Quantifying the Overall Efficiency of Circularly Polarized Emitters

Lanthanide ions possess fascinating optical properties and their discovery, first industrial uses and present high technological applications are largely governed by their interaction with light. Lighting devices (economical luminescent lamps, light emitting diodes), television and computer displays, optical fibres, optical amplifiers, lasers, as well as responsive luminescent stains for biomedical analysis, medical diagnosis, and cell imaging rely heavily on lanthanide ions. This critical review has been tailored for a broad audience of chemists, biochemists and materials scientists; the basics of lanthanide photophysics are highlighted together with the synthetic strategies used to insert these ions into mono- and polymetallic molecular edifices. Recent advances in NIR-emitting materials, including liquid crystals, and in the control of luminescent properties in polymetallic assemblies are also presented. (210 references.).

This review summarizes the recent advances in CP-OLEDs based on chiral conjugated polymers, chiral metal complexes, and chiral simple organic molecules. Since the first attempt that was made to obtain direct circularly polarized (CP) light from OLEDs by Meijer et al. in 1997, considerable efforts have been devoted to the development of circularly polarized organic light-emitting diodes (CP-OLEDs), particularly in the recent years. Circularly polarized electroluminescence (CPEL) based on OLEDs has attracted increasing interest for its efficient ability to generate CP light directly and wide potential applications in 3D displays, optical data storage, and optical spintronics. In this review, we systematically summarize the recent progress in chiral emitter based OLEDs with CPEL properties including CPEL based on chiral conjugated polymers, CPEL based on chiral metal complexes, and CPEL based on chiral simple organic molecules, especially chiral thermally activated delayed fluorescence (TADF) molecules. We believe that this review will provide a promising perspective of chiral emitter based OLEDs with CPEL properties for a broad range of scientists in different disciplinary areas and attract a growing number of researchers to this fast-growing research field.

Optical probes that provide information about local chirality have been developed based on changes to the circular polarisation of emitted light. Highly emissive complexes of lanthanide ions are ideally suited for CPL spectroscopy and the design criteria for developing such probes are defined, based on a rigorous stereochemical analysis. The perturbation of a dynamically racemic complex may occur either by a change in complex constitution or by non-covalent association. With complexes of enantiopure ligands, perturbation may involve either dynamic helicity inversion or a reversible change in the lanthanide coordination environment.