Recent advances in the synthesis and applications of macrocyclic arenes.

Macrocyclic arenes including calixarenes, resorcinarenes, cyclotriveratrylene, pillararenes and so on have emerged as highly attractive synthetic macrocyclic hosts due to their unique structures, facile functionalization, and broad range of applications. In recent years, there has been growing interest in the development of novel macrocyclic arenes composed of various aromatic building blocks bridged by methylene groups, which have found applications in various research areas. Consequently, the development of novel macrocyclic arenes has become a frontier and hot topic in supramolecular and macrocyclic chemistry. In this review, we feature the recent advances in the synthesis and applications of novel macrocyclic arenes that have emerged in the last decade. The general synthetic strategies employed for these macrocyclic arenes are systematically summarized, and their wide applications in molecular recognition and assemblies, molecular machines, biomedical science and functional materials are highlighted.

B,N-Embedded Hetero[9]helicene Toward Highly Efficient Circularly Polarized Electroluminescence.

The intrinsic helical π-conjugated skeleton makes helicenes highly promising for circularly polarized electroluminescence (CPEL). Generally, carbon helicenes undergo low external quantum efficiency (EQE), while the incorporation of a multi-resonance thermally activated delayed fluorescence (MR-TADF) BN structure has led to an improvement. However, the reported B,N-embedded helicenes all show low electroluminescence dissymmetry factors (gEL), typically around 1×10-3. Therefore, the development of B,N-embedded helicenes with both a high EQE and gEL value is crucial for achieving highly efficient CPEL. Herein, a facile approach to synthesize B,N-embedded hetero[9]helicenes, BN[9]H, is presented. BN[9]H shows a bright photoluminescence with a maximum at 578 nm with a high luminescence dissymmetry factor (|glum|) up to 5.8×10-3, attributed to its inherited MR-TADF property and intrinsic helical skeleton. Furthermore, circularly polarized OLED devices incorporating BN[9]H as an emitter show a maximum EQE of 35.5 %, a small full width at half-maximum of 48 nm, and, more importantly, a high |gEL| value of 6.2×10-3. The Q-factor (|EQE×gEL|) of CP-OLEDs is determined to be 2.2×10-3, which is the highest among helicene analogues. This work provides a new approach for the synthesis of higher helicenes and paves a new way for the construction of highly efficient CPEL materials.

Macrocycle-Based Charge Transfer Cocrystals with Dynamically Reversible Chiral Self-Sorting Display Chain Length-Selective Vapochromism to Alkyl Ketones.

Chirality-driven self-sorting plays an essential role in controlling the biofunction of biosystems, such as the chiral double-helix structure of DNA from self-recognition by hydrogen bonding. However, achieving precise control over the chiral self-sorted structures and their functional properties for the bioinspired supramolecular systems still remains a challenge, not to mention realizing dynamically reversible regulation. Herein, we report an unprecedented saucer[4]arene-based charge transfer (CT) cocrystal system with dynamically reversible chiral self-sorting synergistically induced by chiral triangular macrocycle and organic vapors. It displays efficient chain length-selective vapochromism toward alkyl ketones due to precise modulation of optical properties by vapor-induced diverse structural transformations. Experimental and theoretical studies reveal that the unique vapochromic behavior is mainly attributed to the formation of homo- or heterochiral self-sorted assemblies with different alkyl ketone guests, which differ dramatically in solid-state superstructures and CT interactions, thus influencing their optical properties. This work highlights the essential role of chiral self-sorting in controlling the functional properties of synthetic supramolecular systems, and the rarely seen controllable chiral self-sorting at the solid-vapor interface deepens the understanding of efficient vapochromic sensors.

Self-Assembled Chiral Polymers Exhibiting Amplified Circularly Polarized Electroluminescence.

