Colloidal Quantum Dots: Think Outside the (Particle-in-a-)Box

This Perspective discusses recent work on mechanisms by which organic ligands affect the electronic structure and exciton dynamics of colloidal quantum dots (QDs). Much of the work described here uses some combination of steady-state absorption, transient absorption, steady-state photoluminescence, and transient photoluminescence spectroscopies to characterize QD-ligand complexes. Ligands affect the ground-state electronic structure of QDs via mixing of the frontier orbitals at the QD-ligand interface and influence the dynamics of excitonic decay by mediating charge trapping or by participating in charge transfer. This Perspective highlights strategies to address the various forms of structural and chemical heterogeneity of QD ensembles in identifying the mechanisms of these ligand-mediated processes. Finally, four-wave mixing techniques are discussed as promising methods for direct measurement of ligand-mediated nonradiative dissipation of the QD exciton.