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...
Resonance in chemical reactions is a very intriguing quantum mechanical phenomenon and provides essential information about the detailed shape of the potential-energy surfaces especially near the nuclear configuration that is critical for dynamical constraints.[1] Fano-type resonance is particularly interesting since it results from the interference of two distinct reactive pathways leading to the same product channel. [2] When an atom is excited to a super-excited state above the ionization threshold energy, and for instance, the isoenergetic continuum is coherently excited at the same time, this results in the interference of direct and indirect ionization processes to give the asymmetric line shape in the ionization cross section.[3] Fano resonance has often been found in the ionization cross section of atoms, whereas its observation in the molecular systems is very rare, especially in gas-phase dynamics. Only a few cases have been reported to date in vibrational autoionization of H 3 [4] or predissociation of H 2 , [5] Cs 2 , [6] and FNO. [7] The multidimensionality of the internal coordinate of polyatomic molecules generally makes the observation of the Fano resonance more difficult since the coherent excitation of bound and continuum states is less probable when the number of internal degrees of freedom increases. The intrinsic spectral congestion of polyatomic molecules may also hamper the experimental observation of asymmetric resonance. Consequently, Fano resonances in polyatomic systems have rarely been interrogated in chemical reactions. Herein, we report the observation of Fano profiles in the partial photodissociation cross section of the diazirine. The yield of the nascent 1 CH 2 (B ) fragment from the S 1 state of diazirine has been monitored as a function of the excitation energy by detecting the total fluorescence emitting in the 1 CH 2 (B ) to 1 CH 2 (ffi) transition. All of the Franck-Condon active bands show asymmetric line shapes, giving the modedependent dynamic parameters, such as homogeneous line width, center of resonance frequency, and the asymmetry parameter. The symmetric and asymmetric C À N stretching modes exhibit quite different Fano profiles, giving qualitative and yet essential information about the shape of the potentialenergy surface in the vicinity of the transition state. Especially since the interference in the reaction pathways could be further utilized to control the outcomes of chemical reactions, [7] the experimental finding of the Fano resonance in a polyatomic molecule may open the possibility of controlling the reaction of complicated molecular systems in multidimensional coordinates through the manipulation of the phase involved in the excitation process.Diazirine (CH 2 N 2 ), as a clean source of carbene and a precursor of diazomethane, [8] has been intensively studied theoretically. However because of the lack of experimental studies, even the structure and dephasing mechanism of diazirine in the first electronically excited state (S 1 ) are still the subject of...
Resonance in chemical reactions is a very intriguing quantum mechanical phenomenon and provides essential information about the detailed shape of the potential-energy surfaces especially near the nuclear configuration that is critical for dynamical constraints. [1] Fano-type resonance is particularly interesting since it results from the interference of two distinct reactive pathways leading to the same product channel. [2] When an atom is excited to a super-excited state above the ionization threshold energy, and for instance, the isoenergetic continuum is coherently excited at the same time, this results in the interference of direct and indirect ionization processes to give the asymmetric line shape in the ionization cross section. [3] Fano resonance has often been found in the ionization cross section of atoms, whereas its observation in the molecular systems is very rare, especially in gas-phase dynamics. Only a few cases have been reported to date in vibrational autoionization of H 3 [4] or predissociation of H 2 , [5] Cs 2 , [6] and FNO. [7] The multidimensionality of the internal coordinate of polyatomic molecules generally makes the observation of the Fano resonance more difficult since the coherent excitation of bound and continuum states is less probable when the number of internal degrees of freedom increases. The intrinsic spectral congestion of polyatomic molecules may also hamper the experimental observation of asymmetric resonance. Consequently, Fano resonances in polyatomic systems have rarely been interrogated in chemical reactions. Herein, we report the observation of Fano profiles in the partial photodissociation cross section of the diazirine. The yield of the nascent 1 CH 2 (B ) fragment from the S 1 state of diazirine has been monitored as a function of the excitation energy by detecting the total fluorescence emitting in the 1 CH 2 (B ) to 1 CH 2 (ffi) transition. All of the Franck-Condon active bands show asymmetric line shapes, giving the modedependent dynamic parameters, such as homogeneous line width, center of resonance frequency, and the asymmetry parameter. The symmetric and asymmetric C À N stretching modes exhibit quite different Fano profiles, giving qualitative and yet essential information about the shape of the potentialenergy surface in the vicinity of the transition state. Especially since the interference in the reaction pathways could be further utilized to control the outcomes of chemical reactions, [7] the experimental finding of the Fano resonance in a polyatomic molecule may open the possibility of controlling the reaction of complicated molecular systems in multidimensional coordinates through the manipulation of the phase involved in the excitation process.Diazirine (CH 2 N 2 ), as a clean source of carbene and a precursor of diazomethane, [8] has been intensively studied theoretically. However because of the lack of experimental studies, even the structure and dephasing mechanism of diazirine in the first electronically excited state (S 1 ) are still the subject o...
The fluorescence excitation (FE) spectrum for the Ã2A2 ↔ X̃2B1 transition of OClO cooled in supersonic jet expansions has been obtained for the first time from the origin band at 476 nm up to 355 nm. Despite rapid predissociation of the excited OClO molecules, the fluorescence emission is strong enough to give the FE spectrum with a high signal-to-noise ratio. The present FE spectrum shows the much lower rotational temperature and hence better state resolution than seen in previously reported spectra, demonstrating that it can be used as a convenient spectroscopic tool for the state and mode selection in the photodissociation dynamics studies. The FE spectroscopy can be also applied for the high-resolution spectroscopy and various kinetic studies on the OClO molecules.
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