UC Irvine

In the recent push toward single molecule spectroscopy and photochemistry, plasmonic nanostructures have emerged as an attractive and experimentally tractable design. We have developed a versatile experimental platform based on plasmonic core-shell nanocrystal dimers (termed nantenna) using colloidal assembly and atomic layer deposition (ALD) to achieve functional, stable structures for single-molecule time-resolved studies of charge transfer reactions and chemical transformations important in (photo)electrocatalysis and plasmon-driven chemistry.

The steady-state SERS study has been performed on two platforms as a proof-of-concept: Platform I consists of Ag/TiO2/N719/TiO2; Platform II consists of Au/TiO2/DBDT/Al2O3. Later, we explored the reversible assembly of citrate-capped Au NCs and hexa(ethylene glycol) dithiol (HEGDT). The dithiol-triggered polymerization of the Au NCs results in complete precipitation of the NCs in a short time. However, we have shown that by injecting an appropriate oxidizing reagent into the solution, we can oxidize the dithiols to disulfonic acids, resulting in the destruction of the dithiol linkers and complete depolymerization of the Au NCs to re-form a stable colloidal solution of individual Au NCs. We have studied the polymerization and depolymerization process with a suite of methods (optical absorption spectroscopy, FT-IR, DLS, SAXS, XPS, TEM, NMR, mass spectrometry, zeta potential, and pH measurements) to establish details of the chemistry and learn how to arrest the polymerization reaction, with a goal of a stable colloidal suspension of dimers.

Lastly, we investigated a facile synthesis of 100% dimers by triggering the surface thiol-ene click reaction under plasmonic heating around dimers. The PEGylated maleimides and acrylates are identified as the most effective reagent to passivate the dithiol-triggered aggregation through NMR kinetics study and click reaction in Au NCs suspension. The initial study of illuminating Au NCs monomers at different wavelengths demonstrates the plasmonic heating effect successfully.