Circularly polarized electroluminescence (CPEL) is highly promising in realm of 3D display and optical data storage. However, designing a groundbreaking chiral material with high comprehensive CPEL performance remains a formidable challenge. In this work, a pair of chiral polymers with self-assembled behavior is designed by integrating a chiral BN-moiety into polyfluorene backbone, named R-PBN and S-PBN, respectively. The chiral polymers show narrowband emission centered at 490 nm with full-width half maximum (FWHM) of 29 nm and high photoluminescence quantum yield (PLQY) of 79%. After thermal annealing treatment, the chiral polymers undergo self-assembly, exhibiting amplified circularly polarized luminescence (CPL) with asymmetry factor (|glum|) of up to 0.11. Moreover, the solution-processed nondoped CP-OLEDs based on the chiral polymers as emitting layers exhibit maximum external quantum efficiency (EQEmax) of 9.8%, intense CPEL activities with |gEL| of up to 0.07, and small FWHM of 36 nm, simultaneously. This represents the first case of self-assembled chiral polymers that combines high EQE, large gEL value and narrowband emission.

Single-Molecule White Circularly Polarized Photoluminescence and Electroluminescence from Dual-Emission Enantiomers.

The strategy of integrating conformational isomerization donors and chiral acceptor in single molecule was proposed to construct white circularly polarized luminescence (WCPL) materials in this work. Consequently, a pair of dual-emission enantiomers, namely (R/S)-DO-PTZ, were designed and synthesized, which displayed white emission with blue and yellow dual-emission bands in solution and solid films at Commission Internationale de l'Eclairage (CIE) coordinates of (0.30, 0.33) and (0.33, 0.35), respectively. Meanwhile, (R/S)-DO-PTZ exhibited high PLQY of up to 67% in doped films and obvious mirror-image WCPL signals with |glum| value of 3.0 × 10-3. Moreover, white circularly polarized electroluminescence (WCPEL) based on organic light-emitting diodes (OLEDs) with (R/S)-DO-PTZ as emitters were also achieved with CIE coordinates of (0.32, 0.37) and EQEmax of 4.7%, representing the state-of-the-art level of white OLEDs based on single-molecule purely organic emitters. By optimizing the device structure, warm WCPEL devices were further obtained with |gEL| value of 2.8 × 10-3, CIE coordinates of (0.37, 0.48) and EQEmax of up to 15.6%. To our knowledge, this is the first report of CP-WOLEDs based on single-molecule purely organic emitters.

Naphth[4]arene: Synthesis, Conformations, and Application in Color-Tunable Supramolecular Crystalline Assemblies.

Although the chemistry of macrocyclic arenes has seen rapid development in recent years, the synthesis of new macrocyclic arenes from aromatic rings with no directing groups remains a challenge. In this work, a new macrocyclic arene, naphth[4]arene (NA[4]A), composed of four naphthalene rings bridged by methylene groups, was synthesized using macrocycle-to-macrocycle conversion. NA[4]A shows 1,3-alternate and 1,2-alternate conformations in the solid state, which can be selectively obtained. By supramolecular co-assembly of NA[4]A and 1,2,4,5-tetracyanobenzene (TCNB) in different concentrations and temperatures, two conformation-dependent crystalline luminescent co-assemblies 1,2-NTC and 1,3-NTC can be selectively prepared. Interestingly, the two charge-transfer crystalline assemblies containing NA[4]A with different conformations show bright yellow and green fluorescence, and also display high photoluminescence quantum yields (PLQYs) of 45 % and 43 %. Furthermore, they exhibit color-tunable two-photon excited upconversion emission.

Synthesis of Highly Luminescent Chiral Nanographene.

Chiral nanographenes with both high fluorescence quantum yields (ΦF ) and large dissymmetry factors (glum ) are essential to the development of circularly polarized luminescence (CPL) materials. However, most studies have been focused on the improvement of glum , whereas how to design highly emissive chiral nanographenes is still unclear. In this work, we propose a new design strategy to achieve chiral nanographenes with high ΦF by helical π-extension of strongly luminescent chromophores while maintaining the frontier molecular orbital (FMO) distribution pattern. Chiral nanographene with perylene as the core and two dibenzo[6]helicene fragments as the wings has been synthesized, which exhibits a record high ΦF of 93 % among the reported chiral nanographenes and excellent CPL brightness (BCPL ) of 32 M-1 cm-1 .

