Recently, dye-sensitized solar cells (DSC) have attracted much attention with their low production costs of electricity and relatively high energy-conversion efficiencies. [1][2][3][4] One of the key elements in DSC is the nanoporous TiO 2 electrode, which transfers the electrons from the dye molecules to the transparent conductive-oxide (TCO) electrode and concurrently allows the electrolytes to diffuse to the anchored dyes. Typically, nanoparticles are utilized for the fabrication of the nanoporous TiO 2 layers on the TCO to obtain high surface areas and generate nanopored structures. [1,5,6] In this TiO 2 layer derived from nanoparticles, however, the electrons produced from the dye molecules have to pass through numerous grain boundaries in order to reach the TCO, and the transport of the electrolytes is not efficient due to the irregularity of the pores generated. To this point, the tailoring of TiO 2 nanostructures is a crucial aspect of increasing the current photovoltaic-conversion efficiency of DSC. [7][8][9][10][11][12][13][14][15][16][17][18][19] For the formation of an efficient DSC, a high surface area is prime and essential for the TiO 2 layer to load large amounts of dye molecules that will generate electrons by absorbing sun light. Second, the pores formed in the TiO 2 layer must be sufficiently large in size with excellent mutual connectivity for the efficient diffusion of electrolytes. Third, the defect level and the number of grain boundaries must be minimized to suppress the loss of electrons by recombination or back reaction. In general, however, these factors are not compatible with one another. For example, upon decreasing the size of the TiO 2 nanoparticles, the surface area of the fabricated nanoporous TiO 2 film is increased, and thus more dye molecules can be adsorbed. However, the average pore size is decreased simultaneously, and more defect sites and grain boundaries can be generated in the fabricated TiO 2 film. Therefore, it has been reported that the optimum particle size of TiO 2 has to be in the range of 12-20 nm. [5,6,[20][21][22] In this work, we designed a novel hierarchical pore structure that provides high surface area and large pore size at the same time. That is, nanoporous TiO 2 spheres with high surface area were synthesized and utilized to form the nanoporous TiO 2 electrode. As a result, two kinds of pores were successfully formed in the TiO 2 layer. Tiny internal pores were formed inside the TiO 2 sphere, while large external pores were generated by formation of the interstitial voids among the spherical structures. The large external pores can be used as a ''highway'' for electrolyte diffusion, as shown in Scheme 1. Therefore, it is expected that this porous spherical structure can provide both great adsorption of the dye molecules and efficient electrolyte diffusion at the same time.Sub-micrometer-sized TiO 2 spheres have often been prepared by sol-gel methods controlling the hydrolysis and condensation reactions, and their crystallized structures were formed by su...

No abstract

One- and two-photon fluorescence excitation and emission spectra of the S1↔S0 transition of trans,trans-1,3,5,7-octatetraene have been measured for the first time in free jet expansions. The one-photon excitation spectrum is the same, with the exception of significant differences in the intensities of a few lines, as the two-color, resonance-enhanced, two-photon ionization spectrum, previously assigned to the 2 1A′←1 1A′ transition of cis,trans-1,3,5,7-octatetraene. However, comparison of the one- and two-photon fluorescence excitation spectra shows clearly that the carrier of the spectrum has inversion symmetry, as expected for trans,trans-1,3,5,7-octatetraene. The one-photon spectrum is built on bu Herzberg–Teller promoting modes, which are origins of progressions in ag modes, while the two-photon spectrum is due to a single progression in ag modes starting from the 2 1Ag←1 1Ag electronic origin. The appearance of out-of-plane vibrations, possibly including torsions of the polyene framework, suggests large differences in force constants and perhaps in the geometries of the 2 1Ag and 1 1Ag potential surfaces. For 2 1Ag vibronic levels with energies ≤1000 cm−1, the fluorescence lifetimes vary between 170 and 450 ns due to the dependence of radiative and nonradiative decay rates on the vibronic state. An abrupt increase in the nonradiative decay rates at ∼2100 cm−1 excess energy is tentatively ascribed to trans→cis isomerization. This work demonstrates that the one- and two-photon cross sections of the 2 1Ag←1 1Ag transitions of all-trans linear polyenes are sufficiently large to allow the study of 2 1Ag states under isolated, unperturbed conditions.

