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Lookup NU author(s): Emeritus Professor Anthony Harriman,
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A borondipyrromethene (bodipy) dye is equipped with a 4-pyridine residue attached via the meso position. The strong fluorescence inherent to this class of dye is extinguished on protonation of the pyridine N atom. For the corresponding N-methylpyridinium derivative, fluorescence from the dye fragment is also extensively quenched due to the onset of a light-induced charge-shift reaction. The resultant charge-transfer state (CTS) is weakly fluorescent and decays primarily by way of population of the triplet excited state localized on the bodipy dye. Time-resolved spectral studies provide rate constants for all the steps involved in the forward and reverse charge-shift reactions. An interesting feature is that the lifetime of the CTS, around 1 ns, correlates with the viscosity of the solvent as might be expected if the rate-limiting step involves a substantial change in geometry. There is an unexpectedly small activation energy for the reverse charge-shift reaction, even allowing for the fact that this involves triplet formation. Local fluorescence is restored on cooling to 77 K. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.
Author(s): Harriman A, Mallon LJ, Ulrich G, Ziessel R
Publication type: Article
Publication status: Published
ISSN (print): 1439-4235
ISSN (electronic): 1439-7641
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