TADF-Sensitized Fluorescent Enantiomers: A New Strategy for High-Efficiency Circularly Polarized Electroluminescence.

A promising strategy of thermally activated delayed fluorescence (TADF) sensitized circularly polarized luminescence (CPL) has been proposed for improving the electroluminescence efficiencies of circularly polarized fluorescent emitters. Compared with chiral TADF emitters which suffer from the dilemma of small ΔEST accompanied by small kr , the TADF-sensitized CPL (TSCP) strategy using TADF molecules as sensitizers and CP-FL molecules as emitters might be the most promising method to construct high-performance circularly polarized organic light-emitting diodes (CP-OLEDs). Consequently, by taking advantage of the theoretically 100 % exciton utilization of TADF sensitizers, especially, by designing CP-FL emitters with high PLQY, narrow FWHM and large glum values, TSCP-type CP-OLEDs with excellent overall performances can be realized.

Helic[6]arene-Based Chiral Pseudo[1]rotaxanes and [1]Rotaxanes.

Chiral pseudo[1]rotaxanes and [1]rotaxanes constructed from macrocyclic arenes still remain a big challenge mainly owing to the lack of such chiral macrocycles. In this work, a new system of chiral pseudo[1]rotaxanes formed by self-inclusion of helic[6]arene containing amide linked with the terminal tertiary amines was first discovered. Based on an atom-economic stopping strategy, a pair of chiral [1]rotaxanes were conveniently obtained in almost quantitative yields by blocking the pseudo[1]rotaxanes with monobenzyl bromide of tetraphenylethene. The structures of pseudo[1]rotaxanes and [1]rotaxanes were characterized by 2D NMR spectra in solution, combined with DFT calculations. The photophysical properties further revealed the efficient chirality transfer of helic[6]arene to the tetraphenylethene moiety, compared to their unthreaded chiral isomers. The discovery of the chiral pseudo[1]rotaxanes allows for a wide and available synthesis of chiral [1]rotaxanes, and also opening a new avenue to the design of chiral supramolecular materials.

Linear Axially Chiral Conjugated Polymers Exhibiting Ultralong Low-Temperature Phosphorescence and Intense Circularly Polarized Luminescence.

Ultralong organic phosphorescence (UOP) and circularly polarized luminescence (CPL), as two important branches in the field of organic optical functional materials have broad prospects. In this work, a pair of novel conjugated polymers with low-temperature UOP and intense CPL properties are constructed by incorporating rigid axially chiral chromophores into a polymeric backbone. The twisted and rigid biphenyl skeleton not only effectively reduces the energy gap between the S1 and T to greatly facilitate the intersystem crossing process, but also suppress the non-radiative decay from T1 to S0 . As a result, a strong and ultralong afterglow of up to 33 s is achieved in 2-MeTHF at 77 K. Moreover, the repeating rigid biphenyl skeleton with its helix-like form also promotes the chiroptical activity of the polymers, and intense signals are shown in the low-temperature CPL spectra with absolute glum values of 9.7×10-3 and 5.8×10-3 at the fluorescence and phosphorescence emission peaks, respectively. This work represents the first low-temperature materials with UOP and CPL properties, which provides a new guideline and perspective for the development of persistent luminescence materials.

A Calix[3]acridan-Based Host-Guest Cocrystal Exhibiting Efficient Thermally Activated Delayed Fluorescence.

A supramolecular strategy to construct thermally activated delayed fluorescence (TADF) materials through host-guest charge transfer interactions was proposed. Consequently, a new class of macrocycle namely calix[3]acridan was conveniently synthesized in 90 % yield. The host-guest cocrystal formed by calix[3]acridan and 1,2-dicyanobenzene exhibited efficient TADF properties due to intense intermolecular charge transfer interactions. Moreover, the spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital resulted in a very small singlet-triplet energy gap of 0.014 eV and hence guaranteed an efficient reverse intersystem crossing for TADF. Especially, a high photoluminescence quantum yield of 70 % was achieved, and it represents the highest value among the reported intermolecular donor-acceptor TADF materials.

