Luminescence studies of copper(I)-containing [2]pseudorotaxanes

• Published in: Canadian journal of chemistry Vol. 89; no. 2; pp. 98 - 103
• Main Authors: Briggs, Breeze N, Durola, Fabien, McMillin, David R, Sauvage, Jean-Pierre
• Format: Journal Article
• Language: English
• Published: Ottawa NRC Research Press 01-02-2011; Canadian Science Publishing NRC Research Press
• Subjects: charge transfer; Chemical structure; Copper; Copper compounds; copper(I); cuivre(I); Emissions; Luminescence; Molecular structure; Molecules; Optical properties; rotaxane; Simulation; Stains & staining; Studies; transfert de charge; France
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/V10-093

This report describes photoluminescence studies of copper-containing [2]pseudorotaxanes that mimic elements of functioning molecular machines. Excitation with visible light induces a formal oxidation of the metal center and simulates an actuation process. In all four [2]pseudorotaxanes studied, the ring ligand is the same, but the thread ligand is variable, namely 2,9-di(anisol-4-yl)-1,10-phenanthroline (dap), 6,6′-di(anisol-4-yl)-2,2′-bipyridine (o-dabipy), 5,5′-di(anisol-4-yl)-2,2′-bipyridine (m-dabipy), or 8,8′-di(anisol-4-yl)-3,3′-bi-isoquinoline (dabiiq). The absorbance bandshapes suggest that aryl substituents extending from the core ligands engage in stacking interactions and induce a partially flattened structure in the ground state. More severe flattening occurs in the excited state and precludes the observation of emission if inter-ligand steric forces do not limit the distortion. Thus, the [2]pseudorotaxanes containing dap or o-dabipy as the thread ligand exhibit uncorrected emission maxima at around 720 nm in room-temperature dichloromethane, while the less constrained analogues, containing dabiiq or m-dabipy, are not emissive in fluid solution and barely exhibit a signal in rigid media. In dichloromethane, the luminescence quantum yields of the dap- and o-dabipy-containing systems are 6 × 10
−4
and 4 × 10
−4
, and the excited-state lifetimes are 98 ns and 90 ns, respectively.