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UV-excited aromatic molecules with N–H/O–H moieties often possess an important nonradiative relaxation pathway, from an optically bright ππ* state to a dark dissociative πσ* state. We apply a new time-selected photofragment translational spectroscopy method to disclose a previously unknown triplet-mediated N–H dissociation of aniline prevented by the multiphoton dissociative ionization in conventional methods. We further determined the branching fractions of aniline dissociated in the πσ*, triplet, and ground states at 248 nm. Additionally, we selectively captured the population changes in the singlet and triplet states with ionization from different laser wavelengths, 355 or 266 nm, in time-resolved photoion yields. The combination of experimental data enables us to uniquely determine the relative ionization cross sections of the singlet and triplet states at an ionization laser wavelength of 266 nm and allows us to extensively measure the rate constants of intersystem crossing and the branching fractions at various excitation wavelengths. [ABSTRACT FROM AUTHOR]

Microbial rhodopsins, a diverse group of photoactive proteins found in Archaea, Bacteria, and Eukarya, function in photosensing and photoenergy harvesting and may have been present in the resource-limited early global environment. Four different physiological functions have been identified and characterized for nearly 5,000 retinal-binding photoreceptors, these being ion transporters that transport proton or chloride and sensory rhodopsins that mediate light-attractant and/or -repellent responses. The greatest number of rhodopsins previously observed in a single archaeon had been four. Here, we report a newly discovered six-rhodopsin system in a single archaeon, Haloarcula marismortui, which shows a more diverse absorbance spectral distribution than any previously known rhodopsin system, and, for the first time, two light-driven proton transporters that respond to the same wavelength. All six rhodopsins, the greatest number ever identified in a single archaeon, were first shown to be expressed in H. marismortui, and these were then overexpressed in Escherichia coli. The proteins were purified for absorption spectra and photocycle determination, followed by measurement of ion transportation and phototaxis. The results clearly indicate the existence of a proton transporter system with two isochromatic rhodopsins and a new type of sensory rhodopsin-like transducer in H. marismortui. doi: 10.1128/JB.00642-10

Gold nanotriangles (AuNTs) and nanocubes (NCs) coated with silica shell and fluorescein were synthesized to study the effects of metal‐enhanced fluorescence. The interaction between gold nanoparticles (GNPs) and fluorescein with silica shells of different thicknesses as spacers was investigated by using time‐resolved fluorescence spectroscopy. From the biexponential decay of fluorescence of fluorophore and the kinetic mechanism for the interaction, we obtained the rate constants of energy transfer processes. Both energy transfer rates from fluorophore to the bright and dark modes of gold nanoparticles decreased with distance d (= silica thickness) with a dependence ∝ d−n and n ≈ 2. The rate constant of nanosurface energy transfer kNEST, considering dipolar interaction between fluorophore and metal surface, has an estimated value 1.7 times slower at d = 9 nm and about four times slower at 25 nm than the obtained rate constant for energy transfer from fluorophore to GNP dipolar mode in the AuNT system. For the AuNC system, the rate constants are greater than the AuNT system because of better spectral overlap between emission of fluorescein and surface plasmon resonance. [ABSTRACT FROM AUTHOR]

Photodissociation dynamics of propene at 157.6 nm has been investigated in a molecular beam apparatus using the photofragment translational spectroscopic technique combined with the vacuum ultraviolet ionization method. Eleven photofragments have been successfully detected and ascribed to eight (five binary and three triple) dissociation channels: namely, C[SUB3]H[SUB5] + H, C[SUB3]H[SUB4] + H + H, C[SUB3]H[SUB4] + H[SUB2], C[SUB3]H[SUB3] + H[SUB2] + H, C[SUB2]H[SUB4] + CH[SUB2], C[SUB2]H[SUB3] + CH[SUB3], C[SUB2]H[SUB2] + CH[SUB4], and C[SUB2]H[SUB2] + CH[SUB3] + H. Their branching ratios have been determined to be 1%, 7%, <0.2%, 17%, 6%, 4%, 5%, and 60%, respectively. The complicated multichannel dissociation process has a propensity towards triple dissociations, notably the C[SUB2]H[SUB2] + CH[SUB3] + H channel. In addition, the averaged kinetic energy releases and the fractions in translational energy have also been determined from the measured kinetic energy distributions. For the binary dissociation channels, the fractions in translational energy are less than 18% except the C[SUB3]H[SUB5] + H channel, whereas they are more than 42% for the triple dissociation channels. An intriguing finding indicates that the C[SUB2]H[SUB4] + CH[SUB2] channel has a nearly identical kinetic energy distribution and a similar branching ratio to the C[SUB2]H[SUB3] + CH[SUB3] channel, although the former undergoes a three-center elimination process different from the C-C bond rupture occurring in the latter. [ABSTRACT FROM AUTHOR]

