Rong-Huei Yi

Multiple donors have been integrated into multi-resonance moieties to engineer excited states and steric hindrances to generate blue and green thermally activated delayed fluorescence molecules with enhanced quenching resistance and spin-flip processes. The resulting organic light-emitting diodes show high external quantum efficiencies, reduced efficiency roll-offs, and good operational stability across a wide dopant concentration.

Abstract

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials have great potential for applications in ultrahigh-definition (UHD) organic light-emitting diode (OLED) displays, that benefit from their narrowband emission characteristic. However, key challenges such as aggregation-caused quenching (ACQ) effect and slow triplet-to-singlet spin-flip process, especially for blue MR-TADF materials, continue to impede their development due to planar skeletons and relatively large ΔE _STs. Here, an effective strategy that incorporates multiple carbazole donors into the parent MR moieties is proposed, synergistically engineering their excited states and steric hindrances to enhance both the spin-flip process and quenching resistance. As expected, the designed materials namely 5Cz-BNO and 5Cz-BN exhibit bright blue and green emissions with narrow full-width at half-maximums (FWHMs) around 23 nm, together with significantly improved reverse intersystem crossing (RISC) rates. The OLEDs based on 5Cz-BNO and 5Cz-BN with doping concentrations from 5 to 20 wt % achieve high maximum external quantum efficiency (EQE_max) values exceeding 30 % with suppressed efficiency roll-offs and improved operational stability. This work offers an effective approach for designing doping-insensitive blue and green MR-TADF materials with fast spin-flip processes by integrating the engineering of excited states and steric hindrances.

A series of π-extended helical nanographenes have been explored for their optical and chiroptical properties. The introduction of an additional helical subunit with preferred handedness controls and boosts the optical and chiroptical properties including dissymmetry factor (g_lum), fluorescence quantum yield (φ), and circularly polarized luminescence brightness (B_CPL) of the helical nanographene.

Abstract

Nanographenes have captivated scientific interest since the pioneering discovery of graphene. Recently, attention has shifted towards exploring chiral and nonplanar nanographenes, for their distinct optical, chiroptical, and electronic properties. Despite the growing acceptance of helicenes, the research on inducing helical chirality on π-extended derivatives to boost chiroptical properties remains unattended. In our study, we introduce a new π-extended [7]-helicene resulting from the condensation of diamines with 3,6-dibromophenanthrene-9,10-dione, complemented by two hexabenzocoronene arms in the periphery. Notably, the nanographene containing binaphtho-[1,4]diazocine, compared to the corresponding phenazine, exhibits a remarkable average 2.5, 5, and 10-fold enhancements in quantum yield, dissymmetry factor, and brightness, respectively, when measured in five different solvents. These improvements underscore the significance of the induced helical chirality by the antiaromatic binaphtho-[1,4]diazocine in influencing the chiroptical properties of the helical nanographene. Our research represents a significant stride toward unlocking the potential of π-extended helicenes and lays the groundwork for further exploration in designing and synthesizing new chiral nanomaterials.

Intramolecular anagostic Cu⋅⋅⋅H interactions are leveraged for the design of luminescent low-coordinate copper(I) complexes. Without using sterically bulky substituents on the carbene ligand, the copper(I) complexes exhibit excellent thermal stability. Featuring with high-efficiency and short-lived thermally activated delayed fluorescence, the copper(I) complexes demonstrate exceptional electroluminescence properties with high external quantum efficiency, little efficiency roll-off and long operational lifetimes.

Abstract

Although two-coordinate Cu(I) complexes are highly promising low-cost emitters for organic light-emitting diodes (OLEDs), the exposed metal center in the linear coordination geometry makes them suffer from poor stability. Herein, we describe a strategy to develop stable carbene-Cu-amide complexes through installing intramolecular noncovalent Cu⋅⋅⋅H interactions. The employment of 13H-dibenzo[a,i]carbazole (DBC) as the amide ligand leads to short Cu⋅⋅⋅H distances in addition to the Cu−N coordination bond. The resultant Cu(I) complexes exhibit yellow thermally activated delayed fluorescence with photoluminescence quantum yields of up to 86 % and radiative decay rate constants on the order of 10⁶ s⁻¹. Comparing with the analogues without Cu⋅⋅⋅H interactions, the pincer complexes have significantly improved stability. The vacuum-deposited OLEDs show high-performance electroluminescence with maximum external quantum efficiencies of up to 29.5 % and extremely small roll-offs of only 3.5 % at 10,000 cd m⁻². Remarkably, the operational lifetimes (LT₉₀) are up to 68 h with an initial luminance of 3000 cd m⁻². This work proves a feasible design of robust low-coordinate metal complexes by leveraging secondary coordination interactions, which helps to overcome the long-standing stability problem.

