Rainer Schenk

OPTICAL-SPECTRA AND EXCITATIONS IN PHENYLENE VINYLENE OLIGOMERS

Abstract Experimental results of optical absorption spectra, photoluminescence spectra due to singlet exciton emission and photoinduced absorption spectra due to triplet-triplet transitions of triplet excitons for several oligomers of poly( p -phenylene vinylene) are reported. From the red-shift of the peaks with increasing chain length, the effective conjugation length for long-chain precursor-route samples of the polymer are estimated to be about 10 to 17 repeat units. Theoretical studies, using the valence-effective Hamiltonian (VEH) technique, of the effects of ring torsions upon the electronic properties are also reported. Comparison between absorption and luminescence spectra in solution and in the solid state shows a blue-shift for the solution spectra; this is modelled in terms of a greater degree of ring torsion for these oligomers in solution.

Optical spectra and structure of oligomeric models of polyparaphenylenevinylene

This paper treats the vibrational and UV/visible spectra of oligomers of polyparaphe‐ nylenevinylene (PPV) and lays the background knowledge for the treatment of the spectra and structure of PPV which is treated in the paper that immediately follows. The problem of the molecular conformation of these systems is faced both with MNDO (modified neglect or differential overlap) calculations and with infrared‐Raman experiments. Oligomers are certainly twisted in noncrystalline phases while may approach coplanarity in the solid. Fourier transform Raman spectra are recorded and are interpreted in terms of the recently developed theory of the effective conjugation coordinate.

The charge storage mechanism of conducting polymers: a voltammetric study on defined soluble oligomers of the phenylene–vinylene type

The reductive charging–discharging behaviour of several newly synthesized soluble oligo-p-phenylene-vinylenes was studied by cyclic voltammetry; the results show that both the number of redox states and the magnitude of their energetic interaction depend on the chain length of the corresponding oligomer.

Chain length-dependent polaron (P−) width in phenylenevinylene oligomers: a solid state ENDOR investigation

Abstract We report on the extension of the negative polaron (radical anion) in phenylenevinylene oligomers up to chain length n = 7, where n is the number of phenyl rings. The spin density distribution obtained from solid state pulsed ENDOR spectra is observed to increase with chain length. Local hyperfine interactions as well as the corresponding spin density distribution are reported.

Phonon, pi electron localization and size of the charge carrier in para-phenylenevinylene oligomers and polymer: A spectroscopic study

The vibrational infrared and Raman spectra of a series of t‐butyl substituted oligomers of para‐phenylenevinylene and of the corresponding polymer in the pristine and potassium‐doped states have been recorded for the first time and interpreted on the basis of the theory of the effective conjugation coordinate. The Raman spectra of selectively deuteriated materials have also been analyzed. Evidence is found of strong phonon confinement. The information derived from the spectra is that the charge carrier is confined over a few monomer units and that when the polymer is doped with electron donors the benzene ring is preferentially perturbed. The data collected in this work are compared with the results from UV spectroscopy and ESR experiments which indicate a larger dimension of the charge carrier. The information which can be derived by using in a complementary way the data from these spectroscopies are presented and discussed.

The extension of a polaron (radical anion) over oligophenylenevinylene chains

The radical anions obtained from a homologous series of soluble oligophenylenevinylenes have been characterized by ESR and ENDOR spectroscopy in solution; the spin density tends to be localized in a central unit of the chain.

Multiply charged anions from molecules with extended Π-systems

Abstract Multiply charged anions have been prepared by alkali metal reduction of molecules built from benzene rings joined by vinylene groups. Thus, a tetra(stilbenyl)ethylene can be reduced to an octaanion and a [2 8 ]paracyclophaneoctaene to three different anions, assigned as the tetra-, hexa-, and octaanion, respectively. The hexaanion, a cyclic 54 π-electron system, is diatropic.