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Luminescent platinum(II) complexes of N^N–^N amido ligands with benzannulated n-heterocyclic donor arms : quinolines offer unexpectedly deeper red phosphorescence than phenanthridines.

Mandapati, Pavan and Braun, Jason D. and Killeen, Charles and Davis, Rebecca L. and Williams, J. A. Gareth and Herbert, David E. (2019) 'Luminescent platinum(II) complexes of N^N–^N amido ligands with benzannulated n-heterocyclic donor arms : quinolines offer unexpectedly deeper red phosphorescence than phenanthridines.', Inorganic chemistry., 58 (21). pp. 14808-14817.

Abstract

A platform for investigating the impact of π-extension in benzannulated, anionic pincer-type N^N–^N-coordinating amido ligands and their Pt(II) complexes is presented. Based on bis(8-quinolinyl)amine, symmetric and asymmetric proligands bearing quinoline or π-extended phenanthridine (3,4-benzoquinoline) units are reported, along with their red-emitting, phosphorescent Pt(II) complexes of the form (N^N–^N)PtCl. Comparing the photophysical properties of complexes of (quinolinyl)amido ligands with those of π-extended (phenanthridinyl)amido analogues revealed a counterintuitive impact of site-selective benzannulation. Contrary to conventional assumptions regarding π-extension, and in contrast to isoenergetic lowest energy absorption bands and a red shift in fluorescence from the organic proligands, a blue shift of nearly 40 nm in the emission wavelength is observed for Pt(II) complexes with more extended bis(phenanthridinyl) ligand π-systems. Comparing the ground state and triplet excited state structures optimized from density functional theory (DFT) and time-dependent-DFT calculations, we trace this effect to a greater rigidity of the benzannulated complexes, resulting in a higher energy emissive triplet state, rather than to a significant perturbation of orbital energies caused by π-extension.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1021/acs.inorgchem.9b02480
Publisher 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.9b02480
Date accepted:09 October 2019
Date deposited:24 October 2019
Date of first online publication:22 October 2019
Date first made open access:22 October 2020

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