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Rapid Intersystem Crossing in Closely‐Spaced but Orthogonal Molecular Dyads
Author(s) -
Harriman Anthony,
Mallon Laura J.,
Ulrich Gilles,
Ziessel Raymond
Publication year - 2007
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200700060
Subject(s) - intersystem crossing , chemistry , bodipy , photochemistry , fluorescence , excited state , pyridine , population , reaction rate constant , protonation , triplet state , molecule , atomic physics , kinetics , ion , optics , physics , demography , organic chemistry , quantum mechanics , sociology , medicinal chemistry , singlet state
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.