doi:10.1016/j.cplett.2006.01.117 
Copyright © 2006 Elsevier B.V. All rights reserved.
Evidence for exciton fission and fusion in a covalently linked tetracene dimer
Astrid M. Müllera, Yuri S. Avlasevichb, Klaus Müllenb and Christopher J. Bardeena, 
, 
aDepartment of Chemistry, University of California Riverside, 501 Big Springs Road, Riverside, CA 92521, United States
bMax Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany
Received 28 September 2005;
revised 13 January 2006.
Available online 3 March 2006.
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Abstract
A photophysical study of the covalently linked tetracene dimer 1,4-bis(tetracen-5-yl)benzene is presented. While the dimer’s steady state spectroscopy is similar to that of monomeric tetracene, it also exhibits a long-lived fluorescence signal in solution and solid polyethylene films, which is absent in the monomer. The behavior of this long-lived component as a function of temperature and oxygenation provides evidence that a small (<1%) fraction of the singlet excited states undergoes fission into two triplet states, which recombine on the order of 100 ns. A kinetic model based on this mechanism fits the fluorescence decay data quantitatively.
Fig. 1. Molecular structure of bistetracene (1,4-bis(tetracen-5-yl)benzene).
Fig. 2. (a) Absorption and (b) steady-state fluorescence spectra of solutions of tetracene (dashed black lines) and bistetracene (solid red lines) in benzene. (For interpretation of the references in colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 3. Time-resolved fluorescence decays of tetracene (black line) and bistetracene (red line) in polyethylene under vacuum at room temperature. (For interpretation of the references in colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 4. (a) Time-resolved fluorescence decays of bistetracene dissolved in degassed (red circles) and oxygenated (black squares) benzene. Also shown is a fit (solid line) to the data taken in degassed benzene with a function that contains the measured Gaussian instrument response convoluted with a biexponential decay. (b) Fluorescence emission spectra of bistetracene in degassed benzene in the 0–20 ns time window (blue) and the 100–300 ns time window (green). (For interpretation of the references in colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. Kinetic scheme for the photophysics of bistetracene. The parameters are defined as follows: S0 = ground singlet state, S1 = excited singlet state which decays by fluorescence (krad), fission into a pair of triplets (kfiss) and intersystem crossing to T1 (kISC), T1 = singly excited triplet state which is formed by ktrip and which cannot reform the S1 state, 2T1 = doubly excited triplet state which is formed by kfiss and recombines back into the S1 state by kfus.
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