The incorporation of two boron atoms within a tetraazacyclophane architecture by a multiple resonance thermally activated delayed fluorescence design has led to a highly efficient ultra-narrowband yellow emitter, HBN, with a maximum at 572 nm and an impressively narrow full-width at half-maximum of 17 nm. Incorporation of HBN into an organic light-emitting diode led a high maximum external quantum efficiency of 36.1 %.

Abstract

Ultra-narrowband and highly modifiable multiple resonance thermally activated delayed fluorescence (MR-TADF) materials are crucial for realizing high-performance wide-color-gamut display applications. Despite progress, most MR-TADF emitters remain confined to blue and green wavelengths, with difficulties extending into longer wavelengths without significant spectral broadening, which compromises color purity in full-color organic light-emitting diode (OLED) displays. In this work, we present a novel tetraazacyclophane-based architecture embedding dual boron atoms to remarkedly enhance intramolecular charge transfer through the strategic positioning of boron and nitrogen atoms. This arrangement induces a substantial redshift while maintaining structural rigidity and molecular orbital symmetry, with a hole-electron central distance of 0 Å, allowing for ultra-narrowband emission. The resulting MR-TADF material, HBN, delivers yellow emission peaking at 572 nm (2.168 eV) with an impressively narrow full-width at half-maximum (FWHM) of 17 nm (0.064 eV) in dilute toluene. Moreover, the corresponding phosphorescent-sensitized fluorescence OLED achieves yellow emission maximum at 581 nm, with a narrow FWHM of 25 nm, a high maximum external quantum efficiency of 36.1 %, and a luminance exceeding 40,000 cd m⁻². These outstanding photoluminescent and electroluminescent performances validate the superiority of our molecular design strategy, highlighting its significant potential for cutting-edge optoelectronic applications.

The TADF luminescent Cu(I) metallacycle B carrying unusual semi-bridging aqua ligands has been prepared in a one-step high-yield reaction. When B is heated markedly above room temperature, a solid-state reaction affords a new metallacycle C displaying TADF luminescence different from that of B. The removal of the aqua ligands and the formation of cuprophilic interactions makes this transition an innovative example of a solid-state photoactive tracer.

Abstract

A new luminescent Cu(I) tetrametallic metallacycle B is reported that features very rare semi-bridging aqua ligands. When heated markedly above room temperature, this compound undergoes a post-synthetic transformation in the solid-state, affording the new luminescent metallacycle C. Thermogravimetric analysis, IR spectroscopy and single-crystal X-ray diffraction reveal that this alteration preserves the gross tetrametallic macrocycle structure, but is caused by the release of the coordinated water molecules with the concomitant formation of cuprophilic interactions. This transition induces a shift from eye-perceived green (B) to blue (C) room-temperature luminescence for these molecular solids. Photophysical measurements and time-dependent density-functional theory calculations have been conducted to identify the origins of the emission properties lying in these structurally related assemblies, and suggest that thermally activated delayed fluorescence dominates the radiative relaxation pathways. This study highlights the innovative feature of Cu(I) derivatives, offering access to stimuli-sensitive materials that can witness, a posteriori, the exceeding of critical temperatures in their environment.

By utilizing isomeric molecular engineering to tune electronic and vibrational spin-orbital coupling effects, several chiral molecules have been developed to exploit both thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) mechanisms for efficient luminescence. The TADF-based OLEDs achieve a high external quantum efficiency of 30.1 %, and by modulating the TADF and RTP emissions, single-molecule white emission has been realized.