The rate coefficient of the reaction of HSO with O3 at five temperatures in the range 273–423 K was determined by means of the discharge-flow/laser-induced-fluorescence technique. The laser-induced fluorescence of HSO was detected by the gated photon-counting technique; a detection limit ∼4×109 molecules cm-3 was achieved. The reaction was carried out under pseudo-first-order conditions with [O3]>[HSO]; the rate coefficient was determined to be k=(4.7±1.0)×10-14 cm3 molecule-1 s-1 at 298 K, approximately 30% greater than, but within experimental uncertainty of the only previous measurement by Wang and Howard by means of the discharge-flow/laser-magnetic-resonance technique. The temperature dependence of the rate coefficient is expressed in the Arrhenius form, k(T)=(2.1±0.7)×10-12 exp[-(1120±320)/T] cm3 molecule-1 s-1. [ABSTRACT FROM AUTHOR]

The dispersed fluorescence of the A 2A1–X 2E system of CH3O and 13CH3O in a supersonic jet was recorded after excitation of various vibrational levels of the A state. Analysis of the spectra yielded ν2‘ = 1412, ν3‘ = 1047, ν5‘ = 1494, and ν6‘ = 653 cm-1 for the X state of 12CH3O, and ν2‘ = 1408, ν3‘ = 1027, ν5‘ = 1488, and ν6‘ = 649 cm-1 for 13CH3O. The least-squares fitting of the observed 300–306 lines (with spin–orbit splitting removed) yielded ωe=1057±3 cm-1 and ωexe=7.0±0.7 cm-1 for ν3‘ of 12CH3O. Several tentative assignments were also made on the basis of the improved fluorescence spectra. The Fermi-resonant levels 1289 and 1319 cm-1 above v=0 of the A state were also reassigned; the former is better represented as v2’ = 1, whereas the latter is represented as v3’ = 2. [ABSTRACT FROM AUTHOR]

RATIONALE Energy pooling has been suggested as the key process for generating the primary ions during ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI). In previous studies, decreases in fluorescence quantum yields as laser fluence increased for 2-aminobenzoic acid, 2,5-dihydroxybenzoic acid (2,5-DHB), and 3-hydroxypicolinic acid were used as evidence of energy pooling. This work extends the research to other matrices and addresses whether energy pooling is a universal property in UV-MALDI. METHODS Energy pooling was investigated in a time-resolved fluorescence experiment by using a short laser pulse (355 nm, 20 ps pulse width) for excitation and a streak camera (1 ps time resolution) for fluorescence detection. RESULTS The excited-state lifetime of 2,5-DHB decreased with increases in laser fluence. This suggests that a reaction occurs between two excited molecules, and that energy pooling may be one of the possible reactions. However, the excited-state lifetime of 2,4,6-trihydroxyacetophenone (THAP) did not change with increases in laser fluence. The upper limit of the energy pooling rate constant for THAP is estimated to be approximately 100-500 times smaller than that of 2,5-DHB. CONCLUSIONS The small energy pooling rate constant for THAP indicates that the potential contribution of the energy pooling mechanism to the generation of THAP matrix primary ions should be reconsidered. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In dye-sensitized solar cells (DSSCs), the charge recombination at the TiO2/dye/electrolyte interface greatly influences the photoelectron conversion efficiency. Hybrid semiconductor materials with matched band potentials are designed to reduce the charge recombination. In this study, SrTiO3/TiO2 hybridstructure was synthesized by using TiO2 nanoparticles as template in a hydrothermal, showing a negative shift in the flat band potential. The DSSC with the SrTiO3/TiO2 anode exhibits an increased photovoltage and a reduced photocurrent. The suppression of charge recombination at the TiO2/dye/electrolyte interface was observed in the electrochemical impedance spectroscopy, causing an improvement in the photovoltage. However, the SrTiO3/TiO2 system shows an obstructed electrons injection from the dye to SrTiO3/TiO2, limiting the photocurrent performance. The photoelectrochemical properties of the SrTiO3/TiO2 system are discussed in detail herein. [ABSTRACT FROM AUTHOR]