Highly Efficient Electroluminescence from Narrowband Green Circularly Polarized Multiple Resonance Thermally Activated Delayed Fluorescence Enantiomers

Spiro Units Embedded in the B/N Center for Constructing Highly Efficient Multiple Resonance TADF Emitters

Departing from conventional molecular design strategies that rely on spiro units merely as peripheral components (side chains, terminal groups, or linkage units), we fully or partially incorporate the rigid 9,9'-spirobi[fluorene] (SF) unit into the boron/nitrogen multiple resonances (B/N-MR) emitting core, thereby successfully developing a series of proof-of-concept isomerized multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters, namely SF-BN1, SF-BN2, SF-BN3, and SF-BN4. Remarkably, these novel emitters exhibit exceptionally narrow full-width at half-maximum (FWHM) values of 15-21 nm in dilute toluene solutions and high photoluminescence quantum yields (PLQYs) of up to 90% in doped films. The corresponding organic light-emitting diode (OLED) based on SF-BN1 achieved high external quantum efficiency (EQE) of up to 29.0%, with CIE coordinates of (0.13, 0.08), closely aligning with the BT.2020 blue emission standard. Sky-blue OLEDs based on SF-BN3 can achieve a high EQE of 29.8%, with a narrow FWHM value of 18 nm; the hyperfluorescent (HF) OLEDs based on SF-BN3 improved the EQE of 35.5%. Moreover, we elucidated subtle variations in the connectivity of chemical functional groups within emitters and the polar environment and doping concentrations of OLEDs, which can significantly impact these isomers' optical and electroluminescent (EL) properties.

Highly Efficient Circularly Polarized Luminescence Based on Center-Chiral Frustrated Lewis Pairs

Achieving high-efficiency circularly polarized luminescence (CPL) in organic light-emitting diodes (OLEDs) presents a significant challenge, particularly for center-chiral systems, due to the inherent trade-off between high luminescence efficiency and large luminescence dissymmetry factors. In this work, we introduce a center-chiral frustrated Lewis pair (FLP) design to overcome this limitation. By integrating a stereogenic carbon center into a fluorene scaffold, we create a unique interaction between a boron-based multi-resonance (MR) thermally activated delayed fluorescence (TADF) Lewis acid and an arylamine Lewis base. This sterically hindered design prevents strong charge transfer while optimizing the alignment between electric and magnetic dipole moments for amplified CPL signals. Our OLEDs achieve impressive electroluminescence (EL) dissymmetry factors (|gEL|) of 6.64 × 10-3, external quantum efficiencies (EQEs) of up to 30.4%, and sub-30 nm spectral linewidths. These improvements yield a Figure of Merit (FoM = EQE × |gEL|) of 1.91 × 10-3, the highest reported for center-chiral CPL devices. These findings demonstrate the effectiveness of the center-chiral FLP design in overcoming the long-standing trade-off between polarization and efficiency in CPL devices.

Highly Efficient Narrowband Circularly Polarized Luminescence from Discrete Supramolecular Aggregates

Achieving narrowband emission, high efficiency, and circularly polarized luminescence (CPL) in organic light-emitting diodes (OLEDs) remains a significant challenge. In this study, a discrete supramolecular dimerization strategy is presented to overcome this limitation. By incorporating a helical arylamine with a sterically demanding configuration into a multi-resonance narrowband emitter, the formation of a unique dimeric structure in the solid state is enabled. Unlike conventional multi-resonance emitters prone to aggregation-caused quenching and continuous stacking, the CPL emitters form discrete, well-separated dimers. This distinct supramolecular arrangement not only preserves high photoluminescence quantum yield and narrowband emission but also amplifies CPL signals by optimizing intermolecular electronic coupling. OLEDs incorporating these enantiomers at a 10 wt.% doping level exhibit outstanding performances, including a narrow full-width at half-maximum of 30 nm, maximum external quantum efficiencies (EQE) of 33.5% and 32.4%, and impressive electroluminescence dissymmetry factors (gEL) of +8.7 × 10-3 and -9.1 × 10-3, respectively. Remarkably, increasing the doping concentration to 20 wt.% further boosts the gEL values to +1.6 × 10-2 and -1.8 × 10-2. This enhancement leads to Figures of Merit (EQE × |gEL|) of 3.71 × 10-3 and 4.12 × 10-3, among the highest values for CPL devices.

Comprehensive Review on the Structural Diversity and Versatility of Multi-Resonance Fluorescence Emitters: Advance, Challenges, and Prospects toward OLEDs

Fluorescence emitters with a multiple-resonant (MR) effect have become a research hotspot. These MR emitters mainly consist of polycyclic aromatic hydrocarbons with boron/nitrogen, nitrogen/carbonyl, and indolocarbazole frameworks. The staggered arrangement of the highest occupied molecular orbital and the lowest unoccupied molecular orbital facilitates MR, resulting in smaller internal reorganization energy and a narrower emission bandwidth. Optimal charge separation suppresses the energy gap between singlet and triplet excited states, favoring thermally activated delayed fluorescence (TADF). These MR-TADF materials, due to color purity and high emission efficiency, are excellent candidates for organic light-emitting diodes. Nevertheless, significant challenges remain; in particular, the limitation imposed by the alternated core configuration hinders their diversity and versatility. Most existing MR-TADF materials are concentrated in the blue-green range, with only a few in red and near-infrared spectra. This review provides a timely and comprehensive screening of MR emitters from their pioneering work to the present. Our goal is to gain understandings of the MR-TADF structure-performance relationship from both basic and advanced perspectives. Special emphasis is placed on exploring the correlations between chemical structure, photophysical properties and electroluminescent performance in both depth and breadth with an aim to promote the future development of MR emitters.

Enabling Multicolor Circularly Polarized Organic Long Persistent Luminescence through Chiral Exciplex

Circularly polarized organic long persistent luminescence (CP-OLPL) has garnered significant attention due to its distinctive properties. However, achieving CP-OLPL materials with ultralong durations remains a formidable challenge. Herein, an effective strategy is proposed to obtain long-lived CP-OLPL by constructing a self-designed chiral donor for developing a host-guest chiral exciplex system. The gradual recombination of long-lived charge-separated states enables a green CP-OLPL emission to persist for over 1.5 hours with an asymmetry factor (|glum|) of 4.5 × 10-3. More intriguingly, doping with rubrene fluorophore yields an orange-red CP-OLPL system, exhibiting a duration over 1 hour and |glum| of 2.3 × 10-3 through synergistic singlet-singlet and chirality energy transfer. These properties render the development of chiral afterglow display, multi-level information encryption, and afterglow lighting. This work not only represents a significant advancement in the design of chiral donors for ultralong CP-OLPL exciplex system with durations but also provides valuable insights into exciton dynamics.

