Circularly polarized lanthanide luminescence from Langmuir-Blodgett films formed from optically active and amphiphilic EuIII-based self-assembly complexes

Abstract

The development of functional nanomaterials and supramolecular systems is an active area of research, particularly for molecular recognition/sensing, catalysis, optical devices, and magnetically active compounds for switching and data storage. While much attention has been focused on transition-metal-based supramolecular systems, there has been a recent insurgence of lanthanide-based systems. These ions possess rich coordination environments and unique physical properties, such as long-lived and long wavelength emission in the visible or the NIR regions, as well as magnetic properties, which have been exploited for use in the developments of MRI contrast agents. Hence, these properties make them ideal and highly desirable candidates for the formation of functional supramolecular systems. The development of supramolecular assemblies that can be further organized into functional devices is also of great current interest. These assemblies can be achieved by covalently attaching appropriate ligands and complexes to nanoparticles or flat surfaces, through the formation of polymers, or by forming thin films using Langmuir–Blodgett (LB) techniques. Herein we describe our efforts in bridging these two areas of research by employing lanthanide-directed synthesis (using ligands 1 and 2) in the formation of chiral luminescent lanthanide amphiphilic complexes, and their use in the formation of LB films, the properties of which can be probed by using circularly polarized luminescence (CPL). The ligands were designed to include a terdentate coordination pocket with a closely associated sensitizing antenna (i.e. the R- or S-naphthylamine moieties) for the lanthanide ions such as EuIII and TbIII—an approach that has been extremely successful for the development of luminescent supramolecular self-assembly structures, such as chiral “bundles” and dilanthanide triple-stranded helicates. Additionally, a long hydrophobic hexadecyl chain was included to allow the formation of Langmuir–Blodgett films. Ligands 1 and 2 were prepared in yields of 74% and 82%, respectively, by employing EDCI·HCl peptide coupling reactions (EDCI·HCl=1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride) between the R and the S isomers of precursors 3 and 4, respectively, and N-hexadecylamine.

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ORCID for Jonathan A. Kitchen: orcid.org/0000-0002-7139-5666

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