Recent advances in understanding the theoretical and experimental properties of excitons and plasmons have led to several technological breakthroughs. Though emerging from different schools of research, the parallels they possess both in their isolated and assembled forms are indeed interesting. Employing the larger framework of the dipolar coupling model, these aspects are discussed based on the excitonic transitions in chromophores and plasmonic resonances in noble metal nanostructures. The emergence of novel optical properties in linear, parallel, and helical assemblies of chromophores and nanostructures with varying separation distances, orientations, and interaction strengths of interacting dipolar components is discussed. The very high dipolar strengths of plasmonic transitions compared to the excitonic transitions, arising due to the collective nature of the electronic excitations in nanostructures, leads to the emergence of hot spots in plasmonically coupled assemblies. Correlations on the distance dependence of electric field with Raman signal enhancements have paved the way to the development of capillary tube-based plasmonic platforms for the detection of analytes.

Plasmonic metal nanostructures have garnered rapidly increasing interest as heterogeneous photocatalysts, facilitating chemical bond activation and overcoming the high energy demands of conventional thermal catalysis. Here we report the highly efficient plasmonic photocatalysis of the direct decomposition of hydrogen sulfide into hydrogen and sulfur, an alternative to the industrial Claus process. Under visible light illumination and with no external heat source, up to a 20-fold reactivity enhancement compared to thermocatalysis can be observed. The substantially enhanced reactivity can be attributed to plasmon-mediated hot carriers (HCs) that modify the reaction energetics. With a shift in the rate-determining step of the reaction, a new reaction pathway is made possible with a lower apparent reaction barrier. Light-driven one-step decomposition of hydrogen sulfide represents an exciting opportunity for simultaneous high-efficiency hydrogen production and low-temperature sulfur recovery, important in many industrial processes.

Light–matter interactions in chromophore-bound nanoparticles result in various plasmon-mediated processes such as energy transfer, electron transfer, and enhanced emission. Although significant, plexcitonic states formed as a result of noncovalent interactions between plasmonic nanoparticles and chromophores are seldom sighted. Since the binding of chromophores via noncovalent interactions is predominantly an equilibrium process, the finer features of the newly formed plexcitonic states are often masked by the excessive absorption of the unbound chromophoric systems. Herein, we adopt differential extinction spectroscopy to bring out the otherwise hidden plexcitonic states in chromophore-bound plasmonic systems: cyanine and squaraine dyes bound on plasmonic nanoparticles through various noncovalent interactions. These chromophore-bound plasmonic nanoparticles in water showed a single peak that is broadened when water is used as the reference; however, they displayed a conspicuous Rabi splitting with the chromophoric dye solution as the reference. The formation of plexcitonic states is evident from the well-defined splitting of the extinction band in the differential extinction spectrum of cyanine dyes bound on Ag nanoparticles/Au nanorods. The nature of the plexcitonic states is further established by finite-difference time-domain simulations and a two-state model. The results presented herein ascertain that the plasmon–exciton coupling in chromophore-functionalized metal nanoparticles should be well considered while investigating various plasmon-assisted photophysical processes.

Aluminum nanocrystals (Al NCs) with a welldefined size and shape combine unique plasmonic properties with high earth abundance, potentially ideal for applications where sustainability and cost are important factors. It has recently been shown that single-crystal Al {100} nanocubes can be synthesized by the decomposition of AlH 3 with Tebbe's reagent, a titanium-(IV) catalyst with two cyclopentadienyl ligands. By systematically modifying the catalyst molecular structure, control of the NC growth morphology is observed spectroscopically, as the catalyst stabilizes the {100} NC facets. By varying the catalyst concentration, Al NC faceted growth is tunable from {100} faceted nanocubes to {111} faceted octahedra. This study provides direct insight into the role of catalyst molecular structure in controlling Al NC morphology.

The synthesis of Al nanocrystals (Al NCs) is a rapidly expanding field, but there are few strategies for size and morphology control. Here we introduce a dual catalyst approach for the synthesis of Al NCs to control both NC size and shape. By using one catalyst that nucleates growth more rapidly than a second catalyst whose ligands affect NC morphology during growth, one can obtain both size and shape control of the resulting Al NCs. The combination of the two catalysts (1) titanium isopropoxide (TIP), for rapid nucleation, and (2) Tebbe’s reagent, for specific facet-promoting growth, yields {100}-faceted Al NCs with tunable diameters between 35 and 65 nm. This dual-catalyst strategy could dramatically expand the possible outcomes for Al NC growth, opening the door to new controlled morphologies and a deeper understanding of earth-abundant plasmonic nanocrystal synthesis.