Circularly polarized narrowband phosphorescent organic light-emitting diodes

Design strategies for chiral iridium(III) complexes with stable circularly polarized luminescent properties have emerged as important research topics in the field of organic photonics. Given the high rigidity, low chemical activity and multi-closed-loop structure of R-camphor, its chirality cannot be easily affected. Furthermore, the introduction of indolo[3,2,1-jk]carbazole is beneficial for the narrow emission spectrum. Thus, two yellow-emission chiral iridium(III) isomers, Δ-(mpincz)2Ir(R-camphor) and Λ-(mpincz)2Ir(R-camphor), were designed and systematically investigated to elucidate their photophysical properties, chiroptical properties, electrochemical behaviors, theoretical calculations and electroluminescence. The maximum emission peak of racemic Δ/Λ-(mpincz)2Ir(R-camphor) in a degassed toluene solution is located at 560 nm with a full width at half maximum (FWHM) of 48 nm, which demonstrated strong circularly polarized photoluminescence (CPPL) in toluene solution with a luminescent dissymmetry factor (gPL) of 1.15 × 10-3 and -1.0 × 10-3, respectively. Based on Δ-(mpincz)2Ir(R-camphor) and Λ-(mpincz)2Ir(R-camphor), efficient organic light-emitting diodes (OLEDs) were fabricated via vacuum evaporation deposition, with maximum external quantum efficiency (EQEmax) values of 14.65% and 15.58% and asymmetry coefficients (gEL) of 1.86 × 10-4 and -2.29 × 10-4, respectively. This work may provide an effective strategy for the preparation of circularly polarized narrowband Ir(III) complexes.

Peripheral Modification Strategy of Heavy Atom for High-Performance Multi-Resonance Thermally Activated Delayed Fluorescence Emitters

Organic light-emitting materials with multi-resonance thermally activated delayed fluorescence (MR-TADF) have shown great potential for realizing highly efficient narrowband organic light-emitting diodes (OLEDs). However, the heavy efficiency roll-off caused by the slow reverse intersystem crossing (RISC) process remains a challenging issue for the further practical application of MR-TADF materials. Here, we develop two TADF emitters, BNDBT and BNDBF, in which the dibenzothiophene and dibenzofuran substituents are attached at the bottom of the B/N frameworks. They all exhibit the similar high photoluminescence quantum yields of 90 % and 87 %. The sulfur-containing material BNDBT exhibits a RISC rate (kRISC) of 6.02×104 s-1, which is three-folded higher than BNDBF (2.09×104 s-1) without heavy atom. The corresponding green OLED based on BNDBT exhibits an improved external quantum efficiency of 35.5 % and lower efficiency roll-offs at high brightnesses of 100 cd m-2 and 1000 cd m-2, respectively. In addition, the BNDBT-based OLED maintains high color purity without causing a sharp increase in FWHM as compared with that of BNDBF. This work indicates that introducing the heavy atom at the bottom of the B/N skeleton is an effective strategy to enhance kRISC while maintaining narrow FWHM, thereby achieving high-performance MR-TADF emitters.

Circularly polarized electroluminescence from chiral supramolecular semiconductor thin films

Current organic light-emitting diode (OLED) technology uses light-emitting molecules in a molecular host. We report green circularly polarized luminescence (CPL) in a chirally ordered supramolecular assembly, with 24% dissymmetry in a triazatruxene (TAT) system. We found that TAT assembled into helices with a pitch of six molecules, associating angular momentum to the valence and conduction bands and obtaining the observed CPL. Cosublimation of TAT as the "guest" in a structurally mismatched "host" enabled fabrication of thin films in which chiral crystallization was achieved in situ by thermally triggered nanophase segregation of dopant and host while preserving film integrity. The OLEDs showed external quantum efficiencies of up to 16% and electroluminescence dissymmetries ≥10%. Vacuum deposition of chiral superstructures opens new opportunities to explore chiral-driven optical and transport phenomena.

Bifunctional Group Modulation Strategy Enables MR-TADF Electroluminescence Toward BT.2020 Green Light Standard

Herein, a parallel "bifunctional group" modulation method is proposed to achieve controlled modulation of the emission wavelength and full-width at half-maximum (FWHM) values. As a result, three proof-of-concept emitters, namely DBNDS-TPh, DBNDS-DFPh, and DBNDS-CNPh, are designed and synthesized, with the first functional dibenzo[b,d]thiophene unit concurrently reducing the bandgap and elevate their triplet state energy. A second functional group 1,1':3',1″-triphenyl, and electron acceptors 1,3-difluorobenzene and benzonitrile, respectively, to deepen the HOMO and LUMO levels. Accordingly, the CIE coordinates of DBNDS-TPh, DBNDS-DFPh, and DBNDS-CNPh are (0.13, 0.77), (0.14, 0.77), and (0.14, 0.76) respectively, in a dilute toluene solution. This marks the first instance of achieving a CIEy value of 0.77 in dilute toluene solutions. Significantly, the non-sensitized pure-green OLEDs based on DBNDS-TPh and DBNDS-DFPh demonstrate peak EQE of 35.0% and 34.5%, with corresponding CIE coordinates of (0.18, 0.75), (0.17, 0.76) at the doping concentration of 1 wt.%, representing the first green OLED with a CIEy value reaching 0.76 in a bottom-emitting device structure as reported in the literature.

Chiral Blue TADF Materials Enhance the Spin Transitions to Improve Emission Quantum Yield

Circularly polarized thermally activated delayed fluorescence materials not only possess high exciton utilization efficiency but also have the capability to emit circularly polarized light for potential information storage and sensing. In this work, chiral blue TADF enantiomers are prepared. The energy difference between singlet and triplet, ΔEST, increases with the strength of chirality. The chiral orbit-induced spin degeneracy elimination could enhance spin relaxation, where spin could flip easily to lead to an effective transition from triplet to singlet states. This induces a pronounced enhancement in fluorescence quantum yield. Furthermore, circularly polarized emission of chiral TADF materials under different external magnetic fields are studied. Magnetic field control of glum presents a mirror symmetry effect for chiral TADF enantiomers, which provides evidence for the transition between the photon spin and electron spin.

