Ultrafast photoinduced relaxation dynamics of the indoline dye D149 in organic solvents

The relaxation dynamics of the indoline dye D149, a well-known sensitizer for photoelectrochemical solar cells, have been extensively characterized in various organic solvents by combining results from ultrafast pump–supercontinuum probe (PSCP) spectroscopy, transient UV-pump VIS-probe spectroscopy, time-correlated single-photon counting (TCSPC) measurements as well as steady-state absorption and fluorescence. In the steady-state spectra, the position of the absorption maximum shows only a weak solvent dependence, whereas the fluorescence Stokes shift Δ[small nu, Greek, tilde]F correlates with solvent polarity. Photoexcitation at around 480 nm provides access to the S1 state of D149 which exhibits solvation dynamics on characteristic timescales, as monitored by a red-shift of the stimulated emission and spectral development of the excited-state absorption in the transient PSCP spectra. In all cases, the spectral dynamics can be modeled by a global kinetic analysis using a time-dependent S1spectrum. The lifetime τ1 of the S1 state roughly correlates with polarity [acetonitrile (280 ps) < acetone (540 ps) < THF (720 ps) < chloroform (800 ps)], yet in alcohols it is much shorter [methanol (99 ps) < ethanol (178 ps) < acetonitrile (280 ps)], suggesting an appreciable influence of hydrogen bonding on the dynamics. A minor component with a characteristic time constant in the range 19–30 ps, readily observed in the PSCP spectra of D149 in acetonitrile and THF, is likely due to removal of vibrational excess energy from the S1 state by collisions with solvent molecules. Additional weak fluorescence in the range 390–500 nm is observed upon excitation in the S0 → S2 band, which contains short-lived S2 → S0 emission of D149. Transient absorption signals after excitation at 377.5 nm yield an additional time constant in the subpicosecond range, representing the lifetime of the S2 state. S2 excitation also produces photoproducts

Ultrafast dynamics of the indoline dye D149 on electrodeposited ZnO and sintered ZrO2 and TiO2 thin films

The ultrafast photoinjection and subsequent relaxation steps of the indoline dye D149 were investigated in detail for a mesoporous electrodeposited ZnO thin film and compared with experiments on sintered TiO2 and ZrO2 thin films, all in contact with air, using pump-supercontinuum probe (PSCP) transient absorption spectroscopy in the range 370-770 nm. D149 efficiently injects electrons into the ZnO surface with time constants from ≤70 fs (time-resolution-limited) up to 250 fs, without the presence of slower components. Subsequent spectral dynamics with a time constant of 20 ps and no accompanying change in the oscillator strength are assigned to a transient Stark shift of the electronic absorption spectrum of D149 molecules in the electronic ground state due to the local electric field exerted by the D149 •+ radical cations and conduction band electrons in ZnO. This interpretation is consistent with the shape of the relaxed PSCP spectrum at long times, which resembles the first derivative of the inverted steady-state absorption spectrum of D149. In addition, steady-state difference absorption spectra of D149•+ in solution from spectroelectrochemistry display a bleach band with distinctly different position, because no first-order Stark effect is present in that case. Interference features in the PSCP spectra probably arise from a change of the refractive index of ZnO caused by the injected electrons. The 20 ps component in the PSCP spectra is likely a manifestation of the transition from an initially formed bound D149 •+-electron complex to isolated D149•+ and mobile electrons in the ZnO conduction band (which changes the external electric field experienced by D149) and possibly also reorientational motion of D149 molecules in response to the electric field. We identify additional spectral dynamics on a similar timescale, arising from vibrational relaxation of D149•+ by interactions with ZnO. TiO2 exhibits similar dynamics to ZnO. In the case of ZrO2, electron injection accesses trap states, which exhibit a substantial probability for charge recombination. No Stark shift is observed in this case. In addition, the spectroelectrochemical experiments for D149•+ in dichloromethane and acetonitrile, which cover the spectral range up to 2000 nm, provide for the first time access to its complete D0 → D1 absorption band, with the peak located at 1250 and 1055 nm, respectively. Good agreement is obtained with results from DFT/TDDFT calculations of the D149 •+ spectrum employing the MPW1K functional. © 2012 the Owner Societies

VEGF treatment during status epilepticus alters long-term hippocampal astrocyte morphology: A detailed description of astrocyte morphology and glutamate transporter patterns with and without administration of VEGF and seizure induction

VEGF treatment during pilocarpine-induced status epilepticus (SE) causes enduring preservation of behavioral function in rats in the absence of enduring neuroprotection (Nicoletti et al., 2010). In addition, VEGF treatment reduces hyperexcitability in hippocampal slices without altering neuronal membrane properties (McCloskey et al, 2005). Combined, these data suggest the possibility that other cells or mechanisms could be involved in the beneficial effects of VEGF during SE. Our laboratory is interested in the potential contribution of astrocytes to these effects. Astrocytes are not only reported to contribute to epileptiform discharges in the hippocampus (Tian et al., 2005; Kang et al., 2005) but also to express VEGF receptors (Krum & Rosenstein, 2002). We previously reported that VEGF treatment significantly alters multiple astrocyte parameters such as cell soma size, branching complexity, branch volume, number of dendrites, nodes counts and highest order branching after SE. The current study investigated both astrocyte morphology and glutamate transporter expression one month after SE in animals treated with VEGF or inactivated VEGF during SE. Individual GFAP-immunostained astrocytes from both CA1 and the dentate gyrus hilus were traced using Neurolucida software (Microbrightfield Inc.), allowing morphological parameters to be analyzed via Branched Structure and Sholl analyses. In addition, Image J software was used to measure optical density in GLT1 (glial glutamate transporter 1)-immunostained sections. VEGF treatment during SE significantly prevented post-SE increases in number of branch intersections, process length, and node count. Furthermore, an analysis of the distance to the nearest neighboring astrocyte revealed that VEGF treatment significantly increased inter-astrocyte distance. GLT1 immunoreactivity in VEGF treated animals was decreased compared to seized controls. VEGF treatment did not significantly alter the shape of the astrocytes but rather the branching complexity and size. Because cell morphology impacts cell physiology, it is possible that VEGF\u27s enduring effects on post-SE astrocyte morphology impacts the functioning of the post-seizure hippocampus

Use of Eye Tracking in Cognitive Pretests (Version 1.0)

Cognitive pretesting is generally considered to be indispensable for the successful development of new survey questions, and hence for the quality of the data obtained by the survey. Supplementing cognitive interviewing with the method of eye tracking offers the possibility to observe eye movements of respondents in real-time providing additional information about cognitive processes of respondents. Research suggests that combining both methods helps to identify additional problems with questions that would remain undetected if only one method was applied. This contribution provides an introduction to cognitive interviewing in combination with eye tracking. The following questions are addressed: What is the rationale behind combining cognitive interviewing and eye tracking? How should eye tracking be implemented into cognitive interviewing? How can eye-tracking data be used and analyzed in the context of cognitive pretesting