Enhanced Fluorescence of Epicocconone in Surfactant Assemblies as a Consequence of Depth-Dependent Microviscosity

The extents of fluorescence enhancement of epicocconone are found to be different in the micelles of the surfactants sodium dodecyl sulfate (SDS) and Triton X100 (TX 100). A decrease in fluorescence, observed in the cationic cetyltrimethylammonium bromide (CTAB) micelles, is rationalized by the formation of anions of the fluorophore at the Stern layer. To understand the difference in the effects of SDS and TX 100, the nature of the excited-state process in the fluorophore has been investigated by fluorescence spectroscopy, supported by complementary quantum chemical calculations. The excited-state dynamics of epicocconone is found to depend on polarity and viscosity of the medium, with a more pronounced dependence on viscosity. An inspection of the molecular orbitals involved in the electronic absorption of the molecule reveals the possibility of photoisomerization, which conforms to the observed solvent dependence of the fluorescence spectral properties. An apparent mismatch between trends observed in steady-state spectra and those in temporal decays indicates a significant contribution of an ultrafast component, which cannot be detected in the time resolution of our instrument. The viscosity dependence of the fluorescence quantum yields provides an explanation for the difference in the extents of fluorescence enhancement in the two micelles, in the light of location of the fluorophore at different depths of the micelle. The enhancement of fluorescence, with an unchanged fluorescence maximum, opens up the possibility that the fluorophore could be a useful dual emitting marker for fluorescence microscopy of heterogeneous systems, as the fluorescence of protein-bound epicocconone has been previously reported to be significantly red-shifted

Pd-Coated Au Triangular Nanoprisms as Catalysts for Hot-Carrier-Driven Photochemistry

Bimetallic nanoparticle dyads consisting of a plasmonic core and a catalytic metal shell have attracted significant attention in the context of solar-driven photocatalysts. However, a pertinent design considering both the optical properties of the core and shell and the thickness of the shell material is scarce. Through experiments and simulations, we demonstrated that the photocatalytic efficiency of the Au triangular nanoprisms@Pd (AuTP@Pd) core@shell dyad largely depends on the thickness of the catalytic metal shell. For a lower thickness, the dyad showed enhanced photocatalytic activity compared to bare AuTPs. However, for a higher thickness, the dyad’s catalytic activity reduced drastically and showed even lower catalytic activity than pristine AuTPs. From simulations, we showed that for a thin Pd layer, charge carriers were essentially generated at the Pd shell itself and thereby could be easily extracted and utilized. However, a thicker Pd shell screened the plasmonic core and reduced the charge-carrier formation. These findings will be relevant for the optimization of the bimetallic plasmonic catalyst design

Photoelectrochemical Water Oxidation with Plasmonic Au@MnOx Core–Shell Nanoparticles

Development of robust and efficient photocatalytic constructs to facilitate the water oxidation reaction (WOR) remains essential for various renewable energy technologies. Here we report on developing Au@MnOx core–shell nanoparticles that perform the electrochemical WOR at a low onset overpotential requirement of approximately 230 mV. Under visible light excitation, the WOR activity of the Au@MnOx catalytic construct showed further improvement with the decrease of the overpotential requirement and generation of a photocurrent of 128 μA/cm2 at 1 V applied potential. The incident photon to photocurrent conversion efficiency (IPCE) was found to be 0.1%. The Au@MnOx core–shell nanoparticles were also found to be stable under prolonged photoexcitation up to 2000 s

Establishing Surface Charge as a Key Control Parameter for Linker-Driven Tip-Specific Ordering of Anisotropic Gold Nanoparticles

Here, we show that nanoparticles’ surface charge is a key factor that determines their tip-specificity in a covalently linked assembly of anisotropic plasmonic nanoparticles. We developed a strategy to controllably tune the surface charge of gold nanoparticles over a broad ζ potential range between −5 and −35 mV using simple acid–base chemistry and showed that dithiol-driven, end-to-end linked dimers of gold nanorods were formed reproducibly within a ζ potential range between −10 and −17 mV in acetonitrile medium. Below this ζ potential range, nanoparticles collapse together to form large clusters without any tip-specificity. For ζ potentials above this range, electrostatic repulsion prevents them from binding to each other. Our approach of using the surface charge of nanoparticles as a key control parameter for achieving tip-specificity is quite versatile and works for different anisotropic nanoparticles including gold nanorods of different aspect ratios and gold nanobipyramids

