Acid–Base Mediated Ligand Exchange on Near-Infrared Absorbing, Indium-Based III–V Colloidal Quantum Dots
Jari Leemans, Kim Corinna Dümbgen, Matthias M. Minjauw, Qiang Zhao, A. Vantomme, Ivan Infante, Christophe Detavernier, Zeger Hens
Abstract
Colloidal quantum dots (QDs) made from In-based III–V semiconductors are emerging as a printable infrared material. However, the formulation of infrared inks and the formation of electrically conductive QD coatings is hampered by a limited understanding of the surface chemistry of In-based QDs. In this work, we present a case study on the surface termination of IR active III–V QDs absorbing at 1220 nm that were synthesized by reducing a mixture of indium halides and an aminoarsine by an aminophosphine in oleylamine. We find that this recently established synthesis method yields In(As,P) QDs with minor phosphorus admixing and a surface terminated by a mixture of oleylamine and chloride. Exposing these QDs to protic surface-active compounds RXH, such as fatty acids or alkanethiols, initiates a ligand exchange reaction involving the binding of the conjugate base RX– and the desorption of 1 equiv of alkylammonium chloride. Using density functional theory simulations, we confirm that the formation of the alkylammonium chloride salt can provide the energy needed to drive such acid/base mediated ligand exchange reactions, even for weak organic acids such as alkanethiols. We conclude that the unique surface termination of In(As,P) QDs, consisting of a mixture of L-type and X-type ligands and acid/base mediated ligand exchange, can form a general model for In-based III–V QDs synthesized using indium halides and aminopnictogens.