Rong-Huei Yi

Engineering localized aromaticity in amine-embedded polycyclic aromatic hydrocarbons effectively suppresses molecular vibration coupling and reduces the intensity of shoulder peaks in emission spectra, thereby giving rise to highly efficient yellow and red narrowband fluorophores for the assembly of high-performance organic light-emitting diodes.

Abstract

The development of narrowband fluorescent emitters remains a long-standing challenge in organic optoelectronics. Herein, we present an aromaticity engineering approach based on a perylene core to construct highly efficient narrowband fluorescent emitters. Replacement of one naphthalene unit with a carbazole moiety enhances the localization of aromaticity, while extension of the π–conjugation further attenuates the aromaticity of the remaining naphthalene ring. This dual modulation effectively suppresses emission shoulder bands, yielding spectrally pure fluorescence. Consequently, the centrosymmetric c-NaDTCz and the axially symmetric a-NaDTCz exhibit sharp emissions at 536 and 600 nm, with narrow full widths at half-maximum (FWHM) of 17 and 30 nm, respectively. When applied in OLEDs, the c-NaDTCz-based device displays sharp yellow emission peaking at 548 nm with a high external quantum efficiency (EQE) of 26.1%, while a-NaDTCz delivers narrowband red electroluminescence at 610 nm, achieving a record-high EQE of 27.8% for conventional red fluorescent emitters.

Through a chiral space conjugation strategy, a highly efficient chiral multi-resonant thermally activated delayed fluorescence emitter incorporating the [2.2]paracyclophane unit is prepared, realizing strong chiroptical responses with absorption dissymmetry factor over 0.02 and pure green emission with Commission Internationale de I’Éclairage y coordinate of 0.70. Furthermore, highly efficient circularly polarized organic light-emitting diodes with remarkable luminance of 241k cd m⁻², external quantum efficiency over 29% and ideal efficiency roll-off are achieved.

Abstract

Developing thermally activated delayed fluorescence (TADF) materials with excellent chiroptical and photophysical properties is crucial for advancing optoelectronic applications. Herein, a chiral space conjugation strategy incorporating a typical [2.2]paracyclophane unit is proposed to construct a highly efficient chiral multi-resonant (MR) TADF emitter, R(S)-PCP-DBNO. Guided by the symmetry-matching rule, the molecular design achieves balanced contribution and optimal alignment of transition electric and magnetic dipole moments, resulting in a strong chiroptical response with a dissymmetry factor (|g _abs|) exceeding 0.02. Meanwhile, owing to the special through-space conjugation, the enantiomer exhibits pure green emission with a peak at 526 nm, a narrow full-width at half-maximum of 26 nm, a Commission Internationale de I’Éclairage y coordinate of 0.70 and a quantum efficiency of 0.94 in toluene solution. When integrated into sensitized organic light-emitting diodes (OLEDs), R(S)-PCP-DBNO delivers a maximum luminance up to 241k cd·m⁻², a maximum external quantum efficiency up to 29.4% and minimal efficiency roll-off. Furthermore, the devices demonstrate distinct circularly polarized electroluminescence, confirming the utility of this strategy for chiral MR-TADF emitters and circularly polarized OLEDs with simultaneous color purity, efficiency, and chiroptical functionality.

A circularly polarized multiple resonance thermally activated delayed fluorescence (CP-MR-TADF) molecular engineering composed of discontinuous fused benzene rings is proposed, and obtains a pair of green BN[7]helicene-based emitters (P/M)-DBN-mICz. (P) and (M)-DBN-mICz-based electroluminescence devices deliver pure-green emission peaking at 516 nm, with Commission Internationale de L'Eclairage (CIE) coordinates of (0.17, 0.72), electroluminescence dissymmetry factors (g _ELs) of +5.3 × 10⁻³/−8.5 × 10⁻³ and maximum external quantum efficiencies (EQEs) of 37.3%/36.6%, respectively.