Enantiomeric Water-Soluble Octopus[3]arenes for Highly Enantioselective Recognition of Chiral Ammonium Salts in Water.

Study of enantioselective recognition in water by synthetic chiral macrocyclic receptors is undoubtedly of theoretical and practical significance, but it is a big challenge to achieve the enantioselective recognition with both high enantioselectivity and high affinity in water probably due to the deficiency of such water-soluble macrocyclic receptors with stable chiral cavities. Herein, we report a new class of chiral macrocyclic arenes named octopus[3]arenes. The enantiomeric macrocycles are composed of three homochiral ethenoanthracene subunits, and they can be synthesized by two pathways and then easily converted into water-soluble octopus[3]arenes P-1 and M-1. Notably, P-1 and M-1 with the rigid hexagonal structures and stable chiral hydrophobic cavities exhibit highly enantioselective recognition towards three pairs of chiral ammonium salts in water with the association constant up to 106  M-1 and the S/R selectivity up to 12.89.

Recent advances on triptycene derivatives in supramolecular and materials chemistry.

Triptycene derivatives, a type of specific aromatic compound, have been attracting much attention in many research areas. Over the past several years, triptycene and its derivatives have been described to be useful and efficient building blocks for the design and synthesis of novel supramolecular acceptors, porous materials and luminescent materials with specific structures and properties. In this review, recent researches on triptycene derivatives in supramolecular and materials chemistry are summarized. Especially, the construction of a new type of macrocyclic arenes and organic cages with triptycene and its derivatives as building blocks are focused on, and their applications in molecular recognition, self-assembly and gas selective sorption are highlighted. Moreover, the applications of triptycene and its derivatives in porous organic materials and thermally activated delayed fluorescence (TADF) materials are also discussed.

Recent advances in circularly polarized electroluminescence based on organic light-emitting diodes.

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.

Synthesis of Chiral Helic[1]triptycene[3]arenes and Their Enantioselective Recognition Towards Chiral Guests Containing Aminoindan Groups.

Starting from the enantiopure precursors, a pair of chiral macrocyclic arenes named helic[1]triptycene[3]arenes were conveniently synthesized. The circular dichroism (CD) spectra of the enantiomeric macrocyclic arenes exhibited mirror images, and the X-ray single crystal structures confirmed their absolute conformations as well. Moreover, the macrocyclic arenes showed strong complexation with secondary ammonium and primary ammonium salts containing aminoindan groups. In particular, the chiral macrocyclic arenes exhibited enantioselective recognition ability towards the chiral secondary ammonium salts containing aminoindan groups with an enantioselective ratio up to 3.89.

Saucer[n]arenes: Synthesis, Structure, Complexation, and Guest-Induced Circularly Polarized Luminescence Property.

Macrocycles denoted as saucer[n]arenes (n=4,5) were easily synthesized by the one-pot condensation of 2,7-dimethoxynaphthalene (2,7-DMN) and paraformaldehyde in the presence of TFA or catalytic BF3 ⋅OEt2 . With 1,1-dimethylpiperidin-1-ium as the template, saucer[4]arene was selectively obtained. Crystal structures show that saucer[n]arenes are all composed of 2,7-DMN moiety bridged by the methylene groups at 1,6-positions: all of the 7-methoxy groups lie on one face, and all of the 2-methoxy groups lie on the other. Saucer[n]arenes exhibit strong fluorescence properties with the quantum yields of 19.6 % and 23.4 %. They form 1:1 complexes with ammonium salts in both solution and solid state (association constant up to 105  M-1 in CDCl3 ). Chiral quaternary ammonium salts can induce the chirality of the dynamically racemic inherently chiral saucer[n]arenes in solution, and thus show mirror-imaged circular dichroism signals and circularly polarized luminescence (CPL) properties.

High-Efficiency Circularly Polarized Electroluminescence from TADF-Sensitized Fluorescent Enantiomers.

