The effect of temperature on the internal dynamics of dansylated POPAM dendrimers

The internal and rotational dynamics of the dansylated poly(propylene amine) dendrimers (POPAM) have been studied by time correlated single photon counting (TCSPC) and molecular dynamics (MD) simulations. The hydrodynamic volumes of the dendrimer generations from G1 to G4 were estimated by fluorescence anisotropy data. Experiments and simulations suggest that the volume and the shape of the dendrimers are temperature dependent. At low temperatures the dendrimer structure becomes more spacious and rigid and back-folding of the individual branches is slowed down. For the G3 and G4 generations the temperature effects are much stronger than for the smaller G1 and G2 generations, where back-folding does not play a significant role. MD simulations elucidate the temperature-driven contraction, which is governed by the balance between intra-dendrimer and short-range solvent-dendrimer interactions and is further tuned by the dependence on the dendrimer generation, functionalization, and solvent. These findings pave the way to the design of dendrimers with temperature-dependent volume, accessible area, and host-guest chemistry

THE INFRARED AND RAMAN ROTATION-VIBRATION BAND CONTOURS OF 1,3,5-TRIFLUOROBENZENE-d3d_{3}

$^{1}$ H. F. Shurvell, T. E. Cameron, D. B. Baker, and S. J. Daunt, Spectrochim. Acta (1979), in press.Author Institution:Infrared and Raman band contours of gaseous 1,3,5-trifluorobenzene-$d_{3}$ and Raman band contours of gaseous 1,3,5-trifluorobenzene have been recorded under moderate resolution. First order Coriolis constants have been calculated for the infrared and Raman active $E^{\prime}$ fundamentals using computer simulation of the contours. Coriolis constants of the Raman active $E^{\prime\prime}$ fundamentals are also reported and compared to those predicted in an earlier $study^{1}$. Several infrared overtone and combination bands of $E^{\prime}$ symmetry of the deuterated trifluorobenzene have been simulated and the ``effective’’ Coriolis constants determined. Agreement between observed values of $\zeta^{z}_{eff}$ and the values predicted from $\zeta^{z}_{i}$ constants of the constituent degenerate fundamentals is fairly good. The assignments of the overtone and combination bands of both molecules have been reexamined

Modelling chemical composition in electric systems – implications to the dynamics of dye-sensitised solar cells

Classical electromagnetism provides limited means to model electric generators. To extend the classical theory in this respect, additional information on microscopic processes is required. In semiconductor devices and electrochemical generators such information may be obtained by modelling chemical composition. Here we use this approach for the modelling of dye-sensitised solar cells. We simulate the steady-state current-voltage characteristics of such a cell, as well as its transient response. Dynamic simulations show optoelectronic hysteresis in these cells under transient light pulse illumination

Electron Transfer form Organic Aminophenyl Acid Sensitizers to Titanium Dioxide Nanoparticle Films

none5P. Myllyperkio; C. Manzoni; D. Polli; G. Cerullo; J. Korppi-TommolaP., Myllyperkio; Manzoni, Cristian; Polli, Dario; Cerullo, GIULIO NICOLA; J., Korppi Tommol

Photoinduced interfacial electron injection in RuN3-TiO2 thin films: Resolving picosecond timescale injection from the triplet state of the protonated and deprotonated dyes

Using femtosecond transient absorption spectroscopy we have studied light-induced electron injection from the sensitizer RuN3 and its partly deprotonated tetrabutylamonium salt to nano-structured TiO2 film. Previous studies have suggested significant differences in electron injection dynamics for these dyes and some results have indicated that aggregation of the sensitizer may lead to slow injection. By measuring transient absorption spectra and kinetics of RuN3 and RuN3-TBA in solution and attached to TiO2 film we show that the electron injection dynamics are very similar for the two forms of the dye and that aggregation has only moderate effects on the electron transfer dynamics. (c) 2008 Elsevier B. V. All rights reserved

Interligand electron transfer determines triplet excited state electron injection in RuN3-sensitized TiO2 films

Electron injection from the transition metal complex Ru(dcbpy)(2)(NCS)(2) (dcbpy = 2,2'-bipyridine-4,4'-dicarboxylate) into a titanium dioxide nanoparticle film occurs along two pathways. The dominating part of the electron injection proceeds from the initially excited singlet state of the sensitizer into the conduction band of the semiconductor on the sub-hundred-femtosecond time scale. The slower part of the injection occurs from the thermalized triplet excited state on the picosecond time scale in a nonexponential fashion, as was shown in a previous study (Benko, G.; et al. J. Am. Chem. Soc. 2002, 124, 489). Here we show that the slower channel of injection is the result of the excited state being localized on a ligand of the sensitizer that is not attached to the semiconductor; hence, the electron cannot be injected directly from such an excited state into the semiconductor. Before being injected, it has to be transferred from the non-surface-attached ligand to the attached one. The results show that the interligand electron-transfer time is on the picosecond time scale, depends on the relative energies of the two ligands, and controls the electron injection from the excited triplet state of the sensitizer. The findings provide information relevant to the design of molecular-based assemblies and devices