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

Self-Assembled Pure Covalent Tubes Exhibiting Circularly Polarized Luminescence

Here, we successfully synthesized four structurally analogous, self-assembled chiral molecular tubes with relatively high yields. This achievement involved the condensation of six equivalents of enantiomerically pure trans-cyclohexane-1,2-diamine (trans-CHDA) and three equivalents of the corresponding tetraformyl precursor. Each precursor was equipped with a luminescent linker terminated by two m-phthalaldehyde units. Even though these tetraformyl precursors are barely soluble in almost all organic solvents, the molecular tubes are highly soluble in nonpolar solvents such as chloroform, allowing us to fully characterize them in solution. The stereo-chirality of the chiral bisamino building blocks endows the frameworks of molecular tubes with planar chirality. As a consequence, all of these molecular tubes exhibit circularly polarized luminescence (CPL) with relatively large dissymmetry values |glum| up to 7×10-3, providing an efficient method for synthesizing CPL-active materials.

Handedness-Inverted and Stimuli-Responsive Circularly Polarized Luminescent Nano/Micromaterials Through Pathway-Dependent Chiral Supramolecular Polymorphism

The precise manipulation of supramolecular polymorphs has been widely applied to control the morphologies and functions of self-assemblies, but is rarely utilized for the fabrication of circularly polarized luminescence (CPL) materials with tailored properties. Here, this work reports that an amphiphilic naphthalene-histidine compound (NIHis) readily self-assembled into distinct chiral nanostructures through pathway-dependent supramolecular polymorphism, which shows opposite and multistimuli responsive CPL signals. Specifically, NIHis display assembly-induced CPL from the polymorphic keto tautomer, which become predominant during enol-keto tautomerization shifting controlled by a bulk solvent effect. Interestingly, chiral polymorphs of nanofiber and microbelt with inverted CPL signals can be prepared from the same NIHis monomer in exactly the same solvent compositions and concentrations by only changing the temperature. The tunable CPL performance of the solid microbelts is realized under multi external physical or chemical stimuli including grinding, acid fuming, and heating. In particular, an emission color and CPL on-off switch based on the microbelt polymorph by reversible heating-cooling protocol is developed. This work brings a new approach for developing smart CPL materials via supramolecular polymorphism engineering.

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.

Acceptor Copolymerized Axially Chiral Conjugated Polymers with TADF Properties for Efficient Circularly Polarized Electroluminescence

Chiral conjugated polymer has promoted the development of the efficient circularly polarized electroluminescence (CPEL) device, nevertheless, it remains a challenge to develop chiral polymers with high electroluminescence performance. Herein, by the acceptor copolymerization of axially chiral biphenyl emitting skeleton and benzophenone, a pair of axially chiral conjugated polymers namely R-PAC and S-PAC are synthesized. The target polymers exhibit obvious thermally activated delayed fluorescence (TADF) activities with high photoluminescence quantum yields of 81%. Moreover, the chiral polymers display significant circularly polarized luminescence features, with luminescence dissymmetry factor (|glum|) of nearly 3 × 10-3. By using the chiral polymers as emitters, the corresponding circularly polarized organic light-emitting diodes (CP-OLEDs) exhibit efficient CPEL signals with electroluminescence dissymmetry factor |gEL| of 3.4 × 10-3 and high maximum external quantum efficiency (EQEmax) of 17.8%. Notably, considering both EQEmax and |gEL| comprehensively, the device performance of R-PAC and S-PAC is the best among all the reported CP-OLEDs with chiral conjugated polymers as emitters. This work provides a facile approach to constructing chiral conjugated TADF polymers and discloses the potential of axially chiral conjugated luminescent skeletons in architecting high-performance CP-OLEDs.

