Short-Chain Acids Sustain InAs Colloidal Quantum Dot Growth during Synthesis, Extending Spectral Response into the Deep Short-Wave Infrared.

III-V colloidal quantum dots (CQDs) with large and well-controlled diameters are of interest in applications from red light emitters to deep short-wave infrared (SWIR) photodetectors, yet nanocluster-seeded syntheses often encounter an empirical "size wall" in the ∼5-8 nm diameter range. Here, we identify monomer release and transfer from nanoclusters to growing seeds as a key kinetic constraint during extended injection and growth. We show that short-chain carboxylic acids (SCCAs) can act as transient ligands that increase nanocluster lability and enhance monomer transfer, enabling continuous growth beyond this plateau. H NMR using C-labeled acetic acid quantifies a ∼1:1 myristate/acetate ligand ratio on the initial nanoclusters, with diffusion-ordered spectroscopy (DOSY) supporting the transient surface association of acetate; H NMR of CQDs grown with deuterated acetic acid (CDCOOH) shows no residual deuterium signal, indicating that acetate promotes growth without persisting on the final CQD surface. Across a C1 (formic) to C4 (butyric) SCCA screen, C2 (acetic) acid provides the best balance of volatility and lability. Incorporating SCCAs at the nanocluster stage yields InAs CQDs with excitonic features extending up to 1800 nm. XPS and indium K-edge XANES/EXAFS analyses indicate diminished oxide-related features in acetic acid-derived samples compared with size-matched controls. We fabricate photodetectors with a 1520 nm exciton, extending InAs CQD photodetection into the deep SWIR.