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Platinum(II) Complexes of Nonsymmetrical NCN-Coordinating Ligands: Unimolecular and Excimeric Luminescence Properties and Comparison with Symmetrical Analogues

Salthouse, Rebecca J.; Sil, Amit; Gildea, Louise F.; Yufit, Dmitry S.; Williams, J. A. Gareth

Platinum(II) Complexes of Nonsymmetrical NCN-Coordinating Ligands: Unimolecular and Excimeric Luminescence Properties and Comparison with Symmetrical Analogues Thumbnail


Authors

Amit Sil

Louise F. Gildea



Abstract

A series of seven new platinum(II) complexes PtLnCl have been prepared, where Ln is an NCN-coordinating ligand comprising a benzene ring 1,3-disubstituted with two different azaheterocycles. In PtL1–5Cl, one heterocycle is a simple pyridine ring, while the other is an isoquinoline, a quinoline, a pyrimidine (L1, L2, L3), or a p-CF3- or p-OMe-substituted pyridine (L4 and L5). PtL6Cl incorporates both a p-CF3 and a p-OMe-substituted pyridine. The synthesis of the requisite proligands HLn is achieved using Pd-catalyzed cross-coupling methodology. The molecular structures of six of the Pt(II) complexes have been determined by X-ray diffraction. All the complexes are brightly luminescent in deoxygenated solution at room temperature. The absorption and emission properties are compared with those of the corresponding symmetrical complexes featuring two identical heterocycles, PtLnsymCl, and of the parent Pt(dpyb)Cl containing two unsubstituted pyridines [dpybH = 1,3-di(2-pyridyl)benzene]. While the absorption spectra of the nonsymmetrical complexes show features of both PtLnsymCl and Pt(dpyb)Cl, the emission generally resembles that of whichever of the corresponding symmetrical complexes has the lower-energy emission. PtL1Cl differs in that─at room temperature but not at 77 K─it displays emission bands that can be attributed to excited states involving both the pyridine and the isoquinoline rings, despite the latter being unequivocally lower in energy. This unusual behavior is attributed to thermally activated repopulation of the former excited state from the latter, facilitated by the very long-lived nature of the isoquinoline-based excited state. At elevated concentrations, all the complexes show an additional red-shifted emission band attributable to excimers. For PtL1Cl, the excimer strikingly dominates the emission spectra at all but the lowest concentrations (<10–5 M). Trends in the energies of the excimers and their propensity to form are compared with those of the symmetrical analogues.

Citation

Salthouse, R. J., Sil, A., Gildea, L. F., Yufit, D. S., & Williams, J. A. G. (2023). Platinum(II) Complexes of Nonsymmetrical NCN-Coordinating Ligands: Unimolecular and Excimeric Luminescence Properties and Comparison with Symmetrical Analogues. Inorganic Chemistry, 62(31), 12356-12371. https://doi.org/10.1021/acs.inorgchem.3c01439

Journal Article Type Article
Acceptance Date Jun 29, 2023
Online Publication Date Jul 27, 2023
Publication Date Aug 7, 2023
Deposit Date Aug 17, 2023
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 62
Issue 31
Pages 12356-12371
DOI https://doi.org/10.1021/acs.inorgchem.3c01439
Keywords Inorganic Chemistry; Physical and Theoretical Chemistry
Public URL https://durham-repository.worktribe.com/output/1720215

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