Self -assembly and optical properties of resorcinarene encapsulated gold nanoparticles

Resorcinarenes are excellent surfactants for enhancing the dispersion and self-assembly gold nanoparticles. Tetrathiol cavitands such as 8 and 13 enhance the dispersion and robustness of midnanometer-sized gold particles suspended in organic solvents. Tetra-C-thiomethyl cavitand 13 is a superior dispersant over tetra-C-thiol cavitand 8 under the conditions examined. However, cavitand 8 provides excellent dispersion control of gold nanoparticles at the air-water interface and enables their spontaneous organization into two-dimensional arrays. In addition, we have studied the self-assembly of resorcinarene-encapsulated gold nanoparticles as a function of surface charge and surfactant structure. The degree of monolayer formation and 2D order within the self-assembled nanoparticle arrays is strongly influenced by the amount and type of electrolyte (chloride and/or citrate) adsorbed on the nanoparticle surface. Resorcinarenes with strongly chemisorptive headgroups promote the self-assembly of 2D arrays. The gold nanoparticle arrays exhibit size-dependent extinction maxima which shift toward near-infrared wavelengths with increasing periodicity. Surface-enhanced Raman scattering (SERS) also varies greatly as a function of periodicity and incident wavelength, with empirical enhancement factors (G) ranging from 104 to over 107. The majority of the enhanced Raman scattering is most likely produced by localized field effects in the crevices and cavities of the arrays, whose depths and aspect ratios can be tuned by changing the unit particle size. The resorcinarene-coated gold nanoparticle arrays can detect volatile organic compounds and molecules in aqueous environments. Moreover, the resorcinarene-coated nanostructured films were stable in air and water at ambient temperatures and show no appreciable loss in SERS activity over a period of several months.