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摘要
Ru(II)-polybipyridine complexes are efficient oxidizers and charge-transfer agents. Combined with semiconductor quantum dots (QDs) they show promising potential for solar energy conversion. Using density functional theory (DFT) and time-dependent DFT (TD-DFT), we study the ground- and excited-state properties of PbSe and ZnO QDs functionalized by Ru(II)-trisbipyridine derivatives, The calculated binding energies elucidate that the most stable QD-complex structures occur through binding of the complex in a bridging mode, when the carboxylate group of the complex is bound to the two metal ions on the QD surface. However, independent of the attachment and the type and size of the QD, the complex introduces unoccupied molecular orbitals near the edge of the conduction band of the QD, while occupied orbitals localized on Ru(II) are deep inside the QDs%26apos; valence band. Such an energy alignment of the complex%26apos;s and QD%26apos;s orbitals makes the hole transfer from the photoexcited QD to the complex energetically unfavorable but supports a scenario of electron and energy transfer from the photoexcited complex to the QD. For small 1 nm PbSe and ZnO QDs, the lowest absorption peak originates from the complex and is well-separated from the next peak associated with the QD transitions, thus providing well-controlled excitation of either the QD or the complex. For PbSe QDs 2 nm in size and larger, however, the first absorption peak belongs to the QD transitions, while the next peak in the absorption spectra originates from both the QD%26apos;s and the complex%26apos;s transitions. The overlap between complex%26apos;s and QD%26apos;s optical transitions tends to hinder controllable excitation and regulated charge-transfer processes in experimental probes.
- 出版日期2013-9-5