Abstract

Helicene-based circularly polarized luminescence (CPL) materials suffer from severely low color purity in circularly polarized organic light-emitting diodes (CP-OLEDs). Here, a novel molecular engineering strategy is introduced by replacing helicene containing continuous fused benzene rings with a multiple resonance (MR) framework comprising discontinuous fused benzene rings. This approach effectively suppresses high-frequency C─C bond stretching vibrations and enhances short-range charge transfer, enabling high color purity, CPL activity, and efficient thermally activated delayed fluorescence (TADF). The proof-of-concept green BN[7]helicene-based emitters (P/M)-DBN-mICz display bright and narrowband green emission peaking at 512 nm with a full-width at half-maximum (FWHM) of 25 nm. Notably, the enantiomers (P)- and (M)-DBN-mICz exhibit narrowband CPL spectra with FWHMs of 26 and 25 nm, the Commission Internationale de l'Éclairage (CIE) coordinates of (0.14, 0.72) and (0.15, 0.72), and photoluminescence dissymmetry factors of +2.3 × 10⁻³ and −2.6 × 10⁻³. (P)- and (M)-DBN-mICz-based CP-OLEDs deliver pure-green emission, characterized by a peak wavelength of 516 nm, a narrow FWHM of 27 nm, and CIE coordinates of (0.17, 0.72), representing the purest green CP-OLEDs reported to date. Furthermore, these devices exhibit high electroluminescence dissymmetry factors of +5.3 × 10⁻³/−8.5 × 10⁻³, and maximum external quantum efficiencies of 37.3% and 36.6%, respectively.

Increasing aromaticity in a series of selenium-embedded hetero rings stabilizes the emitter while exploits the advantages of heavy atoms effect, which results in narrowband pure-green OLEDs with high efficiency, reduced roll-off and long device lifetime.

Abstract

The development of high-performance organic light-emitting diodes (OLEDs) that simultaneously achieve narrowband emission, superior efficiency, and extended operational stability remains a significant challenge for thermally activated delayed fluorescent (TADF) materials. Herein, a novel molecular architecture is reported that strategically integrates selenium (Se) into a rigid pentagonal aromatic sextet (dibenzoselenophene, DBSe) within a multi-resonance (MR) framework, addressing the intrinsic limitations of hexagonal Se-MR systems. The developed molecule DBSe-BN exhibits a rapid reverse intersystem crossing (RISC) rate in the order of 10⁶ s⁻¹ and narrow emission bandwidth of 21 nm, providing persuasive guarantee for high-performance pure-green emission. Notably, the DBSe-BN-based OLEDs demonstrate exceptional performance, including a high maximum external quantum efficiency (EQE_max) of 38.8%, suppressed efficiency roll-off (EQE₁₀₀₀ = 33.7%), and pure-green emission, characterized by Commission Internationale de l'Eclairage (CIE) coordinates of (0.18, 0.73). The devices exhibit remarkable operational stability, with greatly prolonged lifetime (LT₅₀) of 1341 h based on binary-emitting system and 5310 h based on the ternary device, at an initial luminance of 1000 cd m⁻². This work presents a feasible strategy for gathering high-performance MR-TADF emitters, achieving a multi-dimensional balanced OLED with enhanced FWHM, CIE, EQE, roll-off and lifetime promoted by Se-embedded aromatic sextet.

A pair of B,N-hetero[8]helicene (P/M-BN8H) with MR-TADF feature are obtained by embedding one aza-heptagon heterocycle unit into helical skeleton. With the chiral helicene as emitter, high-performance CP-OLED is fabricated featuring narrowband (FWHM = 37 nm) and efficient CPEL property with maximum external quantum efficiency of up to 30.0%.

Abstract

Helicene-based emitters for high-efficiency circularly polarized organic light-emitting diodes (CP-OLEDs) still present several unresolved challenges of suboptimal color purity in higher-ordered helicenes and serious efficiency roll-off. Herein, a pair of chiral [8]helicenes (P/M-BN8H) are successfully constructed by fusing B,N-embedded polycyclic aromatic hydrocarbon with carbazole and indolocarbazole units via an aza-heptagon heterocycle. The strategy of incorporating twisted heterocycles effectively modulates both the electronic structure and geometric configuration of the helicene backbone. This approach simultaneously suppresses intermolecular interactions while preserves the intrinsic multiple resonance thermally activated delayed fluorescence characteristics of the target molecule. Moreover, the presense of aza-heptagon heterocycle promotes spin-orbit coupling between the locally excited triplet states and the simple state, facilitating the reverse intersystem crossing process thereby suppressing efficiency roll-off. Furthermore, the π-extended [8]helicene conjugation structure effectively stabilizes the chiral configuration, enabling helical enantiomer robust circularly polarized luminescence properties. The CP-OLEDs fabricated with P/M-BN8H achieved narrowband emission with a small full width at half maximum of 37 nm and a maximum external quantum efficiency of up to 30.0% with low efficiency roll-off, and also demonstrated significant circularly polarized electroluminescence signals.

