title: Soft ligand stabilized gold nanoparticles: incorporation of bipyridyls and two-dimensional assembly.
abstract: OBJECTIVE
  The synthesis of gold nanoparticles (AuNPs) in organic solvents without addition of surfactant may be achieved without the use of strong capping agents in the presence of soft ligands from the starting materials. Through post synthesis surface modification with ligands having moderate or strong affinity, the soft ligands should be displaced, allowing for manipulation of the AuNP size, size distribution, as well as the interparticle spacing.
  
  
  METHODS
  Synthesis of gold nanoparticles was undertaken using the reducing agent 9-borabicyclo[3.3.1]nonane without addition of stabilizing ligands. Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the NPs. The interparticle spacing in 2D assemblies of the NPs was correlated with localized surface plasmon resonance (LSPR) shifts exhibited by the NPs in solution.
  
  
  RESULTS
  Soft-ligand-stabilized AuNPs in a size range of 3-5 nm were generated at a slow rate. The soft ligands were found to be chloride (Cl(-)) ions and triethylphosphine (Et3P). Bipyridyl and thiol ligands displaced the weakly adsorbed soft ligands. Thiolate-stabilized AuNPs formed long range 2-D assemblies with regular interparticle spacing (edge-to-edge). UV-vis spectroscopy analysis shows the thiolated AuNPs exhibited an exponential localized wavelength (λmax) decay dependence on the alkylthiolate chain length, indicating an increase in the interparticle spacing.
authors.affiliation: Department of Chemistry, University of Utah, 315 South 1400 East, RM 2020, Salt Lake City, UT 84112, USA.
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Shem
authors.affiliation: Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, IN 46202-3274, USA.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Sardar
authors.affiliation: Department of Chemistry, University of Utah, 315 South 1400 East, RM 2020, Salt Lake City, UT 84112, USA. Electronic address: shumaker-parry@chem.utah.edu.
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Shumaker-Parry
mesh_terms: D015082:2,2'-Dipyridyl / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D008024:Ligands; D053768:Metal Nanoparticles; D046529:Microscopy, Electron, Transmission; D056951:Photoelectron Spectroscopy; D013056:Spectrophotometry, Ultraviolet; D019265:Spectroscopy, Near-Infrared
chemical_list: D008024:Ligands; D015082:2,2'-Dipyridyl; D006046:Gold
keywords: 9-BBN; Bipyridyl-functionalized AuNPs; Interparticle spacing; Soft ligand; Thiol-functionalized AuNPs; Two-dimensional assembly