Hyperfluorescence circularly polarized OLEDs consisting of chiral TADF sensitizers and achiral multi-resonance emitters

Developing circularly polarized organic light-emitting diodes (CP-OLEDs) that simultaneously achieve narrow-spectrum emission and high electroluminescence (EL) efficiency remains a formidable challenge. This work prepares two pairs of efficient circularly polarized thermally activated delayed fluorescence (CP-TADF) materials, featuring high photoluminescence quantum yields, short delayed fluorescence lifetimes, good luminescence dissymmetry factors and large horizontal dipole ratios. They can function as emitters for efficient sky-blue CP-OLEDs, providing high maximum external quantum efficiencies (ηext,maxs) (33.8%) and good EL dissymmetry factors (gELs) (-2.64 × 10-3). More importantly, they can work as sensitizers for achiral multi-resonance (MR) TADF emitters, furnishing high-performance blue and green hyperfluorescence (HF) CP-OLEDs with intense narrow-spectrum CP-EL and good ηext,maxs (31.4%). Moreover, tandem HF CP-OLEDs are fabricated for the first time by employing CP-TADF sensitizers and achiral MR-TADF emitters, which radiate narrow-spectrum CP-EL with an extraordinary ηext,maxs (51.3%) and good gELs (4.87 × 10-3). The circularly polarized energy transfer as well as chirality-induced spin selectivity effect of CP-TADF sensitizers are considered to contribute greatly to the generation of efficient CP-EL from achiral MR-TADF emitters. This work not only explores efficient CP-TADF materials but also provides a facile approach to construct HF CP-OLEDs with achiral MR-TADF emitters.

Improving the Blue Color Purity of Tetradentate Pt(II) Complexes with the Assistance of F⋅⋅⋅H Interaction towards High-Performance Blue Phosphorescent OLEDs with EQE over 33

Among the various challenges in the field of organic light-emitting diodes (OLEDs), simultaneously achieving high efficiency, a long lifespan, and a narrow full-width at half maximum (FWHM) in blue OLEDs remains a significant hurdle. Herein, we demonstrate a strategy to improve the color purity of tetradentate Pt(II) complexes with the assistance of ⋅⋅⋅H interaction by incorporating trifluoromethyl (-CF3) groups into the well-known blue tetradentate Pt(II) phosphorescent complex. The results show that the different substitution positions of -CF3 have significantly varying effects on the FWHM values of the complexes; specifically, introducing -CF3 on the benzene ring of carbazole effectively reduces the FWHM, while introducing it on the benzene ring linked to the carbene unit has a minimal impact. When utilized in a mixed host system of SiCzCz/SiTrzCz2, the OLEDs with these new complexes as emitters demonstrated maximum external quantum efficiencies (EQEs) of 27.1 %, 33.8 %, and 27.6 % for PtON-CF3-1, PtON-CF3-2, and PtON-2CF3, respectively, with excellent color purity (CIEy≈0.14 for the PtON-CF3-2 based device). Notably, the device based on PtON-CF3-2 matched the stability of the benchmark PtON-TBBI complex.This work offers an important guideline for the design of high efficient Pt(II) phosphorescent complexes with good blue color purity.

Switchable Topologically Chiral [2]Catenane as Multiple Resonance Thermally Activated Delayed Fluorescence Emitter for Efficient Circularly Polarized Electroluminescence

Aiming at the fabrication of circularly polarized organic light-emitting diodes (CP-OLEDs) with high dissymmetry factors (gEL) and color purity through the employment of novel chiral source, topologically chiral [2]catenanes were first utilized as the key chiral skeleton to construct novel multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters. Impressively, the efficient chirality induction and unique switchable feature of topologically chiral [2]catenane not only lead to a high |gPL| value up to 1.6×10-2 but also facilitate in situ dynamic switching of the full-width at half-maximum (FWHM) and circularly polarized luminescence (CPL). Furthermore, the solution-processed CP-OLEDs based on the resultant topologically chiral emitters exhibit a narrow FWHM of 36 nm, maximum external quantum efficiency of 17.6 %, and CPEL with |gEL| of 2.1×10-3. This study demonstrates the successful construction of the first CP-MR-TADF emitters based on topological chirality with the highest |gPL| among the reported CP-MR-TADF emitters and excellent device performance to the best of our knowledge. Moreover, it endowed the MR-TADF emitter with distinctive switchable CPL performances, thus providing a novel design strategy as well as a promising platform for developing intelligent CP-OLEDs.

Multiple Resonance Quasi-fluorescence from BN-Doped Aromatic Compounds Modified with "Naphthalene" Units Approaches the BT.2020 Green Light Standard

Developing fluorophores that conform to the Broadcast Service Television 2020 (BT.2020) standard presents a formidable challenge. Here, we propose an innovative approach that integrates two and three-boron/nitrogen (BN2)-embedded [4]helicene subunits with naphthalene, resulting in the synthesis of two novel narrowband bright green quasi-fluorescent emitters, NT-2B and NT-3B for ultra-high-definition displays. These emitters exhibit minimal reorganization energy and Huang-Rhys factor, emitting at 510 and 511 nm in dilute toluene solution with exceptionally narrow full width at half maximum values of 15 and 14 nm, respectively. Notably, NT-2B demonstrates an impressive photoluminescence quantum yield of 92.5 %, rapid radiative decay rate, and slow non-radiative decay rate. Owing to their narrowband emission characteristics and outstanding optoelectronic properties, corresponding OLEDs based on NT-2B demonstrate a high external quantum efficiency of 30.6 %, with an FWHM value of 21.5 nm and a CIEy of 0.74, positioning it as one of the leading narrow-band green emitters.

