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Showing papers by "S. Roth published in 1990"


Journal Article
TL;DR: In this paper, NMR spectroscopic studies and Pariser-Parr Pople (PPP) calculations of donor-acceptor substituted polyenes are reported, and the 13 C chemical shifts were measured and compared with the results from PPP calculations.
Abstract: NMR spectroscopic studies and Pariser-Parr Pople (PPP) calculations of donor-acceptor substituted polyenes are reported. The 13 C chemical shifts were measured and compared with the results from PPP calculations. It was found that the PPP calculations predict the charge distribution in these molecules well, and that during the excitation their dipole moments change from 6D in the ground state to over 30D in the excited state. The strong charge transfer is directly due to the excitation. It occurs mostly on the polyene chain and not on the end groups

1 citations


Book ChapterDOI
01 Jan 1990
TL;DR: In this paper, a technique for probing the underlying physics in a material is the investigation of the behavior of photoexcited states, which are produced by absorption of light, and a wide variety of photo-excitations such as solitons, polarons, bipolarons, and excitons are investigated.
Abstract: A powerful technique for probing the underlying physics in a material is the investigation of the behaviour of photoexcited states, which are produced by absorption of light. Electroactive conjugated polymers exhibit a wide variety of photoexcitations, such as solitons, polarons, bipolarons, and excitons1.

01 Jan 1990
TL;DR: In this paper, the authors describe the Langmuir-Blodgett-technique (LB) method to transfer ordered molecules on the interface water-air and to transfer these ordered films to solid substrates.
Abstract: in molecular electronics1 . They are regarded as molecular wires, which connect other molecular switching elements. If this molecular wire is modified by attaching donor and accep­ tor groups to the ends of the polyene chain, optical excita­ tion of the donor group at a selected photon energy is accom­ panied by a transfer of charge from the donor group to the acceptor group via the polyene chain. In a chemical view this is expressed by shifting the positions of the double-bonds by one c-atom. This optically - induced change of the molecular dipole moment can also be discussed in terms of sOlitons2 . The Langmuir-Blodgett-technique (LB)3 is a method to or­ der molecules on the interface water-air and to transfer these ordered films to solid substrates. Amphiphilic mole­ cules, consisting of a hydrophilic headgroup and a hydrophob­ ic 'tail' are spread on a clean water surface. The molecules lying on the surface form a two-dimensional gas. On reducing the covered surface, the mean area per molecule [A2 /mol] is reduced until the interaction of the molecules induces a phase transition into a liquid-analogous state. This phase transition is characterized by a change of slope in the sur­ face-pressure/area (a/F)-diagram. Further reduction of the phase induces a second transition into 2D-solid state. This face is comparable to a smectic-b phase, all molecules stand­ ing perpendicular to the water surface. In this solid-analo­ gous state the ordered film can be transferred to a solid substrate. The film is held under constant pressure and the