Advances in circularly polarized luminescence materials based on chiral macrocycles

Chiral Tetrakis Eu(III) Complexes with Ammonium Cations for Improved Circularly Polarized Luminescence

Large dissymmetry factor of the circularly polarized luminescence (gCPL) was observed in ligand and coordination tuned chiral tetrakis europium (Eu(III)) complexes with ammonium cations. The gCPL value was estimated to be -1.54, which is the largest among chiral luminescent molecules. Through photophysical measurements, single crystal X-ray structural analyses and quantum chemical calculations, changes in the geometric and electronic structures were observed for a series of chiral tetrakis Eu(III) complexes which enhanced the gCPL value. The emission quantum yield and photosensitized energy transfer efficiencies of chiral Eu(III) complexes with ammonium cations were also larger than those of chiral Eu(III) complex with Cs+. Based on the systematic modifications and analyses for chiral tetrakis Eu(III) complex, effect of the ammonium cation on enhanced CPL brightness is reported.

Recent Progress in Circularly Polarized Luminescent Materials Based on Cyclodextrins

Circularly polarized luminescence (CPL) materials have been widely used in the fields of bioimaging, optoelectronic devices, and optical communications. The supramolecular interaction, involving harnessing non-covalent interactions between host and guest molecules to control their arrangements and assemblies, represents an advanced approach for facilitating the development of CPL materials and finely constructing and tuning the desired CPL properties. Cyclodextrins (CDs) are cyclic natural polysaccharides, which have also been ubiquitous in various fields such as molecular recognition, drug encapsulation, and catalyst separation. By adjusting the interactions between CDs and guest molecules precisely, composite materials with CPL properties can be facilely generated. This review aims to outline the design strategies and performance of CD-based CPL materials comprehensively and provides a detailed illustration of the interactions between host and guest molecules.

Recent advances in circularly polarized luminescence of planar chiral organic compounds

Circularly polarized luminescence (CPL), as an important chiroptical phenomenon, can not only directly characterize excited-state structural information about chiroptical materials but also has great application prospects in 3D optical displays, information storage, biological probes, CPL lasers and so forth. Recently, chiral organic small molecules with CPL have attracted a lot of research interest because of their excellent luminescence efficiency, clear molecular structures, unique flexibility and easy functionalization. Planar chiral organic compounds make up an important class of chiral organic small molecular materials and often have rigid macrocyclic skeletons, which have important research value in the field of chiral supramolecular chemistry (e.g., chiral self-assembly and chiral host-guest chemistry). Therefore, research into planar chiral organic compounds has become a hotspot for CPL. It is time to summarize the recent developments in CPL-active compounds based on planar chirality. In this feature article, we summarize various types of CPL-active compounds based on planar chirality. Meanwhile, we overview recent research in the field of planar chiral CPL-active compounds in terms of optoelectronic devices, asymmetric catalysis, and chiroptical sensing. Finally, we discuss their future research prospects in the field of CPL-active materials. We hope that this review will be helpful to research work related to planar chiral luminescent materials and promote the development of chiral macrocyclic chemistry.

Structure and Chiroptical Properties of Anthra[1,2-a]anthracene-1-yl Dimers as New Biaryls

Dimers of anthra[1,2-a]anthracene-1-yl units and its mesityl derivative were synthesized by Ni(0)-mediated coupling of the corresponding chloro derivatives as new biaryls. The X-ray analysis and DFT calculations revealed that two polycyclic aromatic units with nonplanar deformations took a twisted conformation about the single bond as a chiral axis. Enantiomers of the nonsubstituted compound were resolved by chiral HPLC, and the enantiopure samples showed intense Cotton effects at 321 nm in the circular dichroism (CD) spectra and emission bands at 449 nm in the circularly polarized luminescence (CPL) spectra with dissymmetry factor of |glum| 3.6×10-3. The absolute stereochemistry of this biaryl was determined by the theoretical calculation of CD spectrum by the time-dependent DFT method. The barrier to enantiomerization was determined to be 108 kJ mol-1 at 298 K. The dynamic process proceeded via a stepwise mechanism involving the helical inversion of each aromatic unit and the rotation about the biaryl axis as analyzed by the DFT calculations.

Strategies for Constructing Macrocyclic Arene-Based Color-Tunable Supramolecular Luminescent Materials

Over the past decades, supramolecular luminescent materials (SLMs) have attracted considerable attention due to their dynamic noncovalent interactions, versatile functions, and intriguing applications in many research fields. From construction to application, great efforts and progress have been made in color-tunable SLMs in recent years. In order to realize multicolor luminescence, various design strategies have been proposed. Macrocyclic chemistry, one of the brightest jewels in the field of supramolecular chemistry, has played a crucial role in the construction of stimuli-responsive and emission-tunable SLMs. Moreover, the flexible and tunable conformation and multiple noncovalent complexation sites of the macrocyclic arenes (MAs) afford a new opportunity to create such dynamic smart luminescent materials. Inspired by our reported work on the color-tunable supramolecular crystalline assemblies modulated by the conformation of naphth[4]arene, this Concept provides a summary of the latest developments in the construction of color-tunable MA-based SLMs, accompanied by the various construction strategies. The aim is to provide researchers with a new perspective to construct color-tunable SLMs with fascinating functions.

Alkoxylated Fluoranthene-Fused [3.3.3]Propellanes: Facile Film Formation against High π-Core Content

Solid-state assembling modes are as crucial as the chemical structures of single molecules for real applications. In this work, solid-state structures and phase-transition temperatures are investigated for a series of fluoranthene-fused [3.3.3]propellanes consisting of a rigid three-dimensional (3D) π-core and varying lengths of alkoxy groups. Compounds in this series with n-butoxy or longer alkoxy groups take an amorphous state at room temperature. In these molecules, rotatable biaryl-type bonds are not incorporated and high D3h molecular symmetry is retained. Therefore, π-fused [3.3.3]propellanes present a unique platform for amorphous molecular materials with low ratios of flexible alkoxy atoms to rigid π-core ones.

A Chirally Locked Bis-perylene Diimide Macrocycle: Consequences for Chiral Self-Assembly and Circularly Polarized Luminescence

Macrocycles containing chiral organic dyes are highly valuable for the development of supramolecular circularly polarized luminescent (CPL) materials, where a preorganized chiral framework is conducive to directing π-π self-assembly and delivering a strong and persistent CPL signal. Here, perylene diimides (PDIs) are an excellent choice for the organic dye component because, alongside their tunable photophysical and self-assembly properties, functionalization of the PDI's core yields a twisted, chiral π-system, capable of CPL. However, configurationally stable PDI-based macrocycles are rare, and those that are also capable of π-π self-assembly beyond dimers are unprecedented, both of which are advantageous for robust self-assembled chiroptical materials. In this work, we report the first bay-connected bis-PDI macrocycle that is configurationally stable (ΔG⧧ > 155 kJ mol-1). We use this chirally locked macrocycle to uncover new knowledge of chiral PDI self-assembly and to perform new quantitative CPL imaging of the resulting single-crystal materials. As such, we discover that the chirality of a 1,7-disubstituted PDI provides a rational route to designing H-, J- and concomitant H- and J-type self-assembled materials, important arrangements for optimizing (chir)optical and charge/energy transport properties. Indeed, we reveal that CPL is amplified in the single crystals of our chiral macrocycle by quantifying the degree of emitted light circular polarization from such materials for the first time using CPL-Laser Scanning Confocal Microscopy.