Surface Plasmon Enhancement At A Liquid-Metal-Liquid Interface

Herein, we report the first experimental demonstration of surface plasmon enhancement at a liquid-metal-liquid interface using a pseudo-Kretschmann geometry. Pumping gold nanoparticle clusters at the interface of a p-xylene-water mixture, we were able to measure a fluorescence enhancement of three orders of magnitude in Rose Bengal at an excitation wavelength of 532 nm. The observed increase is due to the local electric field enhancement and the reduction of the fluorescence lifetime of dye molecules in the close vicinity of the metal surface. Theoretical modeling using the T-matrix method of the electric field intensity enhancement of emulated surfaces supports the experimental results. This new approach will open a new road for the study of dynamic systems using plasmonics. © Springer Science+Business Media, LLC 2007

Fluorescence Emission Of Disperse Red 1 In Solution At Room Temperature

In this article, we report the fluorescence emission of Disperse Red 1 in solution at room temperature and pumping at 532 nm with a 25 mW diode laser. We have measured its fluorescence quantum yield in methanol, ethylene glycol, glycerol, and phenol obtaining values as high as 10-3 in the aliphatic alcohols. The excitation spectra of Disperse Red 1 in all four solvents as well as its excitation anisotropy in glycerol are presented. Applying a Gaussian decomposition method to the absorption spectra along with the support from the excitation spectra, the positions of the different transitions in this pseudo-stilbene azobenzene dye were determined. Solvatochromic and isomerization constraint effects are discussed. Calculations using density functional theory at TD-B3LYP/6-31G*//HF/6-31G* level were performed to interpret the experimental observations. © 2008 American Chemical Society

Sequestering High-Energy Electrons to Facilitate Photocatalytic Hydrogen Generation in CdSe/CdS Nanocrystals

The photocatalytic H₂O splitting activities of CdSe and CdSe/CdS core/shell quantum dots are contrasted. CdSe/CdS core/shell quantum dots constructed from 4.0 nm CdSe quantum dots are shown to be strongly active for visible-light-driven photocatalytic H₂ evolution in 0.1 M Na₂S/Na₂SO₃ solution with a turnover number of 9.94 after 5 h at 103.9 μmol/h. CdSe quantum dots themselves are only marginally active in 0.1 M Na₂S/Na₂SO₃ solution with a turnover number of 1.10 after 5 h at 11.53 μmol/h, while CdSe quantum dots in pure H₂O are found to be completely inactive. Broad-band transient absorption spectroscopy is used to elucidate the mechanisms that facilitate the enhancement in the CdSe core/shell quantum dots, which is attributed to passivation of surface-deep trap states with energies lying below the reduction potential necessary for H₂O reduction. Thus, surface trapping dynamics and energetics can be manipulated to dictate the photocatalytic activities of novel CdSe quantum dot based photocatalytic materials

Red States versus Blue States in Colloidal Silicon Nanocrystals: Exciton Sequestration into Low-Density Traps

The ultrafast exciton photodynamics of red-emitting and blue-emitting colloidal Si nanocrystals are contrasted under low (1.5 mJ/cm²) and high (9.1 mJ/cm²) excitation powers with broadband transient absorption spectroscopy. While the low-power initiated transient signals differ strongly for the two samples, the high-power signals exhibit similar nonmonotonic kinetics, resulting in a new population formed on a 10 to 30-ps time scale with a sample independent spectrum and decay kinetics. This phenomenon is ascribed to the saturation of low-density red-emitting and blue-emitting traps via a state-filling mechanism to populate new meta-stable states at higher excitation powers. The states responsible for blue emission and high-power populations are ascribed to traps from low-density nitrogen and oxygen impurities, respectively, and share similar charge-transfer character with the silicon nanocrystal core

Chemical Inhomogeneity in the Ultrafast Dynamics of the DXCF Cyanobacteriochrome Tlr0924

Cyanobacteriochromes (CBCRs) are diverse biliprotein photosensors distantly related to the red/far-red photoreceptors of the phytochrome family. There are several subfamilies of CBCRs, displaying varied spectral responses spanning the entire visible region. Tlr0924 belongs to the DXCF subfamily that utilizes the Cys residue in a conserved Asp-Xaa-Cys-Phe (DXCF) motif to form a second covalent linkage to the chromophore, resulting in a blue-absorbing dark state. Photoconversion leads to elimination of this linkage, resulting in a green-absorbing photoproduct. Tlr0924 initially incorporates phycocyanobilin (PCB) as a chromophore, exhibiting a blue/orange photocycle, but slowly isomerizes PCB to phycoviolobilin (PVB) to yield a blue/green photocycle. Ultrafast transient absorption spectroscopy was used to study both forward and reverse reaction photodynamics of the recombinant GAF domain of Tlr0924. Primary photoproducts were identified, as were subsequent intermediates at 1 ms. PCB and PVB population photodynamics were decomposed using global target analysis. PCB and PVB populations exhibit similar and parallel photocycles in Tlr0924, but the PVB population exhibits faster excited-state decay in both reaction directions. On the basis of longer time analysis, we show that the photochemical coordinate (15,16-isomerization) and second-linkage coordinate (elimination or bond formation at C10) are separate processes in both directions