Dual Enhancement of Phosphorescence and Circularly Polarized Luminescence through Entropically Driven Self-Assembly of a Platinum(II) Complex

Addressing the dual enhancement of circular polarization (glum) and luminescence quantum yield (QY) in circularly polarized luminescence (CPL) systems poses a significant challenge. In this study, we present an innovative strategy utilizing the entropically driven self-assembly of amphiphilic phosphorescent platinum(II) complexes (L-Pt) with tetraethylene glycol chains, resulting in unique temperature dependencies. The entropically driven self-assembly of L-Pt leads to a synergistic improvement in phosphorescence emission efficiency (QY was amplified from 15 % at 25 °C to 53 % at 60 °C) and chirality, both in the ground state and the excited state (glum value has been magnified from 0.04×10-2 to 0.06) with increasing temperature. Notably, we observed reversible modulation of phosphorescence and chirality observed over at least 10 cycles through successive heating and cooling, highlighting the intelligent control of luminescence and chiroptical properties by regulating intermolecular interactions among neighboring L-Pt molecules. Importantly, the QY and glum of the L-Pt assembly in solid state were measured as 69 % and 0.16 respectively, representing relatively high values compared to most self-assembled CPL systems. This study marks the pioneering demonstration of dual thermo-enhancement of phosphorescence and CPL and provides valuable insights into the thermal effects on high-temperature and switchable CPL materials.

Integration of fine-tuned chiral donor with hybrid long/short-range charge-transfer for high-performance circularly polarized electroluminescence

The synergistic integration of a fine-tuned chiral donor with a hybrid long/short-range charge-transfer mechanism offers an accessible pathway to construct highly efficient circularly polarized emitters. Consequently, a notable dissymmetry factor of 1.6 × 10-3, concomitantly with a record-setting maximum external quantum efficiency of 37.4%, is synchronously realized within a single embodiment.

Liquid-crystalline circularly polarised fluorescent emitters with a high luminescence dissymmetry factor

Chiral liquid-crystalline emitters based on 9,9-dimethyl-10-(4-(phenylsulfonyl)phenyl)-9,10-dihydroacridine and a functionalised binaphthol show smectic liquid crystal phases and circularly polarised blue fluorescence with a high luminescence dissymmetry factor |glum| of 0.13. Solution-processable organic light-emitting diodes (OLEDs) based on the enantiomers were explored.

High-Efficiency Circularly Polarized Light-Emitting Diodes Based on Chiral Metal Nanoclusters

Circularly polarized light-emitting diodes (CP-LEDs) are critical for next-generation optical technologies, ranging from holography to quantum information processing. Currently deployed chiral luminescent materials, with their intricate synthesis and processing and limited efficiency, are the main bottleneck for CP-LEDs. Chiral metal nanoclusters (MNCs) are potential CP-LED materials, given their ease of synthesis and processability as well as diverse structures and excited states. However, their films are usually plagued by inferior electronic quality and aggregation-caused photoluminescence quenching, necessitating their incorporation into host materials; without such a scheme, MNC-based LEDs exhibit external quantum efficiencies (EQEs) < 10%. Herein, we achieve an efficiency leap for both CP-LEDs and cluster-based LEDs by using novel chiral MNCs with aggregation-induced emission enhancement. CP-LEDs using enantiopure MNC films attain EQEs of up to 23.5%. Furthermore, by incorporating host materials, the devices yield record EQEs of up to 36.5% for both CP-LEDs and cluster-based LEDs, along with electroluminescence dissymmetry factors (|gEL|) of around 1.0 × 10-3. These findings open a new avenue for advancing chiral light sources for next-generation optoelectronics.

B-N Covalent Bond Embedded Double Hetero-[n]helicenes for Pure Red Narrowband Circularly Polarized Electroluminescence with High Efficiency and Stability

Chiral B/N embedded multi-resonance (MR) emitters open a new paradigm of circularly polarized (CP) organic light-emitting diodes (OLEDs) owing to their unique narrowband spectra. However, pure-red CP-MR emitters and devices remain exclusive in literature. Herein, by introducing a B-N covalent bond to lower the electron-withdrawing ability of the para-positioned B-π-B motif, the first pair of pure-red double hetero-[n]helicenes (n = 6 and 7) CP-MR emitter peaking 617 nm with a small full-width at half-maximum of 38 nm and a high photoluminescence quantum yield of ≈100% in toluene is developed. The intense mirror-image CP light produced by the enantiomers is characterized by high photoluminescence dissymmetry factors (gPL ) of +1.40/-1.41 × 10-3 from their stable helicenes configuration. The corresponding devices using these enantiomers afford impressive CP electroluminescence dissymmetry factors (gEL ) of +1.91/-1.77 × 10-3 , maximum external quantum efficiencies of 36.6%/34.4% and Commission Internationale de I'Éclairage coordinates of (0.67, 0.33), exactly satisfying the red-color requirement specified by National Television Standards Committee (NTSC) standard. Notably a remarkable long LT95 (operational time to 95% of the initial luminance) of ≈400 h at an initial brightness of 10,000 cd m-2 is also observed for the same device, representing the most stable CP-OLED up to date.

