Passivation by Ultimate Ligand-Surface Activation Rationalized by NMR

Dynamic nuclear polarization (DNP)-enhanced solid-state NMR spectroscopy has proven in recent years to be a powerful technique for the characterization of challenging solid materials and their interfaces. Substantially increased sensitivity of NMR experiments becomes possible through DNP, where the large polarization of unpaired electron spins is transferred to the desired nuclei. For inorganic nanoparticles (NPs) surrounded with sources of unpaired electrons, known as polarizing agents, polarization transfers are mainly to their surfaces. Therefore, surface selectivity, in addition to increased sensitivity, is achieved and this can be used to study the surface chemistry of NPs. The capping of NPs with inorganic ligands (ILs), rather than conventional organic ligands, has been proposed to improve charge carrier lifetime in solids composed of assemblies of NPs, usually termed colloidal quantum dot solids (CQDSs). Substantial increases in transport properties and method versatility have led researchers to explore many types of IL to improve the mobility of charge carriers. However, gaining a detailed understanding of the surface chemistry of IL-capped NPs remains a challenging task and is thus still lacking. This project aims to correlate the surface chemistry and interfaces of ligand-capped CQDSs with their performance. Surface characterization of IL-capped NPs will be carried out by advanced DNP-enhanced solid-state NMR spectroscopy. Photoluminescence and conductivity measurements will indicate the effect on charge carrier lifetimes in assembled CQDSs. Therefore, the proposed research will result in a breakthrough atomic-level understanding of how IL choice and surface chemistry influences charge transport and will lead to a generalized method for achieving single-crystal-grade mobility values in CQDSs.