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Photophysics of Halogenated Fluoresceins: Involvement of Both Intramolecular Electron Transfer and Heavy Atom Effect in the Deactivation of Excited States
Author(s) -
Zhang XianFu,
Zhang Iris,
Liu Lihong
Publication year - 2010
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2010.00706.x
Subject(s) - intersystem crossing , chemistry , xanthene , photochemistry , intramolecular force , quantum yield , excited state , electron transfer , fluorescence , singlet state , electron donor , electron acceptor , moiety , redox , stereochemistry , organic chemistry , atomic physics , catalysis , physics , quantum mechanics
The fluorescence quantum yield (Φ f ), fluorescence lifetime ( τ f ), intersystem crossing quantum yield (Φ isc ) and redox potentials of seven halogenated fluoresceins in their dianion forms were measured and compared in methanol to get a deep insight into the effect of halogeno atoms on their photophysics. It is found that the heavy atom effect alone cannot explain the experimental results, as (1) Φ f for chlorinated dyes exceeds that of fluorescein and close to unity, (2) the sum of Φ f and Φ isc for brominated and iodinated xanthene dyes is remarkably less than unity. The observations can be rationalized by the involvement of intramolecular photoinduced electron transfer, in which the benzoate acts as the electron donor while the xanthene moiety is the acceptor. The more negative reduction potential of excited singlet state for chlorinated fluoresceins results in their much smaller k et , and hence higher Φ f .