Adjusting the Electron-Withdrawing Ability of Acceptors in Thermally Activated Delayed Fluorescence Conjugated Polymers for High-Performance OLEDs

Constructing high-performance solution-processed organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) conjugated polymers remains a challenging issue. The electron-withdrawing ability of acceptors in TADF units significantly affects the TADF properties of the conjugated polymers. Herein, we have designed three TADF conjugated polymers, in which phenoxazine donors and anthracen-9(10H)-one acceptors are incorporated into the polymeric backbones and side chains, respectively, and the carbazole derivative is copolymerized as the host. By incorporating different heteroatoms, such as nitrogen, oxygen, or sulfur, with slightly different electronegativities into anthracen-9(10H)-one, the effect of the electron-withdrawing ability of the acceptor on the performance of conjugated TADF polymer-based OLEDs is thus systematically studied. It is found that the introduction of a nitrogen atom can enhance the spin-orbital coupling and RISC process due to the modulated energy levels and nature of the excited states. As a result, the solution-processed OLEDs based on the prepared polymer p-PXZ-XN display an excellent comprehensive performance with an EQEmax of 17.6%, a low turn-on voltage of 2.8 V, and a maximum brightness of 14750 cd m-2. Notably, the efficiency roll-off is quite low, maintaining 15.1% at 1000 cd m-2, 12.1% at 3000 cd m-2, and 6.1% at 10000 cd m-2, which ranks in the first tier among the reported TADF conjugated polymers. This work provides a guideline for constructing high-efficiency TADF polymers.

Time-Dependent Colorful Circularly Polarized Organic Ultralong Room Temperature Phosphorescence from a Single-Component Chiral Molecule

Colorful circularly polarized organic ultralong room temperature phosphorescence (CP-OURTP) materials have attracted much attention due to their superior optoelectronic properties for various applications. However, the development of colorful CP-OURTP materials in a single-component molecular system is currently facing great challenges. Herein, a feasible strategy is proposed to develop colorful CP-OURTP material from a single-component chiral molecule by introducing a chiral unit into the phosphorescence chromophore. A dual CP-OURTP band originated from inherent triplet excitons emission showing a lifetime of 946.44 ms and triplet-triplet annihilation induced delayed emission with a short lifetime of 209.91 ms as well as maximum asymmetry factors of ≈10-3 are realized. Owing to the changed OURTP intensity ratios between inherent CP-OURTP and delayed emission at different delayed times, time-dependent colorful CP-OURTP turned from yellow to green is obtained. This study provides a potential platform to prepare circularly polarized material systems showing colorful luminescent properties.

Single Molecular Persistent Room-Temperature Phosphorescence and Circularly Polarized Luminescence from Binaphthol-Decorated Optically Innocent Cyclotriphosphazenes

Circularly polarized luminescence (CPL) features of BINOL-decorated cyclotriphosphazenes (CPs) are reported for the first time. The luminescence dissymmetry factor (glum ) of these compounds in chloroform solutions and polymethyl methacrylate (PMMA) thin films with wt 1 % doping concentrations are found to be 1.0×10-3 , and 2.9×10-3 , respectively. However, no CPL signal is observed for the pristine solids. The enantiomers (CP-(R)/CP-(S)) show ultraviolet photoluminescence (~350-360 nm) in solution and the solid state. These compounds show ~10 times larger absolute photoluminescence quantum yield (PLQY) than the simple BINOLs in the solutions state. In the solid state, CP-(R) shows larger PLQY than binaphthol-(R); in contrast, the S enantiomer shows lower PLQY than binaphthol-(S); this indicates that the isomer-dependent solid-state packing of these compounds plays a crucial role in controlling the PL. Thin films with more than 1 % doping concentration and pristine solids of these compounds do not show persistent room-temperature phosphorescence (pRTP) due to concentration-caused quenching. However, thin films with wt 1 % of these chiral emitters exhibit pRTP characteristics with a ~159-343 ms lifetime under vacuum. Theoretical calculations reveal that the cyclophosphazene acts as an optically innocent dendritic core, and the optical features of these compounds are dictated by the pendent BINOL chromophore.