Abstract

The exploration of circularly polarized luminescence is important for advancing display and lighting technologies. Herein, by utilizing isomeric molecular engineering, a novel series of chiral molecules are designed to exploit both thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) mechanisms for efficient luminescence. The cooperation of a small singlet-triplet energy gap, moderate spin-orbital coupling (SOC), and large oscillator strength enables efficient TADF emission, with photoluminescence quantum yields exceeding 90 %. By altering the symmetry of molecular structures, it is demonstrated that the intrinsic electronic SOC and vibrational SOC effects can be greatly enhanced to facilitate RTP emission. Notably, through modulating simultaneous TADF and RTP emissions, single-molecule white emission is successfully achieved. Accordingly, the TADF-based organic light-emitting diode (OLED) achieves a maximum external quantum efficiency up to 30 %, representing exceptional performance of non-aromatic amine-based emitters. Furthermore, the first single-molecule white OLED based on TADF and RTP dual-emissive chiral material is developed, establishing a benchmark for the development of advanced display and lighting technologies.

Synergistic modulation of π-conjugation and electron-donating strengths has been used to induce hybridized localized electronic and charge-transfer characters. This has led to donor-acceptor-donor (π-DAD) structures showing a maintained elevated two-photon absorption cross-section value and highly efficient thermally activated delayed fluorescence.

Abstract

The pursuit of highly efficient thermally activated delayed fluorescence (TADF) emitters with two-photon absorption (2PA) character is hampered by the concurrent achievement of a small singlet-triplet energy gap (ΔE _ST) and high photoluminescence quantum yield (Φ _PL). Here, by introducing a terephthalonitrile unit into a sterically crowded donor-π-donor structure, inducing a hybrid electronic excitation character, we designed unique TADF emitters possessing 2PA ability. This rational molecular design was achieved through a main π-conjugated donor-acceptor-donor backbone in line with locally excited feature renders a large oscillator strength and transition dipole moment, maintaining a high 2PA cross-section value. The ancillary N-donor-acceptor-donor with charge transfer character highly balances the TADF phenomenon by minimizing ΔE _ST. A near-unity Φ _PL value with a large radiative decay rate over an order of magnitude higher than the intersystem crossing rate and a high horizontal orientation ratio of 0.95 were simultaneously attained for TPCz2NP. The organic light-emitting diodes fabricated with this material exhibit a high maximum external quantum efficiency of 25.4 % with an elevated 2PA cross-section (σ₂ ) value up to 143 GM at 850 nm. These findings offer a venue for designing high-performance TADF emitters with exceptional performance inclusive of 2PA properties, expanding for future functional material design.

Achieving high efficiency narrowband near-ultraviolet (NUV) emitters in organic light emitting diode (OLED) is still a formidable challenge. Herein, a proof-of-concept hybridized local and charge transfer (HLCT) molecule, named ICz-BO, is prepared and characterized, in which both multiresonant (MR) skeletons are integrated via conjugation connection. A slightly distorted structure and weak intramolecular charge transfer (CT) interaction between two MR subunits lead to a high-lying reverse intersystem crossing (h-RISC) channel of T6→S1, also evidenced by both experimental and calculated results. Impressively, the ICz-BO emitter exhibits outstanding narrowband NUV emission at 404 nm with a full-width at half maximum of 28 nm in toluene solution. The solution processable OLED shows an excellent device performance with the recorded maximum external quantum efficiency of 12.01%, concomitant with an extremely low y-axis Commission Internationale de l’Éclairage (CIEy) value of 0.031. To the best of our knowledge, this is the highest efficiency reported for the HLCT-based NUV-OLEDs to date. This research proves that the MR skeleton plays a positive effect on the narrowband hot exciton emitter, which provides an alternative paradigm for developing high-efficiency NUV emitters.

A series of chiral thermally activated delayed fluorescence polymers (R/S)-E-x (x = 0.02, 0.05, and 0.1) are designed and prepared. Impressively, solution-processable single-emitting-layer circularly polarized white organic light-emitting diode is achieved by employing the chiral polymers and 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) via electroplex emission strategy, which shows the best performances with a maximum external quantum efficiency of 15.1% and charming electroluminescence dissymmetry factor of 2.4 × 10⁻³.