A couple of fluorescent enantiomers, which are suitable for the emitters of high-efficiency TADF-sensitized CP-OLEDs, have been developed. The enantiomers show configurational stability, high PLQY of 98 %, large kr of 7.8×107  s-1 , and intense CPL activities with |glum | values of about 2.5×10-3 . Notably, by using matchable TADF sensitizer, the enantiomers were then exploited as emitter to fabricate CP-OLEDs. The TADF-sensitized CP-OLEDs not only show mirror-image CPEL activities with gEL values of +1.8×10-3 and -1.4×10-3 , but also display fast start-up featuring with low VT of 3.0 V as well as driving voltage of 4.8 V at 10 000 cd m-2 . Meaningfully, the TADF-sensitized fluorescent devices show high EQEmax of 21.5 % and extremely low efficiency roll-off, whose EQEs are 21.2 % and 15.3 % at 1000 and 10 000 cd m-2 , respectively. The obtained EQEs are comparable to those of CP-TADF emitters, which provides a promising perspective to break through the EL efficiency limit of CP-FL emitters.

Towards the Highly Efficient Synthesis and Selective Methylation of C(sp3 )-Bridged [6]Cycloparaphenylenes from Fluoren[3]arenes.

An approach to the highly efficient synthesis of C(sp3)-bridged [6]cycloparaphenylenes (C[6]CPPs) from fluoren[3]arenes (F[3]As) was developed. Consequently, F[3]As as a new kind of macrocyclic arenes were synthesized. Followed by the demethylation, triflation and intramolecular aryl-aryl coupling reactions, C[6]CPPs were then conveniently obtained. Interestingly, C[6]CPPs could be selectively methylated to produce their fully outer-methyl-substituted derivatives. The crystal structures showed the hydroxyl-substituted F[3]As had bowl-shaped conformations, and the C[6]CPPs exhibited rigid belt-shaped structures with deep cavities. Moreover, C[6]CPPs exhibited high HOMO energies and narrow energy gaps. An unclosed belt was further obtained, and it not only showed a similar narrow energy gap to those of the aromatic belts, but also displayed strong fluorescence property, which can play a vital role in the design and synthesis of new aromatic belts.

Chiral TADF-Active Polymers for High-Efficiency Circularly Polarized Organic Light-Emitting Diodes.

A strategy of chiral donor-acceptor copolymerization is proposed to develop chiral nonconjugated polymers with thermally activated delayed fluorescence (TADF). Based on this strategy, two pairs of chiral polymers (R,R)-/(S,S)-pTpAcDPS and (R,R)-/(S,S)-pTpAcBP were synthesized. The alternating copolymerization of the chiral donors and acceptors could effectively separate the frontier molecular orbitals, which made the polymers show small ΔEST of 0.01-0.03 eV and efficient TADF properties. Moreover, the polymers also showed the quantum yield of up to 92 % and the circularly polarized luminescence. The solution-processed circularly polarized organic light-emitting diodes showed circularly polarized electroluminescence signals with high external quantum efficiencies of up to 22.1 % and maximum luminance of up to 34350 cd m-2 . This is the first report of CP-OLEDs based on chiral TADF polymer, which provides a useful and valuable guidance for the development of high-efficiency CPEL polymers.

A Green Fluorescent Nitrogen-Doped Aromatic Belt Containing a [6]Cycloparaphenylene Skeleton.

The design and synthesis of nitrogen-doped aromatic belts with conjugated structures still remain a challenge. Here, we report the first nitrogen-doped aromatic belt with a [6]cycloparaphenylene skeleton, which is conveniently synthesized from the easily available calix[3]carbazole. The aromatic belt has a rigid conjugated structure and deep cavity, and it can encapsulate one dichloromethane both in solution and in the solid state. Interestingly, the aromatic belt shows strong green fluorescence with a quantum yield of 0.39 and exhibits a narrow HOMO-LUMO energy gap of 2.02 eV. The belt-shaped conjugated structure composed of three carbazole subunits has specific optoelectronic properties that will promote wide applications in supramolecular chemistry and materials science.