Noble metal nanoparticles have been of tremendous interest due to their intriguing size- and shape-dependent plasmonic and catalytic properties. Combining tunable plasmon resonances with superior catalytic activities on the same metallic nanoparticle, however, has long been challenging because nanoplasmonics and nanocatalysis typically require nanoparticles in two drastically different size regimes. Here, we demonstrate that creation of high-index facets on subwavelength metallic nanoparticles provides a unique approach to the integration of desired plasmonic and catalytic properties on the same nanoparticle. Through site-selective surface etching of metallic nanocuboids whose surfaces are dominated by low-index facets, we have controllably fabricated nanorice and nanodumbbell particles, which exhibit drastically enhanced catalytic activities arising from the catalytically active high-index facets abundant on the particle surfaces. The nanorice and nanodumbbell particles also possess appealing tunable plasmonic properties that allow us to gain quantitative insights into nanoparticle-catalyzed reactions with unprecedented sensitivity and detail through time-resolved plasmon-enhanced spectroscopic measurements.

Metal-semiconductor hybrid heteronanostructures may exhibit synergistically reinforced optical responses and significantly enhanced optical tunability that essentially arise from the unique nanoscale interactions between the metal and semiconductor components. Elaboration of multi-component hybrid nanoparticles allows us to achieve optimized or diversified material functionalities through precise control over the dimension and morphology of the constituent building units, on one hand, and through engineering their relative geometrical arrangement and interfacial structures, on the other hand. Here we study the geometry-dependent optical characteristics of metal-cuprous oxide (Cu(2)O) core-shell hybrid nanoparticles in great detail through combined experimental and theoretical efforts. We demonstrate that several important geometrical parameters, such as shell thickness, shell crystallinity, shell porosity, and core composition, of the hybrid nanoparticles can be tailored in a highly precise and controllable manner through robust wet chemistry approaches. The tight control over the particle geometries provides unique opportunities for us to develop quantitative understanding of how the dimensions, morphologies, and electronic properties of the semiconducting shells and the geometry and compositions of the metallic cores affect the plasmon resonance frequencies, the light scattering and absorption cross sections, and the overall extinction spectral line shapes of the hybrid nanoparticles. Mie scattering theory calculations provide further insights into the origin of the geometrically tunable optical responses and the interesting extinction spectral line shapes of the hybrid nanoparticles that we have experimentally observed.

While great success has been achieved in fine-tuning the aspect ratios and thereby the plasmon resonances of cylindrical Au nanorods, facet control with atomic level precision on the highly curved nanorod surfaces has long been a significantly more challenging task. The intrinsic structural complexity and lack of precise facet control of the nanorod surfaces remain the major obstacles for the atomic-level elucidation of the structure-property relationships that underpin the intriguing catalytic performance of Au nanorods. Here we demonstrate that the facets of single-crystalline Au nanorods can be precisely tailored using cuprous ions and cetyltrimethylammonium bromide as a unique pair of surface capping competitors to guide the particle geometry evolution during nanorod overgrowth. By deliberately maneuvering the competition between cuprous ions and cetyltrimethylammonium bromide, we have been able to create, in a highly controllable and selective manner, an entire family of nanorod-derived anisotropic multifaceted geometries whose surfaces are enclosed by specific types of well-defined high-index and low-index facets. This facet-controlled nanorod overgrowth approach also allows us to fine-tune the particle aspect ratios while well-preserving all the characteristic facets and geometric features of the faceted Au nanorods. Taking full advantage of the combined structural and plasmonic tunability, we have further studied the facet-dependent heterogeneous catalysis on well-faceted Au nanorods using surface-enhanced Raman spectroscopy as an ultrasensitive spectroscopic tool with unique time-resolving and molecular finger-printing capabilities.

A series of cationic iridium(III) complex salts, 1−5, were synthesized containing different phenanthroline derivatives. Their photophysical and electrochemical properties were investigated. The influences of anions and proton on the photophysical and electrochemical properties were also studied in detail. Upon addition of CF3COOH, the emission wavelength was significantly red-shifted and the emission color changed from yellow to red. In addition, the addition of F-, CH3COO-, and H2PO4 - can also cause significant variations in UV−vis absorption and emission spectra. Upon addition of F-, CH3COO-, and H2PO4 -, the solution colors of 1−3 changed from yellow-green to brown and the emission of 1−3 was quenched completely, which can be observed by the naked eye.