RG could be an attractive herbal dietary supplement for relieving menopausal symptoms and conferring favorable effects on markers of cardiovascular disease in postmenopausal women.

No abstract

Quasiclassical trajectory calculations and quantal wave packet calculations for vibrational energy transfer at energies above the dissociation thresholdThe anharmonic mixing of highly excited vibrational states of HFCO above its dissociation threshold is studied by stimulated emission pumping spectroscopy. At 0.05-cm -I resolution, individual molecular eigenstates were resolved and state mixings observed by the distribution of oscillator strength to nearby dark states of the background. Most of the zero-order vibrational levels observed in the energy range between 13 ()()() and 23 ()()() cm -I are assigned to long Franck-Condon-allowed progressions of extremely high overtones of the C-H out-ofplane bending mode (v 6 ) in combination with the C=O stretching mode (v 2 ). The extent of state mixing of highly excited vibrational states is strongly mode dependent. For vibrational states with almost the same total vibrational energy, states with the most quanta in V6 show the least coupling with other states. More strikingly, as the total energy is increased by adding V6 quanta, the state mixing becomes weaker. For the vibrational states observed above 18000 cm -I, those that have all of the energy in v 6 or at most one quantum of excitation in V 2 are extremely stable against state mixing. These appear to be the regular states or quasiperiodic trajectories predicted in some theoretical studies of two-dimensional systems. Extreme motion of the C-H out-of-plane bending mode seems to localize and prevent coupling with other modes.5414

One-and two-photon fluorescence excitation spectra of the S 1 ←S 0 transitions of the all-trans isomers of 1,3,5,7-octatetraene, 1,3,5,7-nonatetraene, and 2,4,6,8-decatetraene have been obtained in free jet expansions. Comparison of the one-and two-photon spectra allows the unambiguous identification of electronic and vibronic origins and, for octatetraene and decatetraene, provides clear evidence for molecular inversion symmetry. One-photon spectra show a g progressions built on Herzberg-Teller, b u promoting modes, while two-photon spectra are built on progressions of a g modes starting from the 2 1 A g ←1 1 A g electronic origins. In nonatetraene, the absence of inversion symmetry results in an allowed electronic origin in both the one-and two-photon spectra. Nevertheless, bands built on vibronic origins dominate the one-photon spectrum. The S 1 ←S 0 spectra of nonatetraene and decatetraene exhibit characteristic splittings of vibronic bands that can be quantitatively explained by the tunneling of the methyl groups through low energy, torsional barriers in the S 1 states. Couplings between methyl torsions and low frequency skeletal modes further complicate the optical spectra. Fluorescence lifetimes indicate abrupt onsets of nonradiative decay processes ͑tentatively attributed to trans→cis isomerization͒ at ϳ2100 cm Ϫ1 excess energy. Systematic differences in the energy dependencies of S 1 nonradiative decays in the three polyenes can be explained by the higher densities of vibronic states in the methyl-substituted compounds.

Long-range ordered cubic mesoporous TiO 2 films with 300 nm thickness were fabricated on fluorine-doped tin oxide (FTO) substrate by evaporation-induced self-assembly (EISA) process using F127 as a structure-directing agent. The prepared mesoporous TiO 2 film (Meso-TiO 2) was applied as an interfacial layer between the nanocrystalline TiO 2 film (NC-TiO 2) and the FTO electrode in the dye-sensitized solar cell (DSSC). The introduction of Meso-TiO 2 increased J sc from 12.3 to 14.5 mA/cm (2), and V oc by 55 mV, whereas there was no appreciable change in the fill factor (FF). As a result, the photovoltaic conversion efficiency ( eta) was improved by 30.0% from 5.77% to 7.48%. Notably, introduction of Meso-TiO 2 increased the transmittance of visible light through the FTO glass by 23% as a result of its excellent antireflective role. Thus the increased transmittance was a key factor in enhancing the photovoltaic conversion efficiency. In addition, the presence of interfacial Meso-TiO 2 provided excellent adhesion between the FTO and main TiO 2 layer, and suppressed the back-transport reaction by blocking direct contact between the electrolyte and FTO electrode.