Hybrid Metal-Ligand Interfacial Dipole Engineering of Functional Plasmonic Nanostructures for Extraordinary Responses of Optoelectronic Properties

Programmable manipulation of inorganic-organicinterfacialelectronic properties of ligand-functionalized plasmonic nanoparticles(NPs) is the key parameter dictating their applications such as catalysis,photovoltaics, and biosensing. Here we report the localized surfaceplasmon resonance (LSPR) properties of gold triangular nanoprisms(Au TNPs) in solid state that are functionalized with dipolar, conjugatedligands. A library of thiocinnamate ligands with varying surface dipolemoments were used to functionalize TNPs, which results in & SIM;150nm reversible tunability of LSPR peak wavelength with significantpeak broadening (& SIM;230 meV). The highly adjustable chemicalsystem of thiocinnamate ligands is capable of shifting the Au workfunction down to 2.4 eV versus vacuum, i.e., & SIM;2.9 eV lowerthan a clean Au (111) surface, and this work function can be modulatedup to 3.3 eV, the largest value reported to date through the formationof organothiolate SAMs on Au. Interestingly, the magnitude of plasmonicresponses and work function modulation is NP shape dependent. By combiningfirst-principles calculations and experiments, we have establishedthe mechanism of direct wave function delocalization of electronsresiding near the Fermi level into hybrid electronic states that aremostly dictated by the inorganic-organic interfacial dipolemoments. We determine that both interfacial dipole and hybrid electronicstates, and vinyl conjugation together are the key to achieving suchextraordinary changes in the optoelectronic properties of ligand-functionalized,plasmonic NPs. The present study provides a quantitative relationshipdescribing how specifically constructed organic ligands can be usedto control the interfacial properties of NPs and thus the plasmonicand electronic responses of these functional plasmonics for a widerange of plasmon-driven applications.