Session: Physical Chemistry Poster:

Recent focus on assemblies of the quantum dots (QDs) functionalized by various organic and metal-organic dyes is dictated by their promise to serve as a key element for both solar-to-electrical and solar-to-chemical energy conversion processes. In both types of applications, conditions and mechanisms of the charge transfer from the photoexcited QD to the dye or backward play a crucial role in the device performance. Applying non-adiabatic molecular dynamics (NAMD) and the Fewest Switching Surface Hopping (FSSH) methods, we have revealed ultrafast hole transfer (~10 fs) from the CdSe QD to the Ru(II) black dye, following by a slow component (~100 fs) associated with the redistribution of population throughout QD states in the energy range of the initial excitation. As such, our calculations prove the realization of the ultrafast interfacial hole transfer from the photoexcited CdSe QD to the dye, which is rationalized by strong non-adiabatic couplings between the QD surface states and the high frequency vibrations of the isocyanide ligands of the black dye. We also have studied the effect of the complex heterostructures of Janus QDs, where a half of the QD is made from CdSe and another half is from PbSe forming an interface along a specific crystalline direction, which permits more control over the charge transfer processes and the overall efficiency of the energy conversion. We have found that the Pb-enriched (111) crystalline direction of the interface provides a charge-transfer character of lower energy transitions, with an electron more localized on the PbSe surface, while the hole is delocalized over the black dye. Overall, our calculations provide atomistic insights into the surface chemistry of QD-dye composites, which knowledge is needed for controlling charge transfer by means of the QD interface and QD-molecule engineering.

Svetlana Kilina

North Dakota State University

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