Chemical resolution of spiroindanones and synthesis of chiroptical polymers with circularly polarized luminescence

Herein, the synthesis and chemical resolution of 1,1'-spirobisindane-3,3'-dione have been accomplished utilizing inexpensive and readily available benzaldehyde and acetone as starting materials, and (1R,2R)- or (1S,2S)-1,2-diphenylethane-1,2-diol as a recyclable chiral resolution reagent. The further transformation of R- and S-1,1'-spirobisindane-3,3'-dione into chiral monomers and polymers has been achieved by the reasonable design of the synthetic route and the optimization of the polymerization conditions. The resulting chiroptical polymers exhibit blue emission with thermally activated delayed fluorescence (TADF), excellent optical activities with circular dichroism intensities per molar absorption coefficient (g_abs) of up to 6.4 × 10^-3, and intense circularly polarized luminescence (CPL) with luminescence dissymmetry factor (g_lum) values of up to 2.4 × 10^-3.

Porous Triptycene Network Based on Tröger's Base for CO2 Capture and Iodine Enrichment

A three-dimensional rigid "six-connected" porous triptycene network based on Tröger's base (TB-PTN) was synthesized by using triptycenes as connectors and Tröger's base as linkers. With characteristics of a high surface area of 1528 m² g^-1, nitrogen-enriched groups, and superior thermal stability, TB-PTN displays a high CO₂ uptake of 22.3 wt % (273 K, 1 bar) and excellent iodine vapor adsorption (240 wt %).

Delayed luminescence guided enhanced circularly polarized emission in atomically precise copper nanoclusters

Metal nanoclusters, owing to their intriguing optical properties, have captivated research interest over the years. Of special interest have been chiral nanoclusters that display optical activity in the visible region of the electromagnetic spectrum. While the ground state chiral properties of metal nanoclusters have been reasonably well studied, of late research focus has shifted attention to their excited state chiral investigations. Herein, we report the synthesis and chiral investigations of a pair of enantiomerically pure copper nanoclusters that exhibit intense optical activity, both in their ground and excited states. The synthesis of nanoclusters using l- and d-isomers of the chiral ligand led to the formation of metal clusters that displayed mirror image circular dichroism and circularly polarized luminescence signals. Structural validation using single crystal XRD, powder XRD and XPS in conjunction with chiroptical and computational analysis helped to develop a structure-property correlation that is unique to such clusters. Investigations on the mechanism of photoluminescence revealed that the system exhibits long excited state lifetimes. A combination of delayed luminescence and chirality resulted in circularly polarized delayed luminescence, a phenomenon that is rather uncommon to the field of metal clusters. The chiral emissive properties could be successfully demonstrated in free-standing polymeric films highlighting their potential for use in the field of data encryption, security tags and polarized light emitting devices. Moreover, the fundamental understanding of the mechanism of excited state chirality in copper clusters opens avenues for the exploration of similar effects in a variety of other clusters.

Efficient Red-Emissive Circularly Polarized Electroluminescence Enabled by Quasi-2D Perovskite with Chiral Spacer Cation

Perovskites are promising environmentally sustainable materials for circularly polarized electroluminescence (CPEL). While another chiral nonemissive layer is required for the developed perovskite-based CPEL, we report herein a highly efficient circularly polarized electroluminescence based on a single layer of quasi-2D perovskite with achiral phenethylammonium iodide (PEAI) and chiral S/R-1-(1-naphthyl)ethylammonium iodide (S/R-NEAI) as dual spacer cations. The quasi-2D perovskite was further passivated by carbazole-functionalized phosphonium. The as-fabricated film exhibits not only a circular dichroism (CD) signal but also prominent circularly polarized luminescence (CPL) activity with a maximum photoluminescence dissymmetry factor (g_lum) of ∼2.1 × 10^-3. More importantly, a highly efficient, spin-polarized light-emitting diode (LED) was fabricated based on the in situ passivated quasi-2D perovskite with a peak external quantum efficiency of 3.7% and a maximum electroluminescence dissymmetry factor (g_EL) of ∼4.0 × 10^-3.

