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A BF2 Chelate Exhibiting Excimer-like Fluorescence with an Unusually Large Stokes Shift in the Crystalline Phase

Lookup NU author(s): Dr Ozgur Bozdemir, Dr Owen Woodford, Dr Paul Waddell, Emeritus Professor Anthony Harriman



This is the authors' accepted manuscript of an article that has been published in its final definitive form by John Wiley and Sons Inc, 2023.

For re-use rights please refer to the publisher's terms and conditions.


© 2023 Wiley-VCH GmbH. The target mono-BF2 complex is weakly emissive in fluid solution because radiationless decay of the excited-singlet state is promoted through an intramolecular N⋅⋅⋅H−N hydrogen bond. The lack of mirror symmetry for this compound is attributed to vibronic effects, as reported previously for the bis-BF2 complex (BOPHY). Red-shifted fluorescence is observed from single crystals, the emission quantum yield approaching 30 % with a fluorescence lifetime of 2 ns. The large Stokes shift of 5,700 cm−1 helps minimize self-absorption. Crystallography indicates that the internal fold and twist angles are increased substantially in the crystal, but the hydrogen bond is weakened relative to solution. The crystal structure is compiled from pairs of head-to-tail molecules having a shift of ca. 4.1 Å and closest approach of ca. 3.5 Å. These molecular pairs are arranged in columns, which, in turn, assemble into sheets. The proximity favors excitonic coupling between individual molecules, with the coupling strength obtained by analysis of the absorption spectrum reaching ca. 1,000 cm−1. Both the ideal dipole approximation and the extended dipole methodology seriously overestimate the coupling strength, but the atomic transition charge density procedure leads to good agreement with experiment. Emission is attributed to the closely coupled molecular pair functioning in an excimer-like manner with the exciton trapped in a local minimum. Increasing temperature causes a slight blue shift and loss of fluorescence.

Publication metadata

Author(s): Bozdemir OA, Woodford OJ, Waddell PG, Harriman A

Publication type: Article

Publication status: Published

Journal: Chemistry - A European Journal

Year: 2023

Pages: epub ahead of print

Online publication date: 10/03/2023

Acceptance date: 10/03/2023

Date deposited: 12/05/2023

ISSN (print): 0947-6539

ISSN (electronic): 1521-3765

Publisher: John Wiley and Sons Inc


DOI: 10.1002/chem.202300216

ePrints DOI: 10.57711/kv3a-4b82


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