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Reitzenstein D.,University of Würzburg | Quast T.,University of Würzburg | Kanal F.,University of Würzburg | Kullmann M.,University of Würzburg | And 10 more authors.
Chemistry of Materials | Year: 2010

A polyradical consisting of alternating triarylamine and perchlorotriphenylmethyl radical moieties was synthesized by Horner-Emmons reaction. This compound is the first polymeric neutral mixed-valence compound that shows an intervalence charge transfer (IV-CT) band in the NIR. Comparison of the absorption spectra of the polymer with those of a reference monomer shows that the IV-CT transition is confined to one repeating unit. HOMO and LUMO levels are at -5.5 and -4.5 eV vs vacuum, respectively, as estimated by cyclic voltammetry. A very low exciton binding energy is indicated by comparison with the optical band gap (1.2 eV). The electron transfer properties of the polymer were investigated in solution by fs-pump-probe transient absorption spectroscopy. After optical excitation, the polymer shows a biexponential decay in the ps time regime. The short-living, solvent-dependent component refers to the direct decay from the IV-CT state to the ground state and the long-living, solvent-independent component is tentatively attributed to an equilibrium formation of the IV-CT state and a completely charge separated state. The charge-transport properties were investigated in films in organic field-effect transistor (OFET) devices. Electron and hole mobilities are both about 3 × 10 -5 cm 2 V -1 s -1, demonstrating ambipolar transport behavior of the polymer. © 2010 American Chemical Society.


Kaupp M.,TU Berlin | Renz M.,TU Berlin | Parthey M.,TU Berlin | Stolte M.,University of Würzburg | And 5 more authors.
Physical Chemistry Chemical Physics | Year: 2011

This article discusses recent progress by a combination of spectroscopy and quantum-chemical calculations in classifying and characterizing organic mixed-valence systems in terms of their localized vs. delocalized character. A recently developed quantum-chemical protocol based on non-standard hybrid functionals and continuum solvent models is evaluated for an extended set of mixed-valence bis-triarylamine radical cations, augmented by unsymmetrical neutral triarylamine-perchlorotriphenylmethyl radicals. It turns out that the protocol is able to provide a successful assignment to class II or class III Robin-Day behavior and gives quite accurate ground- and excited-state properties for the radical cations. The limits of the protocol are probed by the anthracene-bridged system 8, where it is suspected that specific solute-solvent interactions are important and not covered by the continuum solvent model. Intervalence charge-transfer excitation energies for the neutral unsymmetrical radicals are systematically overestimated, but dipole moments and a number of other properties are obtained accurately by the protocol. © 2011 the Owner Societies.


Heckmann A.,University of Würzburg | Heckmann A.,Wilhelm Conrad Rontgen Research Center for Complex Material Systems | Lambert C.,University of Würzburg | Lambert C.,Wilhelm Conrad Rontgen Research Center for Complex Material Systems
Angewandte Chemie - International Edition | Year: 2012

Mixed-valence (MV) compounds are excellent model systems for the investigation of basic electron-transfer (ET) or charge-transfer (CT) phenomena. These issues are important in complex biophysical processes such as photosynthesis as well as in artificial electronic devices that are based on organic conjugated materials. Organic MV compounds are effective hole-transporting materials in organic light emitting diodes (OLEDs), solar cells, and photochromic windows. However, the importance of organic mixed-valence chemistry should not be seen in terms of the direct applicability of these species but the wealth of knowledge about ET phenomena that has been gained through their study. The great variety of organic redox centers and spacer moieties that may be combined in MV systems as well as the ongoing refinement of ET theories and methods of investigation prompted enormous interest in organic MV compounds in the last decades and show the huge potential of this class of compounds. The goal of this Review is to give an overview of the last decade in organic mixed valence chemistry and to elucidate its impact on modern functional materials chemistry. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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