A spatially compacted intramolecular design for through-space charge transfer emitter enables narrowband thermally activated delayed fluorescence with fast spin flipping and antiquenching behavior. This approach delivers ultranarrow electroluminescence, achieving a full width at a half-maximum of only 22 nm and a record-setting external quantum efficiency of 27.7% at a display-relevant luminance of 100 nit.

Abstract

Organic fluorophores with through-space donor/acceptor interaction have garnered significant attention for their unique charge transfer properties and advanced applications. However, their use in luminescent applications is hindered by challenges such as low luminescence efficiency, and broad emission spectra. Herein, a series of highly emissive thermally activated delayed fluorophores combining a boron-based multi-resonance acceptor and an arylamine donor within a spatially compacted structure is designed and synthesized. By strategically varying spatial compactness, donor/acceptor interactions are fine-tuned, enabling precise control over high-lying excited states with charge transfer characteristics while preserving narrow-spectrum thermally activated delayed fluorescence. Key structural optimizations, including a planar acceptor and a space-compacting methyl group, resulted in a highly compact configuration, boosting reverse intersystem crossing rates by over 20-fold compared to the parent fluorophore. This design minimizes concentration-induced quenching and spectral broadening, yielding superior solid-state luminescence. The resulting organic light-emitting diodes achieved ultranarrow electroluminescence (full width at half-maximum of 22 nm) and a remarkable external quantum efficiency of 31.1%, along with reduced efficiency roll-offs.

A robust molecular design strategy for MR-TADF emitters via heterocyclic carbazole integration to strengthen weak C─N bonds was proposed. Blue MR-TADF emitters m-Cz-DABNA and tBu-Cz-DABNA have achieved ultra-narrow FWHMs (24/21 nm), high PLQYs (88%/95%), and record-high EQEs (23%/26%). The tBu-Cz-DABNA OLED achieved LT₉₀ of ∼81 h at 1000 cd m^{− 2} for being among the longest for CIE_y ≤ 0.10 blue OLEDs, approaching BT.2020 coordinates.

Abstract

The development of efficient and stable ultra-narrowband pure-blue multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters is critical for next-generation wide-gamut OLED displays. Herein, we present a molecular design strategy that enhances emitter stability and efficiency by reinforcing the weak C─N bonds through selective incorporation of heterocyclic carbazole (Cz) units into the MR framework. Two proof-of-concept emitters, m-Cz-DABNA and tBu-Cz-DABNA, were synthesized via high-yield, lithium-free borylation. These emitters exhibit pure-blue emissions at 453 and 463 nm with narrow full-width at half-maximums (FWHMs) of 24 and 21 nm in solution and high photoluminescence quantum yields (PLQYs) of 88% and 95%, respectively. OLED devices based on m-Cz-DABNA and tBu-Cz-DABNA show emissions at 456 nm (FWHM 24 nm, EQE_max 23%, CIEy 0.06) and 467 nm (FWHM 24 nm, EQE_max 26%, CIEy 0.10), respectively, holding among the highest efficiencies for blue OLEDs without sensitizers. Notably, the tBu-Cz-DABNA-based device shows an LT₉₀ of ∼81 h at 1000 cd m^{− 2} (EQE 8.95%), representing one of the longest operational lifetimes for blue fluorescent OLEDs with CIEy ≤ 0.10. These results demonstrate a versatile and scalable molecular design strategy for the realization of high-efficiency, long-lifetime blue OLEDs approaching the BT.2020 color standard.

