Platinum(ii) complexes of benzannulated N∧N−∧O-amido ligands: bright orange phosphors with long-lived excited states

Lozada, Issiah B.; Williams, J.A. Gareth; Herbert, David E.

Abstract

The synthesis, structural characterization and photophysical properties of a series of platinum(II) complexes of benzannulated pincer-type diarylamido ligands are described. The ligands all contain tricyclic phenanthridine (3,4-benzoquinoline) rings as donor arms, which were elaborated into N∧N−∧O-coordinating β-enaminoketonato chelates via partial condensation with acetylacetone. The proligands are easily deprotonated, and metallation can be achieved under mild conditions using simple Pt(II) salts and Ag2O as a base. The resulting Pt(II) complexes exhibit strong metal-to-ligand charge-transfer absorptions in the region of ∼450–575 nm and are phosphorescent in solution at room temperature, emitting bright orange light (λmax ∼ 600 nm) with quantum yields of up to 16% and excited-state lifetimes on the order of ∼20 μs, representing significant improvements to these photophysical properties compared with many previously reported N∧N∧O or N∧N∧N-ligated systems. Computational modelling reveals that the lowest-lying triplet state is populated efficiently thanks to strong coupling between singlet and triplet excited state manifolds, as in cyclometallated compounds of Pt(II). Substituents (CH3, tBu, or CF3) in the 2-position of the phenanthridinyl unit are found to have little influence on the optical properties, but the emission is severely quenched when a methyl substituent is introduced ortho to the coordinating nitrogen. Molecular distortions in the excited state are shown to be primarily responsible for the quenching in this complex.

Citation

Lozada, I. B., Williams, J. G., & Herbert, D. E. (2022). Platinum(ii) complexes of benzannulated N∧N−∧O-amido ligands: bright orange phosphors with long-lived excited states. Inorganic Chemistry Frontiers, 9(1), 10-22. https://doi.org/10.1039/d1qi01120k

• Journal Article Type: Article
• Acceptance Date: Oct 27, 2021
• Online Publication Date: Oct 27, 2021
• Publication Date: Jan 7, 2022
• Deposit Date: Nov 4, 2021
• Publicly Available Date: Oct 27, 2022
• Journal: Inorganic chemistry frontiers
• Print ISSN: 2052-1553
• Electronic ISSN: 2052-1553
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 9
• Issue: 1
• Pages: 10-22
• DOI: https://doi.org/10.1039/d1qi01120k
• Public URL: https://durham-repository.worktribe.com/output/1225029