Recent Progress in Research on [2.2]Paracyclophane-Based Dyes

In recent years, the [2.2]paracyclophane (PCP) ring has attracted extensive attention due to its features of providing not only chirality and electron-donating ability but also steric hindrance, which reduces intermolecular π-π stacking interactions and thereby improves the fluorescence properties of dyes. To date, some circularly polarized luminescence (CPL)-active small organic molecules based on the PCP skeleton have been reviewed; however, the application of the PCP ring in improving the photophysical properties of fluorescent dyes is still limited, and new molecular design strategies are still required. This review summarizes and promotes the application of PCP in fluorescent dye design, fluorescence detection, and CPL modulation. We expect that this review will provide readers with a comprehensive understanding of the PCP skeleton and lead to further improvement in fluorescent dye design.

Impact of chiral ligands on photophysical and electro-optical properties of β-diketonate europium complexes in circularly polarized OLEDs

Luminescent lanthanide complexes exhibiting chiroptical properties are attracting attention for their application in chiral optoelectronics and photonics, thanks to their unique optical properties, allied to intraconfigurational f-f transitions, which are generally electric-dipole-forbidden and can be magnetic dipole-allowed, which in an appropriate environment can lead to high dissymmetry factors and strong luminescence, in the presence of an antenna ligand. However, because luminescence and chiroptical activity are governed by different selection rules, their successful application in commonly used technologies is still an expectation. Recently, we showed that europium complexes bearing β-diketonates acting as luminescence sensitizers, and chiral bis(oxazolinyl) pyridine derivatives as the chirality inducer, reasonably perform in circularly polarized (CP) organic light-emitting devices (OLEDs). Indeed, europium β-diketonate complexes are an interesting molecular starting point, given their strong luminescence and their established use in conventional (i.e., nonpolarized) OLEDs. In this context, it is interesting to investigate in detail the impact of the ancillary chiral ligand on complex emission properties and the performances of corresponding CP-OLEDs. Here we show that, by incorporating the chiral compound as emitter in the architecture of solution processed electroluminescent devices, CP emission is retained, and the efficiency of the device is comparable to reference unpolarized OLED. The observed remarkable dissymmetry values strengthen the position of chiral lanthanide-OLEDs as CP-emitting devices.

Planar Chiral Multiple Resonance Thermally Activated Delayed Fluorescence Materials for Efficient Circularly Polarized Electroluminescence

Chiral boron/nitrogen doped multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters are promising for highly efficient and color-pure circularly polarized organic light-emitting diodes (CP-OLEDs). Herein, we report two pairs of MR-TADF materials (Czp-tBuCzB, Czp-POAB) based on planar chiral paracyclophane with photoluminescence quantum yields of up to 98 %. The enantiomers showed symmetric circularly polarized photoluminescence spectra with dissymmetry factors |g_PL | of up to 1.6×10^-3 in doped films. Meanwhile, the sky-blue CP-OLEDs with (R/S)-Czp-tBuCzB showed an external quantum efficiency of 32.1 % with the narrowest full-width at half-maximum of 24 nm among the reported CP-OLEDs, while the devices with (R/S)-Czp-POAB displayed the first nearly pure green CP electroluminescence with |g_EL | factors at the 10^-3 level. These results demonstrate the incorporation of planar chirality into MR-TADF emitter is a reliable strategy for constructing of efficient CP-OLEDs.

Inverted and Amplified CP-EL Behavior Promoted by AIE-Active Chiral Co-Assembled Helical Nanofibers

It is well-known that high-performance circularly polarized organic light-emitting diodes (CP-OLEDs) remain a formidable challenge to the future application of circularly polarized luminescent (CPL)-active materials. Herein, the design of a pair of AIE-active chiral enantiomers (L/D-HP) is described to construct chiral co-assemblies with an achiral naphthalimide dye (NTi). The resulting co-assemblies emit an inverted CPL signal compared with that from the L/D-HP enantiomers. After thermal annealing at 120 °C, the inverted CPL signal of this kind of L/D-HP-NTi with a 1:1 molar ratio shows regular and ordered helical nanofibers arranged through intermolecularly ordered layered packing and is accompanied with a further amplified effect (|g_em | = 0.032, λ_em  = 535 nm). Significantly, non-doped CP-OLEDs based on a device emitting layer (EML) of L/D-HP-NTi exhibits a low turn-on voltage (V_on ) of 4.7 V, a high maximum brightness (L_max ) of 2001 cd m^-2 , and moderate maximum external quantum efficiency (EQE_max ) of 2.3%, as well as excellent circularly polarized electroluminescence (CP-EL) (|g_EL | = 0.023, λ_em  = 533 nm).

