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)(2)bpy-E-Ipa](2+), [Ru(bpy)(2)bpy-E-Ph-E-Ipa](2+), and [Ru(bpy)(2)bpy-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)(2)bpy-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

Meta-substituted Ru(II) rigid rods for sensitization of TiO(2)

Abstract in Undetermined Ruthenium polypyridyl rigid-rod compounds with phenylene-ethynelene (OPE) spacers and an isophthalic acid (Ipa) binding group were synthesized and characterized for sensitization of nanocrystalline TiO(2) (anatase) thin films. Density functional theory predicted that the most stable structure oriented the isophthalic group about 45 degrees from normal to the TiO(2) surface. Comparative experimental studies of meta- and para-isomers revealed small changes in the ground state absorption spectra and very similar excited state and redox properties. The excited state injection yields (inj = 0.15 +/- 0.03)into nanocrystalline TiO(2) and the subsequent charge recombination rates were found to be insensitive to the isomer utilized. Meta-substitution enabled the synthesis of sensitizers with two Ru(II) sensitizers that displayed enhanced sunlight absorption relative to the monomeric compound

Distance dependence of heterogeneous electron transfer probed in ultra high vacuum with femtosecond transient absorption

Electron injection from the excited singlet state of the molecular chromophore perylene into the wide band gap semiconductor TiO2 was investigated in ultra high vacuum employing femtosecond transient absorption fs TA spectroscopy. The chromophores were bound to saturated spacer cum anchor groups. The latter formed bonds on the surface of nm structured anatase TiO2 layers. Both the latter preparation step and the fs TA measurements were performed in a special ultra high vacuum chamber that can accomodate solvents. The rate constants were measured in the so called wide band limiting case where they are controlled only by the electronic coupling strength and not by Franck Condon factors. Measurements with different saturated anchor cum spacer groups revealed an exponential dependence of the rate constants on the reaction distance. The distance parameter was 0.1 nm in ultra high vacuum. The shortest injection time of 13 fs was measured for the carboxyl anchor group and the longest of 4 ps for the long rigid so called tripod anchor cum spacer grou

Femtosecond two photon photoemission probing electron injection from the excited singlet state of perylene attached to a long rigid tripod anchor cum spacer on rutile Ti02 110

Electron injection from the excited singlet state of the molecular chromophore perylene into the rutile single crystal of the wide band gap semiconductor Ti02 was investigated with two photon photoemission 2PPE spectroscopy in ultra high vacuum. The chromophore was attached to the 110 surface via acidic anchors of a tripod spacer cum anchor group. The corresponding wet chemistry preparation step was performed in a special ultra high vacuum chamber that can accomodate solvents. Two electron injection times, i.e., 700 fs and 7 ps, were obtained with about equal weight factors from the fit to the measured time dependent decay of the excited singlet state of the chromophore. UPS and 2PPE data showed the energetic position of the donor state at 0.5 eV above the bottom of the conduction band of rutile 110 . The latter position confirmed the validity of the so called wide band limiting case, where electron transfer is controlled only by the strength of the electronic coupling and not in additioin by Franck Condon factors. The two different injection times were attributed to two different adsorption configurations with two different distances for the chromophore from the crystal surface. A plausible configuration for the largest reaction distance suggests 1 nm distance between the rim of the chromophore and the surface atoms. The latter distance was identified with the 7 ps injection time, whereas the 10 times shorter injection time was attributed to a non identified second adsorption configuration with an about 0.25 nm shorter reaction distanc