Nature Photonics, Published online: 08 September 2025; doi:10.1038/s41566-025-01729-7

This study presents a stereochemically controlled synthesis of [9]cycloparaphenylene-pillar[5]arene trimers using a social chiral self-sorting strategy with a triangular gold complex. This selective synthesis is attributed to the dynamic reorganization of Au─C σ-bonds, specific conformations of phosphine ligands, and inter-pillararene interactions.

Abstract

The precise synthesis of stereochemically controlled multicavity macrocyclic hosts based on pillar[n]arenes presents a significant challenge in supramolecular chemistry. This difficulty primarily stems from the spontaneous generation of planar chirality-induced stereoisomer mixtures during synthetic procedures, which considerably complicates the isolation process. In this study, we introduce a social chiral self-sorting strategy utilizing a triangular gold complex, enabling the stereochemically controlled synthesis of [9]cycloparaphenylene-pillar[5]arene trimers ([9]CPP-3P[5]A). Diverging from conventional synthetic approaches that typically yield four stereoisomers of pillararene trimers ( pSSS , pRRR , pSSR , and pRRS ), our methodology demonstrates selectivity, predominantly generating pSSR and pRRS isomers of [9]CPP-3P[5]A, with only trace amounts of pSSS and pRRR isomers. This stereoselectivity, as elucidated by crystallographic analysis, arises from the dynamic reorganization of Au─C σ-bonds during the assembly of the hexagold(I) complex, synergistically combined with specific phosphine ligand conformations and inter-pillararene interactions. The resulting chiral trimers exhibit circularly polarized luminescence (CPL) properties, which facilitates the fabrication of CPL-active supramolecular polymers by leveraging the superior host–guest complexation capability of the pillar[5]arene units, opening new avenues for the development of chiral functional materials.

We report a novel chiral biphenyl-based single molecule emitter, CP-D3, with both thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) emissions, achieving the maximum external quantum efficiency (EQE_max) of 32.44% in circularly polarized organic light-emitting diodes (CP-OLEDs). This represents the first report of a chiral single-molecule emitter incorporating a biphenyl component that exhibits simultaneous TADF and RTP emissions, as well as highly efficient CP-OLEDs.

Abstract

Chiral single molecules that exhibit both thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) pose significant challenges, primarily due to their competitive luminescence mechanisms and the scarcity of studies on their applications in circularly polarized organic light-emitting diodes (CP-OLEDs). In this work, we develop a novel chiral emitter, CP-D3, with an axially chiral biphenyl segment selected as the chiral center. As a result, CP-D3 successfully exhibits both TADF and RTP properties with a high photoluminescence (PL) efficiency of 91%. The high dissymmetry factors (g _CPPL) of −7.98 × 10⁻³ and +7.47 × 10⁻³ are obtained for (R/S)-CP-D3, respectively. Notably, the CP-D3-based CP-OLEDs achieve a maximum external quantum efficiency (EQE_max) of 32.44%, which represents the highest value among chiral luminance materials based on an axially chiral biphenyl component. The g _CPEL is recorded as −8.13 × 10⁻⁴/+5.92 × 10⁻⁴ for (R/S)-CP-D3-based CP-OLEDs. This work presents the first report on a chiral single-molecule emitter incorporating an axially chiral biphenyl component, which exhibits simultaneous TADF and RTP emissions and enables highly efficient CP-OLEDs.

A promising strategy by orthogonal engineering of achiral blue thermally activated delayed fluorescence (TADF) emitters and chiral orange assemblies was proposed to fabricate white circularly polarized organic light-emitting diodes (CP-OLEDs). This strategy leverages the high exciton utilization and chiral amplification, yielding a record g _EL of 0.34 and EQE_max of 6.3%. This work represented the state-of-the-art white CP-OLEDs, delivering the highest reported combination of external quantum efficiency (EQE) and g _EL to date.