Induced CPL-Active Materials Based on Chiral Supramolecular Co-Assemblies

Circularly polarized luminescence (CPL) has attracted much interest due to its potential applications on chiral photonic techniques and optoelectronic materials science. As known, dissymmetry factor (g_em ) of CPL is one essential factor for evaluating the features of CPL-active materials. Much attention has focused on how to increase the g_em value, which is one of the most important issues for CPL practical applications. Recently, more and more works have demonstrated that chiral supramolecular could provide the significant strategy to improve the g_em value through the orderly helical superstructure of chiral building blocks. Normally, this kind of chiral supramolecular assembly process can be accompanied by chirality transfer and induction mechanism, which can promote the amplification effect on the induced CPL of achiral dyes. In this review, we fully summarized recent advances on the induced CPL-active materials of chiral supramolecular co-assemblies, their applications in circularly polarized organic light-emitting diodes (CP-OLEDs) and current challenges.

A three dimensional graphdiyne-like porous triptycene network for gas adsorption and separation

Graphdiyne, an emerging carbon allotrope, has attracted many researchers devoted to the study of its synthesis and application. The utilization of graphdiyne in gas adsorption and separation has been predicted by computer simulation with many examples. In this work, the triangular basic unit of graphdiyne was introduced into a triptycene-based porous organic polymer to obtain a three dimensional graphdiyne-like porous triptycene network named G-PTN. With high surface area and a microporous structure, G-PTN exhibited convincing application potential for the storage of gas molecules, especially for the selective adsorption of acetylene over ethylene. Computational simulation proved the importance of the triptycene units and three dimensional structure to the selectivity, as well as the potential of graphdiyne units as selective binding sites, suggesting that through judicious design, new three-dimensional porous graphdiyne could be acquired with better gas adsorption and separation performance.

Chiral Multi-Resonance TADF Emitters Exhibiting Narrowband Circularly Polarized Electroluminescence with an EQE of 37.2

Highly efficient circularly polarized luminescence (CPL) emitters with narrowband emission remain a formidable challenge for circularly polarized OLEDs (CP-OLEDs). Here, a promising strategy for developing chiral emitters concurrently featuring multi-resonance thermally activated delayed fluorescence (MR-TADF) and circularly polarized electroluminescence (CPEL) is demonstrated by the integration of molecular rigidity, central chirality and MR effect. A pair of chiral green emitters denoted as (R)-BN-MeIAc and (S)-BN-MeIAc is designed. Benefited by the rigid and quasi-planar MR-framework, the enantiomers not only display mirror-image CPL spectra, but also exhibit TADF properties with a high photoluminescence quantum yield of 96 %, a narrow FWHM of 30 nm, and a high horizontal dipole orientation of 90 % in the doped film. Consequently, the enantiomer-based CP-OLEDs achieved excellent external quantum efficiencies of 37.2 % with very low efficiency roll-off, representing the highest device efficiency of all the reported CP-OLEDs.

Circularly Polarized White Organic Light-Emitting Diodes Based on Spiro-Type Thermally Activated Delayed Fluorescence Materials

In this study, we report the first circularly polarized white organic light-emitting diodes (CP-WOLEDs) based on all thermally activated delayed fluorescence (TADF) materials. Two pairs of spiro-type TADF enantiomers, (R/S)-SPOCN (5,5'-((2,2',3,3'-tetrahydro-1,1'-spirobi[indene]-7,7'-diyl)bis(oxy))bis(4-(10H-phenoxazin-10-yl)phthalonitrile)) and (R/S)-OSFSO (2'-(trifluoromethyl)-spiro[quinolino[3,2,1-kl]phenoxazine-9,9'-thioxanthene]-10',10'-dioxide), serve as emitters with complementary emission. The CP-OLEDs exhibit warm white emission with a CIE coordinate of (0.35, 0.46). Besides, decent device performances are observed with an external quantum efficiency of up to 21.6 % at maximum and 11.8 % at 1000 cd m^-2 . Obvious circularly polarized electroluminescence signals are detected with a dissymmetry factor |g_EL | of around 3.0×10^-3 . This is the first report of CP-WOLEDs that can harvest both singlet and triplet excitons, which provides a feasible strategy for the development of CP-WOLEDs with remarkable device performances.

