Ultrafast electron transfer from photoexcited CdSe quantum dots to methylviologen.

The ultrafast charge separation at the quantum dot (QD)/molecular acceptor interface was investigated in terms of acceptor concentration and the size of the QD. Time-resolved experiments revealed that the electron transfer (ET) from the photoexcited QD to the molecular acceptor methylviologen (MV(2+)) occurs on the fs time scale for large acceptor concentrations and that the ET rate is strongly reduced for low concentrations. The increase in the acceptor concentration is accompanied with a growth in the overlap of donor and acceptor wavefunctions, resulting in a faster reaction until the MV(2+) concentration reaches a saturation limit of 0.

Donor/Acceptor adsorbates on the surface of metal oxide nanoporous films: a spectroscopic probe for different electron transfer pathways.

A composite model system which consists of a molecular donor/acceptor pair coupled to the surface of metal oxide nanoporous films is proposed to study the contribution of the surface trap states and their influence on the interfacial ET as well as charge trapping and spatial diffusion processes in films. The photophysics of this donor/acceptor system is investigated by time-resolved transient absorbance spectroscopy in the UV/Vis (347-675 nm) spectral region. Variation of the band gap allows one to disentangle the ET pathways.

Pseudorotation in pyrrolidine: rotational coherence spectroscopy and ab initio calculations of a large amplitude intramolecular motion.

Pseudorotation in the pyrrolidine molecule was studied by means of femtosecond degenerate four-wave mixing spectroscopy both in the gas cell at room temperature and under supersonic expansion. The experimental observations were reproduced by a fitted simulation based on a one-dimensional model for pseudorotation. Of the two conformers, axial and equatorial, the latter was found to be stabilized by about 29 +/- 10 cm(-1) relative to the former one.

Ultrafast charge separation in multiexcited CdSe quantum dots mediated by adsorbed electron acceptors.

Ultrafast ET with a characteristic time constant of approximately 70 fs between CdSe QDs (mean radii of 1.4 nm) photoexcited in the lowest 1S electron state (lambda(exc) = 539 nm), and the molecular electron acceptor MV(2+) adsorbed on the QD surface was observed. The photophysics of such a system was investigated by time-resolved transient absorbance spectroscopy in the UV-visible spectral region.

Ultrafast photoinduced processes in alizarin-sensitized metal oxide mesoporous films.

Close to the edge: Photoexcitation of alizarin coupled to the surface of mesoporous TiO(2) films leads to ultrafast electron transfer to the TiO(2) conduction band (see picture). Complex kinetics after photoexcitation depend on the excitation energy, and indicate a position of the alizarin excited state close to the TiO(2) conduction band edge, where the density of acceptor states is reduced. The photoinduced dynamics in Al(2)O(3) and TiO(2) mesoporous films sensitized by the strongly coupled alizarin dye is investigated by femtosecond transient absorption spectroscopy in the spectral range from UV to mid-IR.

Ultrafast photoinduced dynamics of pigment yellow 101: fluorescence, excited-state intramolecular proton transfer, and isomerization.

The ultrafast excited-state dynamics of the fluorescent pigment yellow 101 (P.Y.101) and the closely related 1,1'-naphthalazine, a nonfluorescent derivative that lacks the OH groups at the naphthyl rings, are studied combining femtosecond spectroscopy and high-level quantum chemical calculations.

Insights into the structure of cyclohexane from femtosecond degenerate four-wave mixing spectroscopy and ab initio calculations.

In this paper, we report the use of femtosecond time-resolved degenerate four-wave mixing rotationally resolved spectroscopy to obtain very accurate structural information on the symmetric top cyclohexane. Apart from highlighting the versatility of this method in determining accurate structures of large and complex molecules without dipole moment, the present study also details the comparison of the experimentally determined rotational constant B(0) with that obtained from high-level ab initio calculations. The theoretical calculations, which were carried out at both the second-order Møller-Plesset (MP2) and coupled-cluster with single, double, and perturbative triple substitutions [CCSD(T)] levels of theory, also take into account vibrational averaging effects.