High-Performance Circular Polarization Multiple-Resonance TADF Molecules with Enhanced Long-Range Charge Transfer Based on Chiral Paracyclophane

Circularly polarized multiple-resonance thermally activated delayed fluorescence (CP-MR-TADF) materials have received widespread attention in recent years, but it remains a formidable challenge to design high-performance CP-MR-TADF emitters concurrently exhibiting high quantum efficiency, narrowband emission, and high dissymmetry factor (g). Here, we perform an in-depth theoretical investigation on the CP-MR-TADF materials based on [2.2] paracyclophane (pCp) derivatives. The MR-based materials with enhanced long-range charge transfer (LRCT) characteristics upon excitation show increased g values owing to the coaxial dominated transition components of the transition electric dipole moment (TEDM) and the transition magnetic dipole moment (TMDM) but inevitably result in the loss of narrowband emission performance. Furthermore, the newly designed molecules by fusing the peripheral benzene units of MR cores within the planar chiral pCp bridge maintain narrowband emissions and exhibit increased g values on the order of 1 × 10-3. These findings with rich physical insights on the structure-performance relation of chiral paracyclophane-based molecules should provide important clues for designing high-performance chiral materials.

The Golden Age of Thermally Activated Delayed Fluorescence Materials: Design and Exploitation

Since the seminal report by Adachi and co-workers in 2012, there has been a veritable explosion of interest in the design of thermally activated delayed fluorescence (TADF) compounds, particularly as emitters for organic light-emitting diodes (OLEDs). With rapid advancements and innovation in materials design, the efficiencies of TADF OLEDs for each of the primary color points as well as for white devices now rival those of state-of-the-art phosphorescent emitters. Beyond electroluminescent devices, TADF compounds have also found increasing utility and applications in numerous related fields, from photocatalysis, to sensing, to imaging and beyond. Following from our previous review in 2017 ( Adv. Mater. 2017, 1605444), we here comprehensively document subsequent advances made in TADF materials design and their uses from 2017-2022. Correlations highlighted between structure and properties as well as detailed comparisons and analyses should assist future TADF materials development. The necessarily broadened breadth and scope of this review attests to the bustling activity in this field. We note that the rapidly expanding and accelerating research activity in TADF material development is indicative of a field that has reached adolescence, with an exciting maturity still yet to come.

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.

Nonalternant B,N-Embedded Helical Nanographenes Containing Azepines: Programmable Synthesis, Responsive Chiroptical Properties and Spontaneous Resolution into a Single-Handed Helix

Heteroatom-embedded helical nanographenes (NGs) constitute an important and appealing class of intrinsically chiral materials. In this work, a series of B,N-embedded helical NGs (BN-HNGs) bearing azepines was synthesized via stepwise regioselective cyclodehydrogenation. First, the phenyl- or nitrogen-bridged dimers were efficiently clipped into highly congested model compounds 1 and 2. Later, the controllable Scholl reactions of the tetraphenyl-tethered precursor generated 1, 7 or 8 new C-C bonds, thereby establishing a robust method for the preparation of nonalternant BN-HNGs with up to 31 fused rings. The helical bilayer nature was unambiguously verified by X-ray diffraction analysis. The helical chirality was transferred to the stereogenic boron centers upon fluoride coordination, with a concave-concave structure to comply with the bilayer skeleton. Notably, the largest nonalternant BN-HNG (6) spontaneously resolved into a homochiral 41 helix structure as a molecular spiral staircase during crystallization via conglomerate formation at the single-crystal scale. The large twisted C2-symmetric π-surface and the dynamic chiral skeleton induced by curved azepines might have synergistic effects on self-recognition of enantiomers of 6 to achieve the intriguing spontaneous resolution behavior. The chiroptical properties of the enantiomer of 6 were further investigated, revealing that 6 had a strong chiroptical response in the visible range (400-700 nm).

Helically chiral multiresonant thermally activated delayed fluorescent emitters and their use in hyperfluorescent organic light-emitting diodes

Chiral multiresonant thermally activated delayed fluorescence (MR-TADF) materials show great potential as emitters in circularly polarized (CP) organic light-emitting diodes (CP-OLEDs) owing to their bright and narrowband CP emission. Here, two new chiral MR-TADF emitters tBuPh-BN and DPA-tBuPh-BN possessing intrinsically helical chirality have been synthesized and studied. The large steric interactions between the tert-butylphenyl groups not only induce the helical chirality but also provide a notable configurational stability to the enantiomers. Racemic mixtures of tBuPh-BN and DPA-tBuPh-BN show narrowband emission at 490 and 477 nm with full-width at half maximum (FWHM) of 25 and 28 nm and photoluminescence quantum yields, Φ PL, of 85 and 54% in toluene. The separated enantiomers of tBuPh-BN and DPA-tBuPh-BN show symmetric circularly polarized luminescence (CPL) with respective dissymmetry factors |g PL| values of 1.5 × 10-3 and 0.9 × 10-3. The hyperfluorescence organic light-emitting diodes (HF-OLEDs) with tBuPh-BN and DPA-tBuPh-BN acting as terminal emitters and 2,3,4,5,6-penta-(9H-carbazol-9-yl)benzonitrile (5CzBN) as their assistant dopant exhibited, respectively, maximum external quantum efficiencies (EQEmax) of 20.9 and 15.9% at 492 and 480 nm with FWHM of 34 and 38 nm. This work demonstrates a strategy for developing intrinsically helically chiral MR-TADF emitters possessing significant configurational stability, which can be used in HF-OLEDs.

Regional Functionalization Molecular Design Strategy: A Key to Enhancing the Efficiency of Multi-Resonance OLEDs

Herein, we propose a regional functionalization molecular design strategy that enables independent control of distinct pivotal parameters through different molecule segments. Three novel multiple resonances thermally activated delayed fluorescence (MR-TADF) emitters A-BN, DA-BN, and A-DBN, have been successfully synthesized by integrating highly rigid and three-dimensional adamantane-containing spirofluorene units into the MR framework. These molecules form two distinctive functional parts: part 1 comprises a boron-nitrogen (BN)-MR framework with adjacent benzene and fluorene units forming a central luminescent core characterized by an exceptionally rigid planar geometry, allowing for narrow FWHM values; part 2 includes peripheral mesitylene, benzene, and adamantyl groups, creating a unique three-dimensional "umbrella-like" conformation to mitigate intermolecular interactions and suppress exciton annihilation. The resulting A-BN, DA-BN, and A-DBN exhibit remarkably narrow FWHM values ranging from 18 to 14 nm and near-unity photoluminescence quantum yields. Particularly, OLEDs based on DA-BN and A-DBN demonstrate outstanding efficiencies of 35.0 % and 34.3 %, with FWHM values as low as 22 nm and 25 nm, respectively, effectively accomplishing the integration of high color purity and high device performance.

