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Titolo:
Relaxation of photo-excitations in films of oligo- and poly(para-phenylenevinylene) derivatives
Autore:
Meskers, SCJ; Janssen, RAJ; Haverkort, JEM; Wolter, JH;
Indirizzi:
Eindhoven Univ Technol, Lab Macromol & Organ Chem, NL-5600 MB Eindhoven, Netherlands Eindhoven Univ Technol Eindhoven Netherlands NL-5600 MB ven, Netherlands Eindhoven Univ Technol, COBRA Interuniv Res Inst, NL-5600 MB Eindhoven, Netherlands Eindhoven Univ Technol Eindhoven Netherlands NL-5600 MB ven, Netherlands
Titolo Testata:
CHEMICAL PHYSICS
fascicolo: 3, volume: 260, anno: 2000,
pagine: 415 - 439
SICI:
0301-0104(20001015)260:3<415:ROPIFO>2.0.ZU;2-R
Fonte:
ISI
Lingua:
ENG
Soggetto:
SITE-SELECTIVE FLUORESCENCE; CONJUGATED POLYMERS; OPTICAL-PROPERTIES; INTERCHAIN INTERACTIONS; SPECTROSCOPY; ABSORPTION; PHOTOLUMINESCENCE; LUMINESCENCE; OLIGOTHIOPHENE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
44
Recensione:
Indirizzi per estratti:
Indirizzo: Meskers, SCJ Univ Marburg, Inst Phys Kern & Makromol Chem, Hans Meerwein Str, D-35032 Marburg, Germany Univ Marburg Hans Meerwein Str Marburg Germany D-35032 rmany
Citazione:
S.C.J. Meskers et al., "Relaxation of photo-excitations in films of oligo- and poly(para-phenylenevinylene) derivatives", CHEM PHYS, 260(3), 2000, pp. 415-439

Abstract

The photo-luminescence from solid films of poly(para-phenylene vinylene) polymers and an oligomeric model system, consisting of seven repeat units, are investigated at low temperature (8 K) using time-resolved spectroscopic techniques. Results are compared to those for the materials in solution. Inthe case of the oligomer, the shape of the visible absorption band observed for the film is quite different from the band shape for the polymer in frozen solution and is characteristic of I-I-type aggregates. Theoretical models are presented describing the dependence of the band shape of absorptionand emission spectra on intermolecular excited state interactions, electron-vibration coupling and disorder represented by distributions of the molecular excitation and intermolecular interaction energies. Using these models, it is concluded that intermolecular interactions in the film of the oligomer are strong (greater than or equal to 1400 cm(-1)), and the disorder low, implying delocalization of the excitation over several molecules. In accordance with these models the fluorescence lifetime for the film (similar to2 ns) is considerably longer than for isolated molecules in solution (0.45ns). The emission spectra of the film, taken early after excitation, are consistent with delocalization of the excitation over several molecules. A time-dependent red shift of the fluorescence band is observed and interpreted in terms of migration of localized excitations between disorder induced trap sites, which exist in the low energy tail of the density of excited states. For the polymers, differences between the shape of the absorption bands of solid film and frozen solution are smaller than for the oligomer indicating that interchain interactions that are, on average, weaker than for the oligomer. For the polymer films, a time-dependent red shift of the emission is observed and fluorescence depolarization measurements provide direct evidence for migration of the photo-excitations between trap sites. For onepolymer, a time dependent change in the band shape of the fluorescence after pulsed excitation is observed with the band shape of the long-lived emission being compatible with that expected for an excitation delocalized overat least two, nearly parallel aligned, chains. For a second polymer, the emission band shape and its time evolution indicate that the major part of the fluorescence originates from disorder induced luminescent sites. These results indicate that the spectroscopic properties of films of pi-conjugatedpolymer critically depend on parameters such as density of defects and excited state interchain interaction energy. (C) 2000 Elsevier Science B.V. All rights reserved.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 01/12/20 alle ore 19:27:35