The Dynamic Organic/Inorganic Interface of Colloidal PbS Quantum Dots

Abstract

Colloidal quantum dots are composed of nanometer‐sized crystallites of inorganic semiconductor materials bearing organic molecules at their surface. The organic/inorganic interface markedly affects forms and functions of the quantum dots, therefore its description and control are important for effective application. Herein we demonstrate that archetypal colloidal PbS quantum dots adapt their interface to the surroundings, thus existing in solution phase as equilibrium mixtures with their (metal‐)organic ligand and inorganic core components. The interfacial equilibria are dictated by solvent polarity and concentration, show striking size dependence (leading to more stable ligand/core adducts for larger quantum dots), and selectively involve nanocrystal facets. This notion of ligand/core dynamic equilibrium may open novel synthetic paths and refined nanocrystal surface‐chemistry strategies.

Ligand-Induced Shape Transformation of PbSe Nanocrystals

“…These findings contrast with those reported in the literature, where for PbS NCs, the presence of oleic acid and hydroxide on different facets of the surface of NCs has been reported. 17 , 25 We remark here that the hydroxide peak found by Grisorio et al 25 cannot be attributed to oxidation of the dots (see Figure S5 ). As Grisorio et al claimed, it can be the result from the use of Pb(oleate) 2 -hydrate in their advanced synthesis procedure for PbS nanocrystals.…”

From ligands to binding motifs and beyond; the enhanced versatility of nanocrystal surfaces

“…27 Importantly, Owen et al realized that the whole MX2 unit can also be regarded a Z-type ligand since cadmium carboxylate is a Lewis acid. 12 The Z/MX2 equivalence was confirmed for CdS, 30 CdTe, 31 PbSe and PbS 28,32 NCs and profoundly changes the way the chemical stability of the ligand shell must be understood. Whereas X-type ligands are unable to desorb from a metal rich NC, the Z-ligands are potentially more labile.…”

“…Whereas X-type ligands are unable to desorb from a metal rich NC, the Z-ligands are potentially more labile. In the case of PbS NCs, lead oleate was shown to spontaneously desorb upon change of solvent polarity 32 or dilution: 30 NC(MX 2 ) ⇌ NC + MX 2 In contrast, the cadmium carboxylate capping is tightly bound to CdSe NCs. However, it was possible to displace this Z/MX2-ligand by the addition of amines.…”

Colloidal Bismuth Chalcohalide Nanocrystals

“…The replacing ligands improved the colloidal stability of both the BiSBr NC dispersions, although an excess of such ligands, as suggested by the narrow linewidth and the multiplicity of the NMR resonances, [41] was necessary to achieve long-term stability (Figure S44). In particular, NCs coordinated by Me 2 Do 2 N + Br À ligands could be readily redispersed in apolar solvents, such as toluene, by gentle shaking with no appreciable amount of material sticking to the glass vial walls.…”