Ligand Effects on the Structure and Optoelectronic Properties of InP Magic-Sized Clusters

Semiconductor Magic-Sized Clusters (MSCs) are an expanding class of colloidal nanoparticles with increasingly compelling properties for applications in conventional and quantum optoelectronics.¹ MSCs earn their lofty name from discrete growth in solution and offer access to colloidal ensembles of identical particles, free of the size or shape heterogeneity typical of conventional quantum dots.² The small size of MSCs, typically <3nm, results in optoelectronic properties with high sensitivity to small perturbations in cluster structure, surface chemistry, or surrounding environment which offers vast potential for design control of their emissive properties. MSCs are also a model system for detailed characterization efforts, as the nanoparticle itself is often <100 atoms, and atomic precision enables confident small box modeling of scattering data taken on powders or dispersed nanoparticle solutions. Here we present the effects of various carboxylate terminating ligands on the structure, rigidity, and optoelectronic properties of the low symmetry In₃₇P₂₀ MSC.^3,4 We combine Pair Distribution Function analysis from X-ray total scattering with Extended X-ray Absorption Fine Structure results to reveal steric crowding in ligand shell alters the average structure and bonding rigidity of the MSC. We further employ quasielastic neutron scattering to reveal the spatial extent, timescales, and activation energies of relaxational ligand motions on the MSC surface. Altogether these characterization efforts seek to correlate ligand effects to ligand-driven changes observed in both steady state and time resolved spectroscopy, and are intended to be key transferable insights in the pursuit of narrow, high efficiency PL emission from this exciting class of solution-processed semiconductors.
[1] Ripberger, H. H. et al. Acc. Mater. Res. accountsmr.4c00064 (2024) [2] Pun, A. B. et al. Acc. Chem. Res. 54, 1545–1554 (2021)
[3] Gary, D. C. et al. J. Am. Chem. Soc. 138, 1510–1513 (2016) [4] Sandeno, S. F. et al. J. Am. Chem. Soc. jacs.3c10203 (2024)