Study of metal nanoparticles stabilised by mixed ligand shell: a striking blue shift of the surface-plasmon band evidencing the formation of Janus nanoparticles

Abstract

Mixed ligand shells stabilising gold nanoparticles have been synthesised using diphenylphosphinine 1 (phosphinine is the phosphorus equivalent of pyridine) and a family of thiol ligands: mercaptoundecanoic acid (2), dodecanethiol (3) and thiophenol (4). Phosphinine 1 and thiols 2 and 3 feature little affinity to one another, so we expected them to self-segregate in pure domains. We studied the resulting particles with UV-vis, FT-IR and TEM (transmission electron microscopy). The plasmonic band of those particles features an unprecedented blue shift compared to the pure ligand-shell nanoparticles, strongly suggesting a polarisation of the particle caused by ligand segregation. FT-IR evidences the formation of nano domains of ligands in pure phase, and some self-aggregation behaviour of the nanoparticles themselves was observed by TEM.