavior of the energy bands of CdSe can be modulated by the chemical nature of the capping ligand. The computations underscore how the nature of the highest lying filled states of the nanoparticle can change with ligand type and how this can explain differences between previously reported sizedependent data on similar systems. The findings show that both the ligand and quantum confinement effects should be accounted for in modeling size-dependent effects for different NP−ligand systems.
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NP,13−15 to affect photophysical properties,16−18 and to modulate the confinement of the exciton.19−21 Over the past decade, a few workers have explored how the capping ligand affects the electronic band energies of CdSe NPs. In 2001, Wang et al. reported that the reduction potential of 7.0 nm TOPO-capped CdSe was less negative (−0.8 eV) than 7.0 nm octanethiol-capped CdSe NP (−1.07 eV).22 Since then, photoemission experiments measuring the VBM were performed on TOPO-capped and pyridine-capped CdSe NPs over a size range of 2.0−4.0 nm and showed how the VBM is shifted by the two different capping ligands on the NP.23 Soreni-Harari et al. studied this phenomenon in greater depth by using differential pulse voltammetry to study the VBM of 4.4 and
