Universal ultrafast signatures of photoexcitations in conjugated polymers: excitons and charge-transfer polarons

Duncan W. McBranch; Brett Kraabel; Su Xu; Hsing-Lin Wang; Victor I. Klimov

doi:10.1117/12.372706

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17 December 1999 Universal ultrafast signatures of photoexcitations in conjugated polymers: excitons and charge-transfer polarons

Duncan W. McBranch, Brett Kraabel, Su Xu, Hsing-Lin Wang, Victor I. Klimov

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Proceedings Volume 3797, Organic Light-Emitting Materials and Devices III; (1999) https://doi.org/10.1117/12.372706
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1999, Denver, CO, United States

Abstract

Using subpicosecond transient absorption spectroscopy, we have investigated the primary photoexcitations in thin films and solution of several phenylene-based conjugated polymers and an oligomer. We identify two features in the transient absorption spectra and dynamics that are common to all of the materials which we have studied from this family. The first spectral feature is a photoinduced absorption (PA) band peaking near 1 eV which has intensity-dependent dynamics which match the stimulated emission dynamics exactly over two orders of magnitude in excitation density. This band is associated with singlet intrachain excitons. The second spectral feature (observed only in thin films and aggregated solutions) is a PA band peaking near 1.8 eV, which is longer-lived than the 1 eV exciton PA band, and which has dynamics that are independent (or weakly-dependent) on excitation density. This feature is attributed to charge separated (interchain) excitations. These excitations are generated through a bimolecular process. By comparing to samples in which charged excitations are created deliberately by doping with C₆O, we assign these secondary species as bound polarons.

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Duncan W. McBranch, Brett Kraabel, Su Xu, Hsing-Lin Wang, and Victor I. Klimov "Universal ultrafast signatures of photoexcitations in conjugated polymers: excitons and charge-transfer polarons", Proc. SPIE 3797, Organic Light-Emitting Materials and Devices III, (17 December 1999); https://doi.org/10.1117/12.372706

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