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

The strategy of integrating conformational isomerization donors and chiral acceptors in a 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 with Commission Internationale de l'Eclairage (CIE) coordinates of (0.30, 0.33) and (0.33, 0.35), respectively. Meanwhile, (R/S)-DO-PTZ exhibited a high PLQY of up to 67 % in doped films and clear mirror-image WCPL signals with a |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 a |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.

Biomimetic Exploration and Reflection on Switchable Coordination and Narrow-Band Electrofluorochromic Devices

Electrofluorochromic (EFC) materials and devices with controllable fluorescence properties show great application potential in advanced anticounterfeiting, information storage and display. However, the low color purity caused by the broad emission spectra and underperforming switching time of the existing EFC materials limit their application. Through biomimetic exploration and the study of reversible electrochemical responsive coordination reactions, boron-nitrogen embedded polyaromatics (B,N-PAHs) with narrow-band emission and high color purity have been successfully integrated into EFC systems, which also help to better understand the role of boron in biological activity. The EFC device achieve good performance containing quenching efficiency greater than 90% within short switching time (ton: 0.6 s, toff: 2.4 s), and nearly no performance change after 200 cycles test. Three primary color (red, green, and blue) EFC devices are successfully prepared. In addition, new phenomena are obtained and discussed in this biomimetic exploration of related boron reactions. The success and harvest of this exploration are expected to provide new ideas for optimizing properties and broadening applications of EFC materials. Moreover, it may provide ideas and reference significance for further exploring and understanding the function of boron compounds in biological systems.

Chiral Co-Assembly with Narrowband Multi-Resonance Characteristics for High-Performance Circularly Polarized Organic Light-Emitting Diodes

A promising kind of ternary chiral co-assemblies with high PLQY, large dissymmetry factor (glum), and narrowband multi-resonance characteristics are achieved by codoped-thermal annealing treatments of achiral luminescent polymer F8BT, chiral inducers R/S-5011, and achiral FRET acceptor DBN-ICZ. The optimized co-assemblies (F8BT)0.9-(R/S-5011)0.1-(DBN-ICZ)0.005 display narrowband yellow emission with full-width half maximum (FWHM) of 37 nm, PLQY of 79%, and intense CPL signals with |glum| of up to 0.26. Meaningfully, solution-processed CP-OLEDs by using those ternary chiral co-assemblies as emitting layer are successfully fabricated, which display yellow circularly polarized electroluminescence (CPEL) with EQEmax of 4.6% and gEL of up to 0.16. The corresponding Q-factor could reach up to 7.36 × 10-3, which is the highest of all the reported CP-OLEDs. Moreover, the devices also exhibit excellent comprehensive device performance with low Von of 7.0 V, high Lmax of about 25 000 cd m-2, extremely low efficiency roll-off with EQE of 4.3% at 10 000 cd m-2, as well as narrowband EL with FWHM of only 39 nm. The proposed ternary co-assembly strategy in fabricating CP-OLED provides the possibility to achieve high comprehensive device performance such as balancing high EQE and large gEL value, as well as narrowband emission, high brightness and low efficiency roll-off simultaneously.

Efficient circularly polarized multiple resonance thermally activated delayed fluorescence from B,N-embedded hetero[8]helicene enantiomers

Helicene-based circularly polarized multiple resonance thermally activated delayed fluorescence (CP-MR-TADF) materials are promising for ultra-high-definition and 3D displays, but most of them encounter potential problems such as easy racemization during the thermal deposition process, low luminous efficiency, and low luminescence dissymmetry factor (g lum), making the development of efficient circularly polarized organic light-emitting diodes (CP-OLEDs) a significant challenge. Here, we report a pair of CP-MR-TADF enantiomers with high-order B,N-embedded hetero[8]helicene, (P/M)-BN-TP-ICz, by fusing two MR chromophores, DtCzB and indolo[3,2,1-jk]carbazole (ICz). BN-TP-ICz exhibits green emission in toluene with a peak of 531 nm and a full-width at half-maximum (FWHM) of 36 nm. The optimized CP-OLEDs with enantiomers (P/M)-BN-TP-ICz exhibit green emission with peaks of 540 nm, FWHMs of 38 nm and Commission Internationale de L'Eclairage coordinates of (0.33, 0.65). Moreover, they showcase maximum external quantum efficiencies (EQEs) of 32.0%, with g ELs of +6.49 × 10-4 and -7.74 × 10-4 for devices based on (P)-BN-TP-ICz- and (M)-BN-TP-ICz, respectively.

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.

Tetraborated Intrinsically Axial Chiral Multi-resonance Thermally Activated Delayed Fluorescence Materials

Chiral multi-resonance thermally activated delayed fluorescence (CP-MR-TADF) materials hold promise for circularly polarized organic light-emitting diodes (CP-OLEDs) and 3D displays. Herein, we present two pairs of tetraborated intrinsically axial CP-MR-TADF materials, R/S-BDBF-BOH and R/S-BDBT-BOH, with conjugation-extended bidibenzo[b,d]furan and bidibenzo[b,d]thiophene as chiral sources, which effectively participate in the distribution of the frontier molecular orbitals. Due to the heavy-atom effect, sulfur atoms are introduced to accelerate the reverse intersystem crossing process and increase the efficiency of molecules. R/S-BDBF-BOH and R/S-BDBT-BOH manifest ultra-pure blue emission with a maximum at 458/459 nm with a full width at half maximum of 27 nm, photoluminescence quantum yields of 90 %/91 %, and dissymmetry factors (|gPL|) of 6.8×10-4/8.5×10-4, respectively. Correspondingly, the CP-OLEDs exhibit good performances with an external quantum efficiency of 30.1 % and |gEL| factors of 1.2×10-3.

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.