Abstract

The development of white circularly polarized organic light-emitting diodes (CP-OLEDs) faces a critical challenge in simultaneously achieving high external quantum efficiency (EQE) and large dissymmetry factors (g), due to the inherent trade-off between exciton utilization and chirality amplification. Herein, we propose an orthogonal architecture synergizing an achiral blue thermally activated delayed fluorescence (TADF) emitter with chiral orange assemblies to overcome this limitation. The chiral assemblies, featuring exceptional chiroptical activity (|g _abs| = 0.95 and |g _lum| = 0.85), are engineered as both photon-selective filters and emitters. When integrated with a blue TADF layer, this dual-layer design enables 100% internal quantum efficiency through TADF-enabled triplet harvesting and chiral amplification via selective absorption of blue photons with a specific polarization direction, generating amplified white circularly polarized electroluminescence (CPEL). The resulting white CP-OLED (CIE: 0.31, 0.34) achieves a record |g _EL| of 0.34 alongside an EQE_max of 6.3%, demonstrating the unprecedented white CP-OLEDs when considering both EQE and g _EL values. By optimizing the TADF doping ratio, a cool-white CP-OLED is realized with an EQE of 14.7% and |g _EL| of 0.32. This work establishes a material orthogonal engineering to decouple exciton-chirality interdependencies, opening avenues for fabricating high-performance CPEL devices.

π-Conjugated chiral macrocycles with reversible photoregulatable chiroptics (|g _abs|: 0.023↔0.014; CPL ON/OFF) and cave sizes (e.g., 25.8 × 19.8 Å ↔ 22.6 × 18.3 Å) were firstly synthesized, which do not exist in previously documented π-conjugated chiral macrocycles. Continuous chirality amplification was realized, giving high dissymmetry factors (|g _abs| = 0.023, |g _lum| = 0.013). A size-photoswitching correlation was revealed innovatively.

Abstract

Chiral macrocycles have attracted considerable attention because of their fascinating circular chiral topologies, circularly distributed electronic structures, and excellent chiroptical features. However, the challenging synthesis and limited cases hinder the understanding, improvement, and regulation of their optoelectronic properties. To avoid this dilemma, we employed cyclic Suzuki–Miyaura coupling between dithienylethene (DTE) and [6]helicene to firstly synthesize donor–acceptor (D–A)-type π-conjugated chiral macrocycles, including m-[1 + 1], m-[2 + 2], and m-[3 + 3], where these compounds displayed photocontrollable ring sizes and chiroptical properties. More importantly, continuous amplification in chirality can be achieved via distinctive multiple chiral-centers-bonding in series within helical rings, giving high |g _abs| and |g _lum| of up to 0.023 and 0.013, respectively. The macrocycles were endowed with a photoswitchable function that is absent in previously documented π-conjugated chiral macrocycles. Both the cavity sizes and chiroptical properties could be photoregulated. As typical examples, the cavity dimension of m-[3 + 3]-PPP was photoadjusted from 25.8 × 19.8 to 22.6 × 18.3 Å, accompanied by reversible photoswitched |g _abs| between 0.023 and 0.014 and remarkable CPL ON/OFF behavior. Moreover, a size-photoswitching correlation was revealed innovatively, i.e., the photoswitching ability increased with increasing ring size. Our study provides a new guidance for developing high-performance chiral systems and novel stimuli-responsive chiral macrocycles and provides ideal platforms for understanding chiral structure–functionality relationships.

Reversible switching between room temperature phosphorescence and delayed fluorescence is achieved through solid-liquid phase transitions in donor-acceptor systems, where tunable molecular conformation of the N-phenylphenoselenazine donor unit governs luminescence mode switching. This finding establishes a new approach for stimuli-responsive luminescent materials.

Abstract

Switching between triplet-involved room temperature phosphorescence (RTP) and delayed fluorescence (DF) is pivotal for advancing molecular encryption application but remains a significant challenge in multicomponent material systems. In this study, we successfully realized the selective modulation of RTP and DF emissions in a donor-acceptor doping system by inducing conformational changes in the donor through solid-liquid transition. In the solid state, the donor adopts a highly twisted quasi-axial conformation, which effectively suppresses non-radiative decay, resulting in efficient green RTP. In contrast, in the liquid state, the donor transitions to a relatively planar conformation, forming the intermolecular charge transfer state with the acceptor, significantly reducing the energy gap between the lowest singlet and triplet excited states, thereby facilitating reverse intersystem crossing (RISC) and generating yellow DF. Furthermore, the coexistence of multiple emissive triplet states demonstrates promising applications in information encryption, ink-free rewritable paper, and thermal sensing.

