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Brightly Luminescent Platinum Complexes of N∧C–∧N Ligands Forming Six-Membered Chelate Rings: Offsetting Deleterious Ring Size Effects Using Site-Selective Benzannulation

Ortiz, Robert J.; Braun, Jason D.; Williams, J.A. Gareth; Herbert, David E.

Brightly Luminescent Platinum Complexes of N∧C–∧N Ligands Forming Six-Membered Chelate Rings: Offsetting Deleterious Ring Size Effects Using Site-Selective Benzannulation Thumbnail


Authors

Robert J. Ortiz

Jason D. Braun

David E. Herbert



Abstract

Brightly emissive platinum(II) complexes (λemission,max = 607–612 nm) of the type RLPtCl are reported, where RL is a cyclometalated N∧C–∧N-coordinating ligand derived from 1,3-di(2-trifluoromethyl-4-phenanthridinyl)benzene (CF3LH) or 1,3-di(2-tert-butyl-4-phenanthridinyl)benzene (tBuLH). Metathesis of the chlorido ligand can be achieved under mild conditions, enabling isolation of ionic compounds with the formula [CF3LPtL′]PF6 where L′ = pyridine or (4-dimethylamino)pyridine (DMAP), as well as the charge-neutral species tBuLPt(C≡C─C6H4─tBu) (C≡C─C6H4─tBu = 4-tert-butylphenylacetylido). Compared with N∧N∧N-ligated Pt(II) complexes that form 5-membered chelates, these compounds all contain 6-membered rings. Expanding the chelate ring size from 5 to 6 has been previously demonstrated to enhance emission in some N∧N∧N-coordinated Pt(II) species─for example, in complexes of 2,6-di(8-quinolinyl)pyridine vs those of 2,2′:6′,2″-terpyridine─but in related N∧C–∧N-coordinated species, luminescence quantum yields are significantly lower for the 6-membered chelate ring complexes. Here, we demonstrate that site-selective benzannulation of the quinolinyl side-arms can offset the deleterious effect of changing the chelate ring-size and boost photophysical properties such as the quantum yield. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations suggest that benzannulation counterintuitively destabilizes the emissive triplet states compared to the smaller π-system, with the “imine-bridged biphenyl” form of the phenanthridinyl arm helping to buffer against larger molecular distortions, enhancing photoluminescence quantum yields up to 0.09 ± 0.02. The spontaneous formation under aerated conditions of a Pt(IV) derivative (CF3LPtCl3) is also reported, together with its molecular structure in the solid state.

Citation

Ortiz, R. J., Braun, J. D., Williams, J. G., & Herbert, D. E. (2021). Brightly Luminescent Platinum Complexes of N∧C–∧N Ligands Forming Six-Membered Chelate Rings: Offsetting Deleterious Ring Size Effects Using Site-Selective Benzannulation. Inorganic Chemistry, https://doi.org/10.1021/acs.inorgchem.1c02551

Journal Article Type Article
Acceptance Date Oct 15, 2021
Online Publication Date Nov 3, 2021
Publication Date 2021
Deposit Date Nov 4, 2021
Publicly Available Date Nov 3, 2022
Journal Inorganic Chemistry
Print ISSN 0020-1669
Electronic ISSN 1520-510X
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
DOI https://doi.org/10.1021/acs.inorgchem.1c02551

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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.1c02551







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