Conical Intersections Shed Light on Hot Carrier Cooling in Quantum Dots

TL;DR

This study demonstrates that conical intersections play a key role in hot carrier cooling in quantum dots, with ligand type influencing relaxation dynamics, supported by a model matching experimental vibronic coherence data.

Contribution

The paper extends the conical intersection framework to carboxylate-passivated quantum dots, showing ligand-dependent effects on hot carrier relaxation dynamics.

Findings

Conical intersections are central to hot carrier cooling in various quantum dots.

Ligand type affects electronic and vibrational coupling mechanisms.

Model accurately reproduces vibronic coherence frequencies across different ligands.

Abstract

Experimental observations of vibronic coherences in electronically excited colloidal semiconductor nanocrystals offer a window into the ultrafast dynamics of hot carrier cooling. In previous work, we showed that, in amine-passivated quantum dots (QDs), these coherences arise during relaxation through a cascade of conical intersections between electronically excited states. Here, we demonstrate the generality of this framework by application to QDs with surface-bound carboxylate ligands. A model involving a similar cascade of conical intersections accurately reproduces the frequencies of vibronic coherences observed with broadband multidimensional spectroscopy. The impact of ligands on the relaxation dynamics is attributed to two distinct mechanisms involving either electronic or vibrational coupling between the core and ligands. Compared to the amine-passivated QDs studied previously, the electronic coupling mechanism is less prominent in carboxylate-passivated QDs. Furthermore, comparison of acetate and formate ligands reveals that truncating the ligand alkyl chains alters the relaxation behavior predicted by the model.