Two Different Chiral Groups Based Thermally Activated Delayed Fluorescence Materials for Circularly Polarized OLEDs

Circularly polarized organic light-emitting diodes (CP-OLEDs) hold significant promise for applications in 3D displays due to the ability to generate circularly polarized luminescence (CPL) directly. In this study, two pairs of circularly polarized thermally activated delayed fluorescence (CP-TADF) enantiomers, named RR/SS-ONCN and RS/SR-ONCN, were synthesized by integrating two distinct chiral groups into the dicyanobenzene unit. The RR/SS-ONCN and RS/SR-ONCN enantiomers show CPL properties with dissymmetry photoluminescence factors (|gPL|) of 1.3×10-3 and 2.0×10-3 in doped films, respectively. Notably, RR/SS-ONCN exhibit higher |gPL| values than that of RS/SR-ONCN, especially in doped films, indicating that when the configurations of the two chiral groups are identical, the |gPL| value of the CP-TADF materials can be enhanced, demonstrating a certain stacking effect. Moreover, the corresponding CP-OLEDs demonstrate good performances, achieving maximum external quantum efficiencies of up to 21.9 % and notable CP electroluminescence with |gEL| factors of up to 1.0×10-3.

Flexible Full-Inorganic Ultrathin Films with Stable Circularly Polarized Luminescence Covering the Visible to Near-Infrared Region

Circularly polarized luminescence (CPL) materials hold significant value in various fields, including information storage, secure communication, three-dimensional displays, biological detection, and optoelectronic devices. Using the Langmuir-Schaeffer (LS) assembly technique, we successfully construct a series of large-area flexible optical ultrathin films. Impressively, the inorganic assembled ultrathin films exhibit excellent CPL optical activity covering the visible to near-infrared (NIR) region, with the luminescence asymmetry factor glum ranging from 0.59 to 0.72. Moreover, such ultrathin films also display outstanding mechanical flexibility, the optical activity of which even after 240 bending cycles shows almost no difference compared to the unbent samples. Owing to the ultra-broadband optical activity and ultra-stable optical activity of such full-inorganic assembled materials on flexible substrates, coupled with their excellent processability and outstanding mechanical flexibility, we anticipate they will find use in many fields such as communication technology and flexible optoelectronics.

Stepwise Charge/Energy Transfer in MR-TADF Molecule-Doped Exciplex for Ultralong Persistent Luminescence Activated with Visible Light

Organic long-persistent luminescence (OLPL), which relies on energy storage for delayed light emission by the charge separation state, has attracted intense attention in various optical applications. However, charge separation (CS) is efficient only under ultraviolet excitation in most OLPL systems because it requires a driving force from the large energy difference between the local excited (LE) and charge transfer (CT) states. In this study, a multiresonance thermally activated delayed fluorescence (MR-TADF) molecule is incorporated into an exciplex system to achieve efficient OLPL in a composite material activated by visible light via a stepwise charge/energy transfer process. The enhanced absorption of the composite material facilitated a tenfold increase in the duration of the OLPL, which can last for several hours under visible light excitation. The excited state of the MR-TADF molecule tends to charge transfer to the acceptor, followed by energy transfer to the exciplex, which benefits from the small difference between the LE and CT states owing to the inherent CS characteristics of the opposing resonance effect. Afterglow displays of these composite materials are fabricated to demonstrate their considerable potential in encryption patterns and emergency lights, which take advantage of their excellent processability, visible light activation, and tunable luminescence properties.

A diphenylphosphine oxide decorated multi-resonance TADF emitter for narrowband green electroluminescence with an EQE of 32.4

A new narrowband thermally activated delayed fluorescence emitter, PhCzBN-PO, was developed by incorporating the diphenylphosphine oxide (DPPO) group into a multi-resonance core. The unique properties of DPPO enabled PhCzBN-PO to achieve pure green emission and a nonplanar structure. The resulting electroluminescent devices achieved high external quantum efficiencies up to 32.4% with extremely low efficiency roll-off and pure-green emission with Commission Internationale de L'Eclairage (CIE) coordinates of (0.24, 0.67).

An electrochemically responsive B-O dynamic bond to switch photoluminescence of boron-nitrogen-doped polyaromatics

Boron-doped polycyclic aromatic hydrocarbons exhibit excellent optical properties, and regulating their photophysical processes is a powerful strategy to understand the luminescence mechanism and develop new materials and applications. Herein, an electrochemically responsive B-O dynamic coordination bond is proposed, and used to regulate the photophysical processes of boron-nitrogen-doped polyaromatic hydrocarbons. The formation of the B-O coordination bond under a suitable voltage is confirmed by experiments and theoretical calculations, and B-O coordination bond can be broken back to the initial state under opposite voltage. The whole process is accompanied by reversible changes in photophysical properties. Further, electrofluorochromic devices are successfully prepared based on the above electrochemically responsive coordination bond. The success and harvest of this exploration are beneficial to understand the luminescence mechanism of boron-nitrogen-doped polyaromatic hydrocarbons, and provide ideas for design of dynamic covalent bonds and broaden material types and applications.

Promising interlayer sensitization strategy for the construction of high-performance blue hyperfluorescence OLEDs

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials are promising candidates for organic light-emitting diodes (OLEDs) with narrow electroluminescence (EL) spectra. Current researches focus on fabricating hyperfluorescence OLEDs to improve EL efficiencies of MR-TADF emitters by co-doping them with TADF sensitizers in a single host layer. However, in many cases, the polarity of the single host could be not suitable for both blue MR-TADF emitters and blue TADF sensitizers, resulting in broadened EL spectra in high-polar hosts or decreased EL efficiencies in low-polar hosts. Herein, we wish to report an efficient sensitization strategy for blue MR-TADF emitters by constructing an interlayer-sensitizing configuration, in which the blue TADF sensitizers and blue MR-TADF emitters are separated into two closely aligned host layers with high polarity and low polarity, respectively. Based on this strategy, efficient blue hyperfluorescence OLEDs are realized and verified by employing various TADF sensitizers and different MR-TADF emitters, furnishing outstanding external quantum efficiencies of up to 38.8% and narrow EL spectra. These results validate the feasibility and universality of this interlayer sensitization strategy, which provides an effective alternative to high-performance blue hyperfluorescence OLEDs.

Synthetic progress of organic thermally activated delayed fluorescence emitters via C-H activation and functionalization

Thermally activated delayed fluorescence (TADF) emitters have become increasingly prominent due to their promising applications across various fields, prompting a continuous demand for developing reliable synthetic methods to access them. This review aims to highlight the progress made in the last decade in synthesizing organic TADF compounds through C-H bond activation and functionalization. The review begins with a brief introduction to the basic features and design principles of TADF emitters. It then provides an overview of the advantages and concise development of C-H bond transformations in constructing TADF emitters. Subsequently, it summarizes both transition-metal-catalyzed and non-transition-metal-promoted C-H bond transformations used for the synthesis of TADF emitters. Finally, the review gives an outlook on further challenges and potential directions in this field.