Abstract

Achieving efficient circularly polarized white organic light-emitting diode (CP-WOLED) remains a significant challenge. In this study, a proof-of-concept for realizing CP-WOLED is proposed using an electroplex emission strategy between a chiral thermally activated delayed fluorescence (TADF) emitter and hole-transporting material. A series of chiral polymers (R/S)-E-x (x = 0.02, 0.05, and 0.1) are designed and prepared via random copolymerization of a chiral chromophore and styrene moiety, which shows typical TADF character. The neat film of (R/S)-E-0.1 presents distinct chiroptical properties with a dissymmetry factor (|g _lum|) of 2.8 × 10⁻³. Notably, solution-processable, single-emitting-layer CP-WOLEDs are fabricated using these chiral polymers in combination with 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) as the emitter, achieving a record maximum external quantum efficiency of 15.1% and Commission Internationale de lʹeclairage coordinate of (0.36, 0.40). Importantly, these CP-WOLEDs exhibit an impressive |g _EL| value of 2.4 × 10⁻³. This research provides a straightforward and effective strategy for the realization of high-performance CP-WOLED.

Through-space charge transfer (TSCT) materials show potential for optoelectronic applications. This study unravels how spatial configuration impacts TSCT properties. Different photophysical properties were observed in a series of spiro-based TSCT materials. Their external quantum efficiencies range from 28.0 % to 3.6 %, highlighting the importance of spatial arrangement.

Abstract

Thermally activated delayed fluorescence (TADF) materials hold promise for optoelectronic applications. Among various design strategies, through-space charge transfer (TSCT) systems offer the potential for enhanced performance. However, the relationship between molecular configuration and TSCT properties remains unclear compared to traditional through-band charge transfer materials. In this study, we investigated the influence of spatial configuration on TSCT features and electronic properties of triplet excited states in these TSCT materials. By manipulating the spatial arrangement between donor and acceptor segments using different spiro skeletons, a series of TSCT materials (DMB2-DMB5) was synthesized. Together with the parent molecule, DM-B, these materials exhibited completely different TADF characteristics, demonstrating the impact of spatial arrangements on their optoelectronic properties. Thus, the external quantum efficiency of these materials ranged from as high as 28.0 % (DMB2) to as low as 3.6 % (DMB5) due to variations in their TADF characteristics. Our findings highlight the significance of spatial configuration, beyond distance alone, in influencing TSCT properties when donor and acceptor segments are sufficiently close. This insight provides valuable guidance for developing advanced TSCT materials and advancing TADF systems with improved performance and functionality.

Two thermal activation processes, anti-Stokes photoluminescence and delayed fluorescence bolster in crystalized DPQ-DPAC. The organic crystals demonstrate dual capabilities of hot band absorption with a notable 0.1 eV anti-Stokes shift emission and efficient thermally activated delayed fluorescence performance. Conformational changes of the crystalized DPQ-DPAC molecule are identified for such properties.

Abstract

Thermal activation process utilizes environmental thermal energy to help supplement energy for the nonspontaneous energy-consuming upconversion physical transitions with positive free energy change (ΔG>0). Reverse intersystem crossing (rISC) and hot band absorption are two kinds of thermal activation transitions. Thermally activated delayed fluorescence (TADF) materials with rISC have significantly propelled advancements in organic semiconductors. Hot band absorption, enables anti-Stokes photoluminescence, offering a promising route for efficient photon upconversion. In this work, we constructed a crystal consisting of a donor-acceptor type TADF molecule, DPQ-DPAC, demonstrating dual thermal activation properties of hot band absorption with a notable 0.1 eV anti-Stokes shift emission and proficient TADF performance. Only in the crystal TADF efficiency facilitates and the photoluminescence quantum yield elevates to an impressive 90.8 %. Combining the extended absorption spectrum, these enhancements collectively realize anti-Stokes photoluminescence in crystal. Experimental and theoretical results on the DPQ-DPAC crystal indicate optimizations in its conformational and vibrational modes, resulting in enhancements to its properties. This finding provides insight into crafting organic materials with thermally activated functionalities and contributes to fully exploiting the potential of organic materials, further advancing versatile materials applications.

Terminal fluorination enhances crystallinity and J-aggregate ratio of the non-fused ring electron acceptor TBT-V-F, surpassing its chlorinated version. Thus, TBT-V-F-based organic photodetectors exhibit suppressed nonradiative energy loss and more ordered active layer morphology, leading to an ultralow dark current density of 7.30×10^-12 A cm⁻² and exceptional detectivity over 10¹³ Jones in 320–920 nm wavelength, along with excellent stability.

