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Site-Selective Benzannulation of N-Heterocycles in Bidentate Ligands Leads to Blue-Shifted Emission from [(P^N)Cu]2(μ-X)2 Dimers

Mondal, Rajarshi; Lozada, Issiah B.; Davis, Rebecca L.; Williams, J.A. Gareth; Herbert, David E.

Site-Selective Benzannulation of N-Heterocycles in Bidentate Ligands Leads to Blue-Shifted Emission from [(P^N)Cu]2(μ-X)2 Dimers Thumbnail


Authors

Rajarshi Mondal

Issiah B. Lozada

Rebecca L. Davis

David E. Herbert



Abstract

Benzannulated bidentate pyridine/phosphine (P^N) ligands bearing quinoline or phenanthridine (3,4-benzoquinoline) units have been prepared, along with their halide-bridged, dimeric Cu(I) complexes of the form [(P^N)Cu]2(μ-X)2. The copper complexes are phosphorescent in the orange-red region of the spectrum in the solid-state under ambient conditions. Structural characterization in solution and the solid-state reveals a flexible conformational landscape, with both diamond-like and butterfly motifs available to the Cu2X2 cores. Comparing the photophysical properties of complexes of (quinolinyl)phosphine ligands with those of π-extended (phenanthridinyl)phosphines has revealed a counterintuitive impact of site-selective benzannulation. Contrary to conventional assumptions regarding π-extension and a bathochromic shift in the lowest energy absorption maxima, a blue shift of nearly 40 nm in the emission wavelength is observed for the complexes with larger ligand π-systems, which is assigned as phosphorescence on the basis of emission energies and lifetimes. Comparison of the ground-state and triplet excited state structures optimized from DFT and TD-DFT calculations allows attribution of this effect to a greater rigidity for the benzannulated complexes resulting in a higher energy emissive triplet state, rather than significant perturbation of orbital energies. This study reveals that ligand structure can impact photophysical properties for emissive molecules by influencing their structural rigidity, in addition to their electronic structure.

Citation

Mondal, R., Lozada, I. B., Davis, R. L., Williams, J. G., & Herbert, D. E. (2018). Site-Selective Benzannulation of N-Heterocycles in Bidentate Ligands Leads to Blue-Shifted Emission from [(P^N)Cu]2(μ-X)2 Dimers. Inorganic Chemistry, 57(9), 4966-4978. https://doi.org/10.1021/acs.inorgchem.7b03223

Journal Article Type Article
Acceptance Date Apr 4, 2018
Online Publication Date Apr 12, 2018
Publication Date May 7, 2018
Deposit Date May 8, 2018
Publicly Available Date Apr 12, 2019
Journal Inorganic Chemistry
Print ISSN 0020-1669
Electronic ISSN 1520-510X
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 57
Issue 9
Pages 4966-4978
DOI https://doi.org/10.1021/acs.inorgchem.7b03223

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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.7b03223.







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