The evolution of charge-induced gap states in degenerate and non-degenerate conjugated molecules and polymers as studied by photoelectron spectroscopy
1994 (English)In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 67, no 1, 81-86 p.Article in journal (Refereed) PublishedText
We report the results of ultraviolet photoelectron spectroscopy (UPS) studies of the interaction between sodium and conjugated systems for a series of diphenylpolyees and diffrent oligomers of poly(p-phenylenevinylene) (PPV). The diphenylpolyenes include molecules containing two (i.e., stilbene) to 14 carbon atoms in the polyene part; stilbene itself can also be considered as a phenyl-capped monomer of PPV. Furthermore, a PPV oligomer with three phenylene units, as well as PPV itself, has been studied. The experimental results are interpreted with the help of quantum-chemical calculations using the Hartree-Fock semi-empirical Austin Model 1 (AM1) and valence-effective Hamiltonian (VEH) methods. An important result is that all the systems react strongly with sodium; at high doping levels two new doping-induced states are detected above the valence band edge of the pristine material. In the case of saturation-doped diphenylpolyenes (i.e., two sodiums per molecule), the new states can be discussed in terms of soliton-antisoliton pairs confined within the polyene part of the molecules; in contrast, the self-localized states induced in PPV and its oligomers have to be referred to as bipolarons.
Place, publisher, year, edition, pages
Elsevier, 1994. Vol. 67, no 1, 81-86 p.
Spectroscopy, Conjugated molecules and polymers, Gap states
Chemical Sciences Physical Sciences
IdentifiersURN: urn:nbn:se:liu:diva-124173DOI: 10.1016/0379-6779(94)90015-9ISI: A1994PW12000013OAI: oai:DiVA.org:liu-124173DiVA: diva2:896160
Symposium D on Organic Materials for Electronics - Polymer Interfaces with Metals and Semiconductors, at the 1994 E-MRS Spring Conference, Strasbourg, France, May 24-27, 1994