Abstract

High dark current density (J _d) severely hinders further advancement of near-infrared organic photodetectors (NIR OPDs). Herein, we tackle this grand challenge by regulating molecular crystallinity and aggregation of fully non-fused ring electron acceptors (FNREAs). TBT-V-F, which features fluorinated terminals, notably demonstrates crystalline intensification and a higher prevalence predominance of J-aggregation compared to its chlorinated counterpart (TBT-V-Cl). The amalgamation of advantages confers TBT-V-F-based OPDs with lower nonradiative energy loss, improved charge transport, decreased energetic disorder, and reduced trap density. Consequently, the corresponding self-powered OPDs exhibit a 40-fold decrease in J _d, a remarkable increase in detectivity (D*_sh), faster response time, and superior thermal stability compared to TBT-V-Cl-based OPDs. Further interfacial optimization results in an ultra-low J _d of 7.30×10^-12 A cm⁻² with D*_sh over 10¹³ Jones in 320–920 nm wavelength and a climax of 2.2×10¹⁴ Jones at 800 nm for the TBT-V-F-based OPDs, representing one of the best results reported to date. This work paves a compelling material-based strategy to suppress J _d for highly sensitive NIR OPDs, while also illustrates the viability of FNREAs in construction of stable and affordable NIR OPDs for real-world applications.

Utilizing a synergistic π-extension and peripheral-locking strategy, we constructed a high-order B/N-based pure-green MR-TADF emitter via a lithium-free synthetic approach. The associated device achieved narrowband emission with a full width at half maximum (FWHM) of 20 nm, CIE coordinates of (0.18, 0.74), a maximum external quantum efficiency (EQE) of 36.6 % with minimal efficiency roll-off, and a lifetime (LT₈₀) of 485 hours at an initial luminance of 1000 cd m⁻².

Abstract

Multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters offer natural advantages for creating power-efficient, wide-color-gamut OLEDs. However, current green MR-TADF emitters face challenges in simultaneously achieving high color purity and efficient reverse inter-system crossing (RISC), leading to suboptimal device performance. In this study, we propose a synergistic molecular design approach that combines π-extension and peripheral locking to address these challenges. This approach allows for the construction of quadruple borylated MR-TADF emitters that not only deliver precisely tuned pure-green emission with a narrow full width at half maximum (FWHM) of 15 nm, but also exhibit close-to-unity quantum yield, rapid RISC, and optimal horizontal dipole orientation. The resulting sensitizer-free OLED approaches the BT.2020 standard with CIE coordinates of (0.18, 0.74) and demonstrates impressive external quantum efficiency (EQE) of 36.6 % at maximum and 31.8 % at 1000 cd m⁻². Additionally, the device shows good operational stability, with a lifetime (LT₈₀) of 485 hours at an initial luminance of 1000 cd m⁻². This study hence offers a promising molecular design strategy that effectively enhances the comprehensive OLED performance.

Multimodal upconversion/downshifting circularly polarized luminescence (CPL), covering a broad emission range from ultraviolet (UV) to the second near-infrared (NIR-II) region, has been realized within a single nanoparticle. This approach enables cutting-edge encryption applications, including optical anticounterfeiting and information encryption.

Abstract

Multimodal upconversion and downshifting circularly polarized luminescent materials hold significant potential for optical anticounterfeiting applications due to their exceptional chiroptical properties. However, constructing these materials within a single emitter remains challenging. In this study, a conceptual model of multimodal upconversion/downshifting circularly polarized luminescence (CPL) is realized within a single nanoparticle. A new type of nanoparticles with multilayer core–shell architecture is fabricated, capable of delivering upconversion/downshifting luminescence, when excited by a 980 nm laser. Utilizing a co-assembly strategy, multimodal upconversion/downshifting CPL emission, covering a broad emission range from ultraviolet (UV) to the second near-infrared (NIR-II) region, can be realized at the supramolecular level. These chiroptical properties closely follow the chirality of host matrix and are strongly dependent on the distribution mode of nanoparticles within the matrix films. The multimodal upconversion/downshifting CPL behavior enabled cutting-edge encryption applications including optical anticounterfeiting and information encryption. This work introduces a novel approach to designing multimodal upconversion/downshifting CPL materials and opens new avenues for the development of chiroptical functional materials.

