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Fluorescence Emission Anisotropy Coupled to an Electrochemical System:  Study of Exciton Dynamics in Conjugated Polymers

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journal contribution
posted on 13.12.2007, 00:00 by F. Montilla, L. M. Frutos, C. R. Mateo, R. Mallavia
Emission anisotropy studies have been performed for two types of conjugated polymers:  phenylene−vinylene (MDMO−PPV) and fluorene−phenylene (PFP) based polymers. The emission from polymer films deposited onto ITO plates is strongly depolarized due to resonance energy homotransfer in both polymers. This transfer is more efficient for MDMO−PPV than for PFP. The anisotropy of both polymers rises during electrochemical doping. The introduction of randomly distributed quenchers in the conjugated polymer chains decreases the exciton lifetime and therefore the mean free path of each exciton, producing the increase of anisotropy. In addition, green emission bands coming from degraded polyfluorenes have been analyzed by in situ electrochemical polarized fluorescence. The emission from extensively thermal-oxidized polyfluorene is depolarized by exciton transfer between defective fluorenone sites with different orientation of the transition dipole. Conversely, the green emission from electrochemically degraded PFP shows a high polarization degree, suggesting the presence of ordered domains.