Amplified Circularly Polarized Electroluminescence Behavior Triggered by Helical Nanofibers from Chiral Co-assembly Polymers

Two chiral binaphthyl polymers (R/S-P1 and R/S-P2) with different dihedral angles of the binaphthyl moiety were chosen as chiral inducers to construct chiral co-assemblies with an achiral pyrene-naphthalimide dye (NPy) and then acted as the emitting layer (EML) of circularly polarized electroluminescence (CP-EL) devices. The anchored dihedral angle of R/S-P2 not only exhibited the enhanced chirality signal, but also had a strong chirality-inducing effect on the achiral NPy dye in the chiral co-assembly (R/S-P2)_0.6 -(NPy)_0.4 . After annealing at 120 °C, the CPL signal (|g_em |) of ordered helical nano-fibers (R/S-P2)_0.6 -(NPy)_0.4 was amplified to 5.6×10^-2 , which was about 6-fold larger than that of (R/S-P1)_0.6 -(NPy)_0.4 . The amplified g_em value of (R/S-P2)_0.6 -(NPy)_0.4 was due to the formation of a helical co-assembly through the strong π-π stacking interaction between the R/S-P2 and the achiral NPy. This kind of ordered helical nano-fibers (R/S-P2)_0.6 -(NPy)_0.4 acted as the EML of CP-OLEDs, and achieved an excellent CP-EL performance (|g_EL |=4.8×10^-2 ).

[5]Helicene-based chiral triarylboranes with large luminescence dissymmetry factors over a 10-2 level: synthesis and design strategy via isomeric tuning of steric substitutions

Constructing chiral luminescent systems with both large luminescence dissymmetry factor (g_lum) and high luminous efficiency has been considered a great challenge. We herein describe a highly efficient approach to sterically stabilize the helical configurations of carbo[5]helicenes for improved CPL properties in a series of π-donor and π-acceptor substituted [5]helicenes (1, 2, 3, 4 and 5). Enabled by the ortho-installation of methyl groups as well as the steric effects of triarylamine (Ar₃N) and triarylborane (Ar₃B) handles in meta-substituted [5]helicenes, their optical resolution into enantiomers has been accomplished using preparative chiral HPLC. The molecular chirality of [5]helicenes can be transferred to Ar₃B and Ar₃N as light emitters, which allowed further investigations of their chiroptics, including optical rotation, circular dichroism (CD) and circularly polarized luminescence (CPL). Remarkably, 4 has been demonstrated to display dramatically enhanced CPL performance with a much larger g_lum (>1.2 × 10^-2) and an increased emission quantum efficiency (Φ_S = 0.75) compared with the other analogues, as a result of the isomeric tuning of substitutions with differential steric and electronic effects. These experimentally observed CPL activities were rationalized by TD-DFT computations for the angle (θ_μ,m) between electric and magnetic transition dipole moments in the excited states. In addition, the conspicuous intramolecular donor-acceptor charge transfer led to thermal responses in the emissions of 2 and 4 over a broad temperature range.

High-Performance Circularly Polarized Electroluminescence with Simultaneous Narrowband Emission, High Efficiency, and Large Dissymmetry Factor

Organic light-emitting diodes (OLEDs) that can simultaneously achieve narrowband emission, high efficiency, and circularly polarized luminescence remain a formidable challenge. In this study, a simple strategy is developed to address this challenge. A chiral exciplex-forming co-host is first designed by employing a chiral donor and an achiral acceptor molecule. The chiral exciplex host enables an achiral green multiple-resonance thermally activated delayed fluorescence emitter to achieve high-performance circularly polarized electroluminescence (CP-EL) with a high external quantum efficiency of 33.2%, large electroluminescence dissymmetry factor of 2.8 × 10^-3 , and a small full-width at half-maximum of 42 nm. This work provides a general approach for realizing CP-EL using easily available achiral emitters and can significantly extend the scope of circularly polarized OLEDs.

