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Synthesis and Coordination Chemistry of a Benzannulated Bipyridine: 6,6′-Biphenanthridine

Nemez, Dion B.; Lozada, Issiah B.; Braun, Jason D.; Williams, J.A. Gareth; Herbert, David E.

Synthesis and Coordination Chemistry of a Benzannulated Bipyridine: 6,6′-Biphenanthridine Thumbnail


Authors

Dion B. Nemez

Issiah B. Lozada

Jason D. Braun

David E. Herbert



Abstract

The synthesis, characterization, and coordination chemistry of a doubly π-extended bipyridine analogue, 6,6′-biphenanthridine (biphe), is presented. The structure of the molecule has been determined in the solid state by X-ray diffraction, showing an angle of 72.6° between the phenanthridine planes. The free, uncoordinated organic molecule displays blue fluorescence in solution. It can be singly protonated with strong acids, and the protonated form displays more intense yellow emission. The effect of acid on the excited states is interpreted with the aid of TDDFT calculations. Two Ru(II) coordination complexes, tris(6,6′-biphenanthridine)ruthenium(II) dichloride, [Ru(biphe)3]Cl2, and bis(2,2′-bipyridine)(6,6′-biphenanthridine)ruthenium(II) tetraphenylborate, [Ru(bpy)2(biphe)](BPh4)2, are also reported and their structures determined in the solid state by X-ray diffraction. Both complexes display emission at 77 K that is strongly bathochromically shifted by almost 200 nm compared to that of the archetypal 3MLCT emitter [Ru(bpy)3]2+. Such a red shift is consistent with the more extended conjugation and lower-energy π* orbitals associated with the biphe ligand, lowering the energy of the 3MLCT excited state, as revealed by TDDFT calculations. The efficient non-radiative decay that is typical of such low-energy emitters renders the phosphorescence extremely weak and short-lived at ambient temperature, and rapid ligand photodissociation also competes with radiative decay, especially in the heteroleptic complex. Electrochemical analysis illustrates the effect of biphe’s stabilized vacant π* manifold, with multiple reversible reductions evident at much less negative potentials than those observed for [Ru(bpy)3]2+.

Citation

Nemez, D. B., Lozada, I. B., Braun, J. D., Williams, J. G., & Herbert, D. E. (2022). Synthesis and Coordination Chemistry of a Benzannulated Bipyridine: 6,6′-Biphenanthridine. Inorganic Chemistry, 61(34), 13386-13398. https://doi.org/10.1021/acs.inorgchem.2c01514

Journal Article Type Article
Acceptance Date Aug 1, 2022
Online Publication Date Aug 16, 2022
Publication Date Aug 29, 2022
Deposit Date Aug 16, 2022
Publicly Available Date Aug 17, 2023
Journal Inorganic Chemistry
Print ISSN 0020-1669
Electronic ISSN 1520-510X
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 61
Issue 34
Pages 13386-13398
DOI https://doi.org/10.1021/acs.inorgchem.2c01514
Public URL https://durham-repository.worktribe.com/output/1193760

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Copyright Statement
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.inorgchem.2c01514







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