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Proceedings Paper

Exciton and biexciton signatures in femtosecond transient absorption of pi-conjugated oligomers
Author(s): Victor I. Klimov; Duncan W. McBranch; Nikolay N. Barashkov; John P. Ferraris
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Paper Abstract

We report femtosecond transient-absorption studies of a five-ring oligomer of polyphenylenevinylene prepared in two different forms: as solid-state films and dilute solutions. Both types of samples exhibit a photoinduced absorption (PA) band with dynamics which closely match those of the stimulated emission (SE), demonstrating unambiguously that these features originate from the same species, namely from intrachain singlet excitons. Photochemical degradation of the solid-state samples is demonstrated to dramatically shorten the SE dynamics above a moderate incident pump fluence, whereupon the dynamics of the SE and the long- wavelength PA no longer coincide. In contrast to solutions, solid-state films exhibit an additional short-wavelength PA band with pump-independent dynamics, indicating the efficient formation of non-emissive inter-chain excitons. Correlations in the subpicosecond dynamics of the two PA features, as well as the pump intensity-dependence provide strong evidence that the formation of inter-chain excitons is mediated by intrachain two-exciton states. At high pump levels, we see a clear indication of interaction between excited states also in dilute solutions. This is manifested as a superlinear pump-dependence and shortening of the decay dynamics of the SE. We attribute this behavior to the formation of biexcitons resulting from coherent interaction between two excitons on a single chain.

Paper Details

Date Published: 1 December 1997
PDF: 11 pages
Proc. SPIE 3145, Optical Probes of Conjugated Polymers, (1 December 1997); doi: 10.1117/12.295539
Show Author Affiliations
Victor I. Klimov, Los Alamos National Lab. (United States)
Duncan W. McBranch, Los Alamos National Lab. (United States)
Nikolay N. Barashkov, Univ. of Texas/Dallas (United States)
John P. Ferraris, Univ. of Texas/Dallas (United States)

Published in SPIE Proceedings Vol. 3145:
Optical Probes of Conjugated Polymers
Z. Valy Vardeny; Lewis J. Rothberg, Editor(s)

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