Modulating the Surface Environment of Lead Sulfide Quantum Dots to Manipulate Energy Transfer across the Inorganic–organic Interface

Elucidating the mechanism behind energy transport is essential to improving the efficiency of energy related functions. In our project, we attempt to uncover the nature of energy transfer dynamics between lead sulfide quantum dots (PbS QDs) and surface bound perylene diimide (PDI) molecules. The two species are energetically aligned in such a way that energy can transfer between them even though they absorb in different regions of the light spectrum. Using transient absorption spectroscopy, we selectively excited the PbS QDs and observed how the system relaxes on a femtosecond timescale. We found that PbS QD transfers an excited electron to PDI within 30 picoseconds to create a radical PDI anion. Furthermore, we can make this process faster or slower by adding cinnamate molecules to the QD surface, which serve to move the energy levels of PbS QDs up and down. This means that we can change the energetic alignment between PbS QD and PDI by synthetically modifying the surface’s electronic environment. This realization is significant because it adds an additional degree of control to preparing energy devices. We believe that this will help in guiding future designs to engineer light harvesting materials.