Harnessing Organic Ligand Libraries for First-Principles Inorganic Discovery: Indium Phosphide Quantum Dot Precursor Design Strategies

Indium
phosphide quantum dots (QDs) represent promising replacements
for more toxic QDs, but InP QD production lags behind other QD materials
due to limited understanding of how to tune InP QD growth. We carry
out a first-principles, computational screen of the tuning of In carboxylate
precursor chemistry to alter the kinetics of elementary steps in InP
QD growth. We employ a large database normally used for discovery
of therapeutic drug-like molecules to discover design rules for these
inorganic complexes while maintaining realism (i.e., stable, synthetically
accessible substituents) and providing diversity in a 210-molecule
test set. We show the In–O bond cleavage energy, which is tuned
through ligand functionalization, to be a useful proxy for In–P
bond formation energetics in InP QD synthesis. Energy decomposition
analysis on a 32-molecule subset reveals that lower activation energies
correlate to later transition states, due to stabilization from greater
In–P bond formation and more favorable reaction energetics.
Our simulations suggest that altering ligand nucleophilicity tunes
the reaction barrier over a 10 kcal/mol range, providing the conjugate
acid’s pKa as an experimental handle
to lead to better control of growth conditions and to improve synthesized
InP QD quality. Importantly, these trends hold regardless of phosphorus
precursor chemistries and in the longer chain length ligands typically
used in synthesis.