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Exciplex Formation and Excited State Deactivation of Difluoroborondipyrromethene (Bodipy) Dyads

Lookup NU author(s): Professor Andrew Benniston, Graeme Copley

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Abstract

Two series of geometrically-related dyads are discussed based on the difluoroborondipyrromethene (Bodipy) unit, and incorporating covalently attached hydroquinone/quinone groups. These units are anchored directly, or via a phenylene spacer, to the Bodipy core at the meso position in one series (BD-MHQ, BD-MQ, BD-MPHQ, BD-MPQ), but for the second series the attachment site is the 2-position (BD-SHQ, BD-SQ, BD-SPHQ, BD-SPQ). The compounds show various levels of fluorescence depending on the oxidation state of the appended group and the substitution pattern. In non-polar solvents such as toluene, diethyl ether and dichlorobenzene, the S, state deactivation of the Bodipy unit in BD-SPQ and BD-MPQ is dominated by (1,3)exciplex formation, which has not been reported for Bodipy derivatives so far. In the latter molecule, the decay of the exciplex is divided between population of the Bodipy triplet state (13%-21%) and ground state reformation. This partitioning is not seen for the side-on substituted derivative, BD-SPQ, and only ground state reformation is observed following decay of the exciplex. This difference in behavior is explained by the; radical-pair inter-system-crossing mechanism, which more effectively operates in BD-MPQ because of the orthogonality of the donor-acceptor units. In the more polar solvent CH3CN all the quinone derivatives show fast formation of the charge-separated state (k(CS)) followed by slower charge recombination (k(CR)). The ratio k(CS)/k(CR) <= 80.

Publication metadata

Author(s): Benniston AC, Copley G, Lemmetyinen H, Tkachenko NV

Publication type: Article

Publication status: Published

Journal: ChemPhysChem

Year: 2010

Volume: 11

Issue: 8

Pages: 1685-1692

Print publication date: 01/06/2010

ISSN (print): 1439-4235

ISSN (electronic): 1439-7641

Publisher: Wiley - VCH Verlag GmbH & Co. KGaA

URL: http://dx.doi.org/10.1002/cphc.201000127

DOI: 10.1002/cphc.201000127

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