Influence of the electron-cation interaction on electron mobility in dye-sensitized ZnO and TiO2 nanocrystals: a study using ultrafast terahertz spectroscopy.

Charge transport and recombination in nanostructured semiconductors are poorly understood key processes in dye-sensitized solar cells. We have employed time-resolved spectroscopies in the terahertz and visible spectral regions supplemented with Monte Carlo simulations to obtain unique information on these processes. Our results show that charge transport in the active solar cell material can be very different from that in nonsensitized semiconductors, due to strong electrostatic interaction between injected electrons and dye cations at the surface of the semiconductor nanoparticle. For ZnO, this leads to formation of an electron-cation complex which causes fast charge recombination and dramatically decreases the electron mobility even after the dissociation of the complex. Sensitized TiO2 does not suffer from this problem due to its high permittivity efficiently screening the charges.

Calculated optoelectronic properties of ruthenium tris-bipyridine dyes containing oligophenyleneethynylene rigid rod linkers in different chemical environments.

Ruthenium tris-bipyridine dyes containing oligophenyleneethynylene (OPE) rigid rod linker groups ([Ru(bpy)3]2+, [Ru(bpy)2bpy-E-Ipa]2+, [Ru(bpy)2bpy-E-Ph-E-Ipa]2+, and [Ru(bpy)2bpy-E-Bco-E-Ipa]2+, where bpy = 2,2'-bipyridine, E = ethynylene, Ph = p-phenylene, Bco = bicyclo[2.2.2]octylene, and Ipa = isophthalic acid) have been investigated using DFT and TD-DFT calculations to elucidate the influence of the rigid rod on their optoelectronic properties. Experimentally observed differences in the optical absorption for the different complexes are discussed on the basis of TD-DFT simulated absorption spectra. A comparison of the calculated optoelectronic properties of [Ru(bpy)2bpy-E-Ph-E-Ipa]2+ in different chemical environments, that is, in different solvents and with or without counter ions, suggests that both the absorption spectra and the redox properties of the dyes with OPE rods are sensitive to the environment. The calculations show that spurious low-energy charge-transfer excitations present in the TD-DFT calculations of the extended systems in vacuum are removed when the environment is included in the calculations.

Copper(I)-catalyzed [2 + 2] photocycloadditions with tethered linkers: synthesis of syn-photodimers of dicyclopentadienes.

Cu(I)-catalyzed intramolecular photocycloadditions of diesters made of endo-dicyclopentadiene derivatives linked by the ester bonds with tethers are highly regio- and stereoselective and complete within hours, and the tethers can be easily cleaved afterward upon reduction with LiAlH4-Irradiation of the diesters afforded a 1:1 mixture of the heretofore unknown exo-cis-exo dimer, originating from the (R,S/S,R) diastereomer of the diester and the exo-trans-exo, deriving from the (R,R/S,S) diastereomer. The intermolecular photodimerization yielded, instead, only exo-trans-exo isomers and side products after irradiation for several days. The role of the tether's length and structure on the course of the photocycloadditions was investigated, and it was observed that short tethers introduce considerable strain in the products' framework. Adamantyl-containing tethers provided the shortest reaction times and highest yields. X-ray diffraction analysis of an exo-cis-exo stereoisomer containing adamantane in the tether exhibited an unusually close approach between H atoms on the methylene bridges and a long C-C distance in the cyclobutane ring. A rearrangement induced by X-ray irradiation was observed in this molecule.