Premium
Opto‐electronic properties of conjugated polymers
Author(s) -
Bässler Heinz
Publication year - 1996
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.19961040123
Subject(s) - photoexcitation , exciton , polydiacetylenes , photoluminescence , excited state , relaxation (psychology) , materials science , chemical physics , molecular physics , excitation , stokes shift , polymer , spectroscopy , conjugated system , atomic physics , electric field , optoelectronics , chemistry , condensed matter physics , physics , luminescence , psychology , social psychology , quantum mechanics , composite material
Abstract There is growing evidence, both theoretical and experimental, that the primary optical excitations in conjugated polymers are of excitonic nature. They are formed instantaneously upon photoexcitation and migrate incoherently among chain segments differing in length and, concomitantly, in excitation energy. Migration is associated with spectral relaxation manifest in the occurrence of a dynamic Stokes shift. Time‐resolved photoluminescence as well as energy transfer studies support this conceptual framework. In systems of the polyphenylenevinylene family the exciton binding energy is estimated to be about 0.4 eV, comparable to that in polydiacetylenes. However, transfer of a charge from an excited chain segment to neighboring chain segments costs less energy. Taking into account that all energy levels are disorder broadened this ensures that a fraction of excitations will find it energetically more favorable to decompose into an electron‐hole pair on adjacent chains (off‐chain or indirect exciton) that acts as precursor for photoconduction. Exciton breaking can be stimulated by a strong electric field as documented by cw and time resolved spectroscopy. Recent fluorescence as well as pump and probe measurements on a ladder type polymer (LPPP) with 150 fs time resolution will be reported which support the above conceptual framework and document the occurrence of stimulated emission.