By delicately rebuilding peripheral F, Cl, Br footprints, the central brominated acceptor of CH−B afforded the first-class efficiency of 19.78 % for binary organic solar cells, also achieved the best performance when further increasing active layer thickness to ~300 nm.

Abstract

Given homomorphic fluorine (F), chlorine (Cl) and bromine (Br) atoms are featured with gradually enlarged polarizability/atomic radius but decreased electronegativity, the rational screen of halogen species and locations on small molecular acceptors (SMAs) is quite essential for acquiring desirable molecular packing to boost efficiency of organic solar cells (OSCs). Herein, three isomeric SMAs (CH−F, CH−C and CH−B) are constructed by delicately rebuilding peripheral F, Cl, Br footprints on both central and end units. Such a re-permutation of peripheral halogens could not only maintain the structural symmetry of SMAs to the maximum, but also acquire extra asymmetric benefits of enhanced dipole moment and intramolecular charge transfer, etc. Moreover, central brominating enhances molecular crystallinity of CH−B without introducing undesirable steric hindrance on end groups, thus rendering a better balance between high crystallization and domain size control in PM6:CH−B blend. Further benefitting from the large dielectric constant, small exciton binding energy, optimized molecular packing and great electron transfer integral, CH−B affords the first class binary OSC efficiency of 19.78 %, moreover, the highest efficiency of 18.35 % thus far when increasing active layer thickness to ~300 nm. Our successful screening in rebuilding peripheral halogen footprints provides the valuable insight into further rational design of SMAs for record-breaking OSCs.

We have demonstrated a new approach of ΔE _ST modulation via the triplet blocking effect, achieving decreased S₁ but constant T₁ energy level. The conflict between small ΔE _ST and large oscillator strengths is relieved. The results are crucial for fundamental photophysics as well as development of optoelectronic materials.

Abstract

Thermally activated delayed fluorescence (TADF) molecules have been widely investigated in organic light emitting diodes (OLED), organic lasing, etc. Small singlet-triplet energy gap (ΔE _ST) and high radiative rate constants (k _F) are highly desired to utilize triplet excitons efficiently and are beneficial to reduce efficiency roll-off of devices of OLED devices. The prevalent TADF molecules are via donor-acceptor molecular design, for which the decreasing of the ΔE _ST is often at the expense of reducing the k _F. Herein, we demonstrated a new ΔE _ST modulation approach to construct TADF with high k _F, based on triplet blocking effect, i.e., the extension of π-conjugation of a triplet constrainer (IB) leads to a gradually red-shifted S₁ but a constant T₁ energy and therefore reduced ΔE _ST controlled from monomer (IB), monomer-linker (IB-BF₂ ), to dimer of IB-BF₂-IB. The natural transition orbital analysis indicates that S₁ state is delocalized while T₁ state is localized as confirmed by time resolved electron paramagnetic resonance spectroscopy. Therefore, the ΔE _ST is reduced from 0.60 eV, 0.46 eV to 0.25 eV, while keeping faster radiation rate (around 10⁸ s⁻¹) than that of conventional donor-acceptor molecules (10⁶∼10⁷ s⁻¹). As a result, the emission mechanisms are regulated from fluorescence for IB, phosphorescence/TADF dual emissions for IB-BF₂ to TADF for IB-BF₂-IB. This paper proposed a new approach of ΔE _ST modulation and a new type of TADF molecule with high radiation rate, which is crucial for fundamental photophysics as well as material science.

Chirality-assisted synthesis is used to create chiral and enantiopure annulated nanobelts from their chiral precursors via a one-pot self-condensation process in 84 % yield.

Abstract

Shape-persistent conjugated nanobelts (CNBs) are fascinating synthetic targets. However, in most cases these are made in low overall yields by applying strategies of macrocyclization followed by (multiple) ring fusion reactions for nanobelt formation. Here, we describe the high yielding synthesis of enantiopure chiral nanobelts in 84 % yield by applying chirality-assisted synthesis (CAS). The chiral nanobelts were investigated by UV/Vis and CD spectroscopy. By DFT calculations the aromaticity of these structures is discussed.

Circularly polarized organic room-temperature phosphorescence (CPP) is essential in chemistry and materials-related fields. This Review summarizes the latest advances in organic CPP from the molecule to the supramolecular assembly scales, focusing on design strategies such as chirality transfer, assembly-induced chirality amplification, and chiral superstructure-mediated transmission. Remaining challenges and an insightful outlook are also presented.

