Small gold nanoparticles (AuNPs, ∼1.4–2.2 nm core diameters) exist at an exciting interface between molecular and metallic electronic structures. These particles have the potential to elucidate fundamental physical principles driving nanoscale phenomena and to be useful in critical applications ranging from catalysis to bioimaging. Here, we first demonstrate the surface chemistry-dependent photoluminescent properties of aqueous, phosphine-terminated AuNPs (core diameter = 1.7 ± 0.4 nm) after ligand exchange with a variety of sulfur-containing molecules. No emission is observed from these particles prior to ligand exchange, however the introduction of sulfur-containing ligands initiates photoluminescence, with quantum yields approaching 4% for the smallest ligands studied. With correlation between surface chemistry and AuNP emission properties in hand, the rational design of AuNPs for energy transfer applications is demonstrated by using NIR-emitting AuNPs to sensitize ytterbium (Yb) emission. The AuNP-Yb conjugate combines the high molar absorptivity (1.21x103 M-1cm-1) and broad excitation features of AuNPs with the narrow emission properties of the Yb: the AuNP-Yb conjugate exhibits a full width at half maximum of 62 nm with a brightness (quantum yield x molar absorptivity) of 1.9x103 M-1cm-1. Mercaptoalkanoic acid ligands of different chain lengths are used to systematically control the distance between the AuNP and Yb, yielding distance-dependent results that are consistent with a Dexter energy transfer mechanism. Further, the reversibility of this energy transfer process is also reported. Taken together, these experiments demonstrate surface chemistry as a powerful tool for the design of functional nanomaterials.

Using gold nanoparticle surface chemistry to control electronic behavior: Towards energy transfer applications

254th National Meeting (2017)

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