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.

Tetraphenylethene-modified polysiloxanes: Synthesis, AIE properties and multi-stimuli responsive fluorescence

Herein, polysiloxane-based aggregation-induced emission (AIE) polymers and rubbers were prepared which display interesting multi-stimuli responsive fluorescence. TPE-modified polydimethylsiloxanes (PDMS-TPE) as polysiloxane-based AIE polymers were synthesized through Heck reaction of bromo-substituted tetraphenylethene (TPE-Br) and vinyl polysiloxanes. As expected, TPE moiety endows the modified polysiloxane with typical AIE behavior. However, limited by the long polymer chains, the aggregation process of PDMS-TPE shows obvious differences compared with the small molecule TPE-Br. The fluorescence of PDMS-TPE in THF/H2O starts to increase when the H2O fraction (fw) is 70% while TPE-Br is nearly non-luminous until the fw is up to 99%. The fluorescence intensity ratio (I/I0) of PDMS-TPE in the aggregated state and dispersed state is over 1300, greater than that of TPE-Br (I/I0 = 380). More importantly, the exceptional thermal motion of Si-O-Si chains and AIE characteristic of TPE moiety work together, enabling PDMS-TPE to show specific temperature-dependent fluorescence with a wider response range of room temperature to 190°C, which is distinguished from TPE-Br. And such fluorescence responsiveness possess good fatigue-resistance. Furthermore, fluorescent silicone rubbers, r-PDMS-TPE were prepared by using PDMS-TPE as additive of the base gum. They display interesting solvent-controllable fluorescence and higher tensile strength (4.42 MPa) than the control sample without TPE component (1.96 MPa). Notably, a unique stretching-enhanced emission (SEE) phenomenon is observed from these TPE-modified silicone rubbers. When being stretched, the rubbers' fluorescent emission intensity could increase by 143%.

Recent Advances of Chiral Isolated and Small Organic Molecules: Structure and Properties for Circularly Polarized Luminescence

This paper explores recent advancements in the field of circularly polarized luminescence (CPL) exhibited by small and isolated organic molecules. The development and application of small CPL molecule are systematically reviewed through eight different chiral skeleton sections. Investigating the intricate interplay between molecular structure and CPL properties, the paper aims at providing and enlighting novel strategies for CPL-based applications.

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.

Bridging of Cove Regions: A Strategy for Realizing Persistently Chiral Double Heterohelicenes with Attractive Luminescent Properties

The racemization of chiral organic compounds is a common chemical phenomenon. However, it often poses configurational-stability issues to the application of this class of compounds. Achieving chiral organic compounds without the risk of racemization is fascinating, but it is challenging due to a lack of strategies. Here, we reveal the cove-regions bridging strategy for achieving persistently chiral multi-helicenes (incapable of racemization), based on the synthesized proof-of-concept double hetero[4]helicenes featuring macrocycle structures with a small 3D cavity. Additionally, we demonstrate that the strategy is also effective in tuning the electronic structures of multi-helicenes, resulting in a conversion from luminescence silence into thermally activated delayed fluorescence (TADF) for the present system. Furthermore, red circularly polarized TADF based on small double [4]helicene systems is achieved for the first time using this strategy. The disclosed cove-regions bridging strategy provides an opportunity to modulate the electronic structures and luminescent properties of multi-helicenes without concern for racemization, thus significantly enhancing the structural and property diversity of multi-helicenes for various applications.

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.

Diradical-Based Strategy in Designing Narrowband Thermally Activated Delayed Fluorescence Molecules with Tunable Emission Wavelengths

In the design of thermally activated delayed fluorescence (TADF) materials, narrow-band emission is of particular importance for the development of organic light-emitting diodes (OLEDs). In this work, we proposed a new strategy for designing TADF molecules utilizing degenerate nonbonding (NB) orbitals of diradical parent molecules, and these designed molecules are termed NB-TADF molecules. Based on this strategy, a series of NB-TADF molecules is finely designed and systematically studied by theoretical calculations. Taking advantage of the nonbonding properties, these NB-TADF molecules exhibit desirable narrowband emissions and high quantum yields. More importantly, the emission bands can be easily tuned from blue to near-infrared by changing the conjugate length of the parent group in the NB-TADF molecules. We hope that this new strategy can open a new door for the design of novel TADF materials.

Functionalization of the Octahydro-Binaphthol Skeleton: A Universal Strategy for Directly Constructing D-A Type Axially Chiral Biphenyl Luminescent Molecules

D-A type axially chiral biphenyl luminescent molecules are directly constructed through ingenious functionalization of the octahydro-binaphthol skeleton without optical resolution. The circularly polarized organic light-emitting diodes based on them display remarkable circularly polarized electroluminescence emission, a high luminance of >10 000 cd m-2, a maximum external quantum efficiency of 6.6%, and an extremely low-efficiency roll-off. This work provides a universal strategy for developing efficient and diverse axially chiral biphenyl emitters.

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.

High-Efficiency and Narrowband Green Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes Based on Two Diverse Boron Multi-Resonant Skeletons

Up to now, highly efficient narrowband thermally activated delayed fluorescence (TADF) molecules constructed by oxygen-bridged boron with an enhancing multiple resonance (MR) effect have been in urgent demand for solid-state lighting and full-color displays. In this work, a novel MR-TADF molecule, BNBO, constructed by the oxygen-bridged boron unit and boron-nitrogen core skeleton as an electron-donating moiety, is successfully designed and synthesized via a facile one-step synthesis. Based on BNBO as an efficient green emitter, the organic light-emitting diode (OLED) shows a sharp emission peak of 508 nm with a full-width at half-maximum (FWHM) of 36 nm and realizes quite high peak efficiency values, including an external quantum efficiency (EQEmax) of 24.3% and a power efficiency (PEmax) of 62.3 lm/W. BNBO possesses the intramolecular charge transfer (ICT) property of donor-acceptor (D-A) materials and multiple resonance characteristics, which provide a simple strategy for narrowband oxygen-boron materials.