Chiral Conjugated Thermally Activated Delayed Fluorescent Polymers for Highly Efficient Circularly Polarized Polymer Light-Emitting Diodes

Two novel chiral conjugated polymers R-P and S-P designed and synthesized from a pair of circularly polarized thermally activated delayed fluorescence (CP-TADF) enantiomers are presented in this work. The two polymers exhibited excellent TADF properties with small singlet-triplet energy gaps (ΔE_ST) of 0.045 and 0.061 eV and relatively high photoluminescence quantum yields (PLQYs) of 72 and 76%, respectively. Besides, intense mirror-image circularly polarized luminescence signals were detected from R-P and S-P in both solution and film states with dissymmetry factors (|g_lum|) of up to 1.9 × 10^-3. Furthermore, solution-processed circularly polarized polymer light-emitting diodes (CP-PLEDs) fabricated with R-P and S-P achieved high maximum external quantum efficiencies of 14.9 and 15.8% and high maximum brightness (L_max) of 8940 and 12,180 cd/m² with yellowish-green emission peaks at 546 and 544 nm, respectively. Moreover, intense circularly polarized electroluminescence signals with electroluminescence dissymmetry factors (g_EL) of -1.5 × 10^-3 and +1.6 × 10^-3 were detected from the CP-PLED devices fabricated with R-P and S-P, respectively.

Advances in circularly polarized electroluminescence based on chiral TADF-active materials

This review summarizes the development status of chiral TADF-active materials with CPEL, covering chiral perturbed TADF molecules, intrinsically chiral TADF molecules, and TADFsensitized fluorescent enantiomers.

Introduction of Triptycene with a Particular Substitution Pattern into Polymer Chains Can Dramatically Improve the Structural and Rheological Properties

Although a large number of polymers that contain triptycene units in the main chains have been developed, no polymer design using 1,8-substituted triptycene has been reported to date. In this study, we investigated the properties of linear homo- and copolymers obtained by ring-opening polymerization of a triptycene monomer bearing a macrocyclic olefin linked at its 1,8-position and its copolymerization with cyclooctene, respectively. We found that the introduction of triptycene with this substitution pattern leads to nanoscale molecular ordering, thereby greatly improving the physical properties of the polymers. The key to this remarkable behavior of 1,8-substituted triptycene-containing polymers is the formation of a particular two-dimensional assembly of the triptycene units by nested hexagonal packing, which aligns one-dimensionally while folding the polymer chains into a well-defined layered structure. The polymer design using 1,8-substituted triptycene can be applied to other polymers, unless their main chain contains functional groups capable of a strong intermolecular interaction such as hydrogen bonding.

Two-Dimensional Chiral Polyrotaxane Monolayer with Emergent and Steerable Circularly Polarized Luminescence

Here, we propose a mechanically interlocked strategy to achieve a 2D chiral polyrotaxane (2D CPR) monolayer with emergent and steerable CPL activity by utilizing β-cyclodextrin as the chiral wheel and a luminescent dynamic covalent organic framework as 2D polymeric axle. Such methodology, integrating host-guest and dynamic covalent chemistry, enabled the direct construction of a delaminated 2D CPR monolayer with extraordinarily large size (up to tens of micrometers) and simultaneously endowed chirality to the extended 2D CPR network to generate CPL activity. Importantly, not only the structure but also the CPL performance of the 2D CPR network can be further regulated by the feeding amount of β-cyclodextrin. This work demonstrated a monolayered 2D CPR with CPL activity for the first time. The insightful structure-property relationship of the induced CPL will be of benefit for a deeper understanding of the excited-state chirality of 2D chiral nanomaterials.

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 ΔE_ST accompanied by small k_r , 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 g_lum values, TSCP-type CP-OLEDs with excellent overall performances can be realized.

Red circularly polarized luminescence from intramolecular excimers restricted by chiral aromatic foldamers

Aromatic oligoamide foldamers are highlighted as a verstile paltform for developing single-handed foldamers with two aromatic acetenyl groups at the same side. The foldamers with pyrene acetenyl units exhibit red excimer emissions, which were circularly polarized and show interesting circularly polarized luminescence properties with high CPL brightness B_CPL up to 109.8 M^-1.cm^-1. The red excimer CPL was attributed to the extended conjugations and the spatial restriction of pyrene units at the same side of foldamers.

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.