# Dynamic Nanocrystal-Ligand Boundaries: Reversible Photoinduced Ligand Detachment from Quantum Dots in Solution

## TL;DR

This paper shows that light can temporarily remove ligands from quantum dots, increasing surface porosity for charge transfer while maintaining stability.

## Contribution

The study introduces reversible photoinduced ligand detachment as a method to transiently modify quantum dot surface porosity.

## Key findings

- Photoinduced ligand detachment increases porosity of oleic acid-passivated CdSe QDs.
- Lower ligand shell density increases ligand escape probability and duration.
- Multilayer ligand coronas prevent ligand detachment due to a cage effect.

## Abstract

The porosity of ligand shells of colloidal quantum dots
(QDs) can
influence the overall rate and yield of charge transfer processes
occurring at their surfaces. However, the density of ligand shells
on QDs can also influence their colloidal and photochemical stability.
We used time-resolved infrared spectroscopy to show that photoinduced
ligand detachment, the tendency for certain ligands to detach from
QD surfaces when the nanocrystals are promoted to their excitonic
excited states, can be used to transiently enhance the porosity of
oleic acid-passivated CdSe QDs in solution. Furthermore, we synthesized
CdSe QDs with varying ligand shell densities to examine the corresponding
influence that van der Waals interactions among ligands have on the
yield of photoinduced ligand detachment and the time scale on which
ligands return to QD surfaces. We observed that oleic acid ligands
on CdSe QDs with lower shell densities have a higher probability of
escape for longer periods of time. Despite this, oleic acid ligands
on fully passivated CdSe QDs are still able to photodetach, resulting
in a transient increase of their ligand shell porosity. In contrast,
QDs with multilayer ligand coronas exhibit negligible photoinduced
ligand detachment because the outer molecular layers introduce a type
of cage effect, preventing the escape of the interior ligands. Our
findings suggest the intriguing possibility that photoinduced ligand
detachment can be used to transiently decrease the density of ligand
shells of QDs to facilitate charge transfer processes while still
allowing them to be fully passivated between excitation events for
photochemical and colloidal stability.