Organoboron-based multiple-resonance emitters: synthesis, structure-property correlations, and prospects

Boron-based multiple-resonance (MR) emitters exhibit the advantages of narrowband emission, high absolute photoluminescence quantum yield, thermally activated delayed fluorescence (TADF), and sufficient stability during the operation of organic light-emitting diodes (OLEDs). Thus, such MR emitters have been widely applied as blue emitters in triplet-triplet-annihilation-driven fluorescent devices used in smartphones and televisions. Moreover, they hold great promise as TADF or terminal emitters in TADF-assisted fluorescence or phosphor-sensitised fluorescent OLEDs. Herein we comprehensively review organoboron-based MR emitters based on their synthetic strategies, clarify structure-photophysical property correlations, and provide design guidelines and future development prospects.

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.

Frontier Molecular Orbital Engineering of Aromatic Donor Fusion: Modularly Constructing Highly Efficient Narrowband Yellow Electroluminescence

The development of high-performance multiple resonance thermally activated delayed fluorescence (MR-TADF) materials with narrowband yellow emission is highly critical for various applications in industries, such as the automotive, aerospace, and microelectronic industries. However, the modular construction approaches to expeditiously access narrowband yellow-emitting materials is relatively rare. Here, a unique molecular design concept based on frontier molecular orbital engineering (FMOE) of aromatic donor fusion is proposed to strategically address this issue. Donor fusion is a modular approach with a "leveraging effect"; through direct polycyclization of donor attached to the MR parent core, it is facile to achieve red-shifted emission by a large margin. As a result, two representative model molecules, namely BN-Cz and BN-Cb, have been constructed successfully. The BN-Cz- and BN-Cb-based sensitized organic light-emitting diodes (OLEDs) exhibit bright yellow emission with peaks of 560 and 556 nm, full-width at half-maxima (fwhm's) of 49 and 45 nm, Commission Internationale de L'Eclairage coordinates of (0.44, 0.55) and (0.43, 0.56), and maximum external quantum efficiencies (EQEs) of 32.9% and 29.7%, respectively. The excellent optoelectronic performances render BN-Cz and BN-Cb one of the most outstanding yellow-emitting MR-TADF materials.

Introduction of a Chiral Biphenanthrene-Diol Unit to Achieve Circularly Polarized Thermally Activated Delayed Fluorescence

Circularly polarized luminescence (CPL) materials are promising candidates for future display technology. However, such highly efficient emitters suffer from the issues of difficult chiral separation and low photoluminescence quantum yield (PLQY). In this work, the chiral 4,4'-biphenanthrene-3,3'-diol (BIPOL) unit was introduced into a thermally activated delayed fluorescence (TADF) framework for the first time. We presented two series of enantiomers, R/S-o-DCzBPNCN and R/S-p-DCzBPNCN, and the synthesis of enantiopure BIPOL can be prepared via normal column chromatography. Notably, o-DCzBPNCN showed narrow singlet-triplet gap of 0.05 eV, efficient TADF, and high PLQYs of 82 % in doped films. In addition, R/S-o-DCzBPNCN exhibited high luminescence dissymmetry factor (gPL ) values of -1.94×10-2 /+1.91×10-2 in doped films. The strategy of BIPOL introduction offers a new approach to organic emitters with stereospecific synthesis, TADF, and chiroptical properties.

Deep-Blue Narrowband Hetero[6]helicenes Showing Circularly Polarized Thermally Activated Delayed Fluorescence Toward High-Performance OLEDs

Helicenes exhibit substantial potential as circularly polarized luminescence (CPL) active molecules. However, their application in circularly polarized organic light-emitting diodes (CP-OLEDs) is typically hindered by the challenge of integrating both high color purity and efficient triplet-harvesting capability, particularly in the blue spectral region. Herein, a series of hetero[6]helicene-based emitters that is strategically engineered through the helical extension of a deep-blue double-boron-based multiple resonance thermally activated delayed fluorescence (MR-TADF) motif, is introduced. Importantly, the helical extension does not cause apparent structural deformation or perturb frontier molecular orbitals; thus, preserving the deep-blue emission and MR-TADF characteristics of the parent molecule. This approach also leads to reduced reorganization energy, resulting in emitters with narrower linewidth and higher photoluminescence quantum yield. Further, the helical motif enhances the racemization barrier and leads to improved CPL performance with luminescence dissymmetry factor values up to 1.5 × 10-3 . Exploiting these merits, devices incorporating the chiral dopants demonstrate deep-blue emission within the Broadcast Service Television 2020 color-gamut range, record external quantum efficiencies (EQEs) up to 29.3%, and have distinctive circularly polarized electroluminescence (CPEL) signals. Overall, the authors' findings underscore the helical extension as a promising strategy for designing narrowband chiroptical materials and advancing high-definition displays.

Indolo[3,2-b]indole-based multi-resonance emitters for efficient narrowband pure-green organic light-emitting diodes

Organic light-emitting diodes (OLEDs) utilizing multi-resonance (MR) emitters show great potential in ultrahigh-definition display benefitting from superior merits of MR emitters such as high color purity and photoluminescence quantum yields. However, the scarcity of narrowband pure-green MR emitters with novel backbones and facile synthesis has limited their further development. Herein, two novel pure-green MR emitters (IDIDBN and tBuIDIDBN) are demonstrated via replacing the carbazole subunits in the bluish-green BCzBN skeleton with new polycyclic aromatic hydrocarbon (PAH) units, 5-phenyl-5,10-dihydroindolo[3,2-b]indole (IDID) and 5-(4-(tert-butyl)phenyl)-5,10-dihydroindolo[3,2-b]indole (tBuIDID), to simultaneously enlarge the π-conjugation and enhance the electron-donating strength. Consequently, a successful red shift from aquamarine to pure-green is realized for IDIDBN and tBuIDIDBN with photoluminescence maxima peaking at 529 and 532 nm, along with Commission Internationale de l'Eclairage (CIE) coordinates of (0.25, 0.71) and (0.28, 0.70). Furthermore, both emitters revealed narrowband emission with small full width at half-maximum (FWHM) below 28 nm. Notably, the narrowband pure-green emission was effectively preserved in corresponding devices, which afford elevated maximum external quantum efficiencies of 16.3% and 18.3% for IDIDBN and tBuIDIDBN.