Abstract

Organic circularly polarized luminescence (CPL) plays crucial roles in chemistry and biology for the potential in chiral recognition, asymmetric catalysis, 3D displays, and biological probes. The long-lived luminescence, large Stokes shift, and unique chiroptical properties make organic circularly polarized room-temperature phosphorescence (CPP) a new research hotspot in recent years. Nevertheless, achieving high-performance organic CPP is still challenging due to the sensitivity and complexity of integrating triplet excitons and polarization within organic materials. This review summarizes the latest advances in organic CPP, ranging from design strategies and photophysical properties to underlying luminescence mechanisms and potential applications. Specifically, the design strategies for generating CPP are systemically categorized and discussed according to the interactions between chiral units and chromophores. The applications of organic CPP in organic light-emitting diodes, sensing, chiral recognition, afterglow displays, and information encryption are also illustrated. In addition, we present the current challenges and perspectives on developing organic CPP. We expect this review to provide some instructive design principles to fabricate high-performance organic CPP materials, offering an in-depth understanding of the luminescence mechanism and paving the way toward diverse practical applications.

A strategy based on carbon locking and sulfur embedding has been used to construct a high-performance red multiple resonance (MR) emitter. The fabricated organic light-emitting diode (OLED) based on the target molecule exhibits Commission Internationale de l’Éclairage coordinates of (0.67,0.33) and a record-high power efficiency of 50.1 lm W⁻¹.

Abstract

The discovery of multiple resonance thermally activated delayed fluorescence (MR-TADF) materials with remarkable narrowband emission has opened a new avenue for the development of organic light-emitting diodes (OLEDs) with high color purity. However, the lack of construction strategies for purely red MR-TADF materials significantly impedes their application in full-color high-definition displays. Herein, we propose a unique and handy approach of spiro-carbon-locking and sulfur-embedding strategy to modify the parent MR-TADF framework, resulting in a red MR-TADF emitter with high color purity. The reported MR-TADF molecule (namely, FSBN) demonstrates a pure red emission with an emission maximum of 621 nm in toluene solution. The OLED with FSBN as emitter exhibits Commission Internationale de l’Éclairage (CIE) coordinates of (0.67, 0.33), which exactly matches the red standard defined by the National Television Standards Committee (NTSC). Importantly, the single-host OLED achieves a high power efficiency (PE) of up to 50.1 lm W⁻¹, suggesting the potential for the development of low power consumption red OLEDs.

A novel host-guest system, wherein TPP-4C-BI is doped into TPP-4C-Cz crystals, is experimentally shown to enhance room-temperature phosphorescence quantum yields 10-fold. Groundbreaking visualization of typically undetectable guest molecules is achieved for the first time within the host crystal structure. Single crystal X-ray diffraction reveals a unique “sergeant-and-soldier” effect, where the guest molecules control the conformations of the host, significantly influencing crystal packing. This system also exhibits efficient triplet-triplet energy transfer from host to guest, promoting improved radiative decay.

Abstract

Host-guest systems have emerged as an efficient strategy for promoting organic room temperature phosphorescence (RTP). Despite the advantages of doping guest molecules into a host matrix, the complexity of these systems and the lack of techniques to visualize host-guest interactions at the molecular scale pose significant challenges in understanding the underlying mechanisms. Here, a novel host-guest RTP system is developed by incorporating low concentrations (1–10 mol%) of TPP-4C-BI (guest) into crystalline TPP-4C-Cz (host). Utilizing structural isomerism, the guest molecules are regularly incorporated into the host crystal lattice, resulting in phosphorescence quantum yields almost ten times higher than the pure compounds. The system enabled resolution of the molecular packing of the single crystal through X-ray diffraction, providing unprecedented visualization of host-guest interactions. A “sergeant-and-soldier” effect, where the minority dopant molecules (sergeants) significantly influence the packing arrangement of the host molecules (soldiers), enhances RTP is identified. Further analyses revealed that due to the host molecule's inefficient phosphorescence pathway, its long-lived dark triplets are channeled to the guest via triplet-triplet energy transfer (TTET), allowing the excited energy to radiatively decay more efficiently. These insights advance the understanding of RTP mechanisms and offer practical implications for designing high-efficiency phosphorescent materials.