Circularly‐Polarized Luminescence (CPL) from Chiral AIE Molecules and Macrostructures

Abstract

Circularly-polarized luminescence (CPL) has received new attention on the rise of applications to generate devices and biologically active probes. These applications require fluorophores that are not only chiral but also provide strong fluorescence intensity in aggregated state. Thus, a new research branch has opened up a few years ago, which allows CPL-active fluorophores to be emissive in aggregated-state. As a result, reports on the combination of the CPL property with the aggregation-induced emission (AIE) phenomenon have emerged. Herein the early design principles that have been reported until now to generate CPL-active AIE-active fluorophores (AIEgens) are summarized. In this regard the alignment of monomeric emitters in a chiral fashion, either in supramolecules, polymers or liquid crystals has been proven to be a successful approach. Additionally, first reports have appeared that demonstrate how to tackle the daunting task to furnish individual CPL-active AIEgens.

Circularly Polarized Luminescence from Inorganic Materials: Encapsulating Guest Lanthanide Oxides in Chiral Silica Hosts

“…Optical materials with circularly polarized luminescence (CPL) properties have recently received growing attention as a need to develop not only a powerful spectroscopic tool for structural analysis of chiral systems, but also many applications in optical probes and sensors, advanced microscopies, 3D display, security tags, lasers, data storage, and spin‐optoelectronic circuits . For matching CPL‐active materials, a considerable surge of interest was taken in the design of both chirality and luminescent centres . There are two feasible ways to construct CPL‐active systems.…”

“…One is the chiral arrangement of achiral ligands surrounding the lanthanide ions, the other makes use of chiral ligands with an “antenna” performance . In spite of strong CPL signals being observed in solutions of lanthanide complexes, the solid‐state materials are preferred in many practical CPL‐related applications and especially for high temperature resistance . Unfortunately, the development of solid‐state, chiral lanthanide‐based systems is quite slow so far.…”

Molecular Design, Circularly Polarized Luminescence, and Helical Self‐Assembly of Chiral Aggregation‐Induced Emission Molecules

“…CPL, the emission analog of CD, describes the differential emission of left‐ and right‐handed circularly polarized light of chiral luminescent systems in the excited state. In recent years, CPL‐active functional materials have drawn much attention for their potential applications in biosensing and optoelectronic devices . CPL activity is generally evaluated by the emission dissymmetry factor ( g em ), which is defined as g em =2( I L − I R )/( I L + I R ), where I L and I R are the emission intensities of the left‐ and right‐handed circularly polarized light, respectively.…”

Circularly polarized laser emission in optically active organic dye solutions

“…In particular, organic systems such as molecular dyes or conjugated polymers excel as laser materials across the whole visible spectrum. 16,22 Whereas CPL has been obtained in simple organic molecules, 23 polymers, 3,24,25 and supramolecular assemblies, 26,27 only one CPL emitting system of many has been shown to lase so far, namely, a chiral dibromoBINOL-based substituted O -BODIPY. 28 Unfortunately, its CPL level – comparable to those of similar CPL-simple organic molecules – was far too low to generate a detectable intrinsic CPLE signal.…”

“…In this sense, to have a real (free of optical retardation effects) and detectable CPLE signal, one should move to organic systems with stronger CPL levels by improving their helical (or pseudo -helical) character, and many groups are devoting huge efforts towards this end. 23,26,27 It is expected, though, that the accomplishment of such a goal will necessarily entail stronger levels of OA due to the enhanced helical character. Hence, in the presence of both strong CPL, OA, and LIB, two different effects would contribute to the net CPLE; the “intrinsic” CPLE coming from the amplification of pure CPL, and the “extrinsic” CPLE induced by the combination of OA and LIB.…”