Porous Plasmonic Au–Ag@Au Nanostructures for Photoelectrochemical Methanol Oxidation

Pt and its alloys are commonly used as catalysts for electrochemical methanol oxidation reaction (MOR), owing to their high efficiencies. However, the high cost and instability of these catalysts due to poisoning from intermediates restrict their large-scale applications. Here we study plasmonic porous Au–Ag nanoparticles toward electrochemical and photoelectrochemical MOR. We synthesized Au–Ag@Au nanostructures that consist of the Au nanorod core and Au–Ag shell, where nanopores were created via selectively etching Ag atoms. The porous Au–Ag@Au nanostructures demonstrated significantly better MOR activity compared to their nonporous counterpart. Importantly, the presence of pores drastically suppressed the poisoning from the intermediate species, leading to a large improvement of their electrochemical stability. Furthermore, the porous Au–Ag@Au constructs showed strong enhancement of their catalytic activity under visible as well as near-infrared (NIR) excitations with generation of photocurrents of 1.23 and 0.45 mA mg–1 cm2, and with incident photon to current conversion efficiencies of 1.43 and 0.34% for visible and NIR wavelengths, respectively. Generation of photocurrents was shown to be predominantly due to the plasmonic hot-hole-assisted MOR

Active Modulation of Nanorod Plasmons

Confining visible light to nanoscale dimensions has become possible with surface plasmons. Many plasmonic elements have already been realized. Nanorods, for example, function as efficient optical antennas. However, active control of the plasmonic response remains a roadblock for building optical analogues of electronic circuits. We present a new approach to modulate the polarized scattering intensities of individual gold nanorods by 100% using liquid crystals with applied voltages as low as 4 V. This novel effect is based on the transition from a homogeneous to a twisted nematic phase of the liquid crystal covering the nanorods. With our method it will be possible to actively control optical antennas as well as other plasmonic elements

Correction to Luminescence Quantum Yield of Single Gold Nanorods

Correction to Luminescence Quantum Yield of Single Gold Nanorod

Use of Single-Molecule Plasmon-Enhanced Fluorescence to Investigate Ligand Binding to G‑Quadruplex DNA

Single-molecule measurements are crucial for studying the interactions between G-quadruplex (GQ) DNA and ligands, as they provide higher resolution and sensitivity compared to those of bulk measurements. In this study, we employed plasmon-enhanced fluorescence to investigate the real-time interaction between the cationic porphyrin ligand TmPyP4 and different topologies of telomeric GQ DNA at the single-molecule level. By analyzing the time traces of the fluorescence bursts, we extracted dwell times for the ligand. For parallel telomeric GQ DNA, the dwell time distribution followed a biexponential fit, yielding mean dwell times of 5.6 and 18.6 ms. For the antiparallel topology of human telomeric GQ DNA, plasmon-enhanced fluorescence of TmPyP4 was observed, with dwell time distributions following a single-exponential fit and a mean dwell time of 5.9 ms. Our approach allows the nuances of GQ–ligand interactions to be captured and holds promise for studying weakly emitting GQ ligands at the single-molecule level

Influence of the Substrate on the Mobility of Individual Nanocars

We monitored the mobility of individual fluorescent nanocars on three surfaces: plasma cleaned, reactive ion etched, and amine-functionalized glass. Using single-molecule fluorescence imaging, the percentage of moving nanocars and their diffusion constants were determined for each substrate. We found that the nanocar mobility decreased with increasing surface roughness and increasing surface interaction strength

Efficient Harvesting of >1000 nm Photons to Hydrogen via Plasmon-Driven Si–H Activation in Water

Efficient harvesting of the near-infrared (NIR) portion of the sunlight remains key to the development of a solar-to-fuel renewable energy infrastructure. Here we report on the development of first pristine plasmonic nanoparticle-assisted NIR-II photon-to-hydrogen production strategy that does not require any external electric bias or sacrificial chemicals. Our strategy utilizes a robust and easily scalable plasmonic substrate containing pristine gold nanoprisms to drive photocatalytic Si–H activation in water, producing hydrogen and silanol. The photocatalytic substrate exhibited excellent photon-to-hydrogen conversion efficiency of ∼0.85–1.45% for wavelengths between 1000 and 1700 nm while producing hydrogen at 132 μL min–1 mg–1 Au. The robustness and easy scalability of our catalyst fabrication, ease of usage, excellent photon-to-hydrogen production efficiency, and no requirement of additional energy bias make our strategy highly relevant for applications in the alternative energy sector