The supramolecular polymerization of enantiopure triarylamine trisamide monomers bearing aggregation-induced emissive tetraphenylethene units, gave rise to a strong circularly polarized luminescence (with g _lum values as high as |1.8·10⁻²|). Strikingly, upon fast versus slow cooling rates, these monomers formed distinct hierarchical self-assemblies (i.e., (P)-helices versus (M)-superhelices) that emitted circularly polarized light of opposite handedness.

Abstract

The supramolecular polymerization and chiroptical properties of two enantiopure triarylamine trisamide (TATA) monomers bearing aggregation-induced emissive tetraphenylethene (TPE) units are described. A monosubstituted and a trisubstituted monomer were synthesized and their self-assembly was investigated upon either fast or slow cooling of chlorobenzene solutions. Depending on the cooling rate, two distinct fluorescent self-assemblies of opposite supramolecular chiralities were obtained from each monomer. Both the TATA and the TPE units were found to play important roles in the self-assembly process and chiroptical properties. Remarkably, the self-assembly of the monosubstituted monomer gave rise to a strong circularly polarized luminescence originating from the TATA core (g _lum values as high as |1.8·10⁻²| in solution) with opposite cooling-rate-dependent handedness.

New linear and bent tetra-N-fused indolocarbazole isomers (l-N4ICz and s-N4ICz) exhibited distinct photophysical properties and device performance, with l-N4ICz-based devices achieving pure green emission characterized by a full width at half maximum of 19 nm, a CIEy coordinate of 0.7, a high external quantum efficiency of 30.1%, and minimal efficiency roll-off.

Abstract

Developing efficient narrowband emitters beyond the blue region remains challenging for indolocarbazole-based multiple resonance (ICz-MR) systems, primarily due to the inherent trade-off between spectral red-shifting and linewidth broadening. To address this, we pioneer tetra-N-fused ICz isomers (l-N4ICz and s-N4ICz) with four consecutive para-positioned nitrogen atoms, forming extended π-systems via alternating six-/five-membered ring fusion. The linear isomer l-N4ICz achieves sharp green photoluminescence peaking at 506 nm with a full width at half maxima (FWHM) of merely 14 nm—surpassing the bent analogue—alongside suppressed spectral shoulders and higher photoluminescence efficiency. Theoretical studies reveal the critical role of orbital symmetry engineering of adjacent segments in governing the optoelectronic properties of isomers. Organic light-emitting diodes with l-N4ICz deliver pure-green electroluminescence with an ultra-narrow FWHM of 19 nm and the first chromaticity y-coordinate reaching 0.7 among ICz-MR systems, alongside a peak external quantum efficiency of 30.1%, which remains at >20% even under extremely high luminance over 200 000 cd m⁻². The same device also sets a benchmark long operational lifetime of 2327 h to decay to 90% of the initial luminance of 1000 cd m⁻². These findings highlight the great potential of multi-N-fused ICz-MR structures for highly efficient, stable, and narrow electroluminescence.

Amplified spontaneous emission (ASE) in difluoroboron-based gain molecules is shown to originate from aggregated singlet states (S₁), contradicting its previously assumed phosphorescent origin. Additionally, the delayed emission arises from a triplet–triplet annihilation upconversion (TTA-UC) mechanism rather than a thermally activated (TADF) process, with rapid photodegradation further complicating the excited-state dynamics and emphasizing the need for improved molecular design.

Abstract

In this study, we investigate the triplet exciton dynamics of a series of difluoroboron-based organic gain molecules. We synthesized three previously reported molecules from the difluoroboron family and examined their photophysical properties using time-resolved emission spectroscopy and high-level theoretical calculations. Our results reveal that emission from these materials arises predominantly from the singlet manifold via prompt and triplet–triplet annihilation (TTA)-driven delayed fluorescence, rather than from phosphorescence, challenging the earlier assumptions of amplified spontaneous emission (ASE) originating from the triplet manifold. In highly concentrated solutions, the emission shows strong resemblance to that of the crystalline phase, confirming its origin from aggregate singlet states rather than monomeric pathways. Further, the materials are prone to photodegradation, which gives rise to new high-energy fluorescence and phosphorescence bands adding to the complexity of the photophysics of this family of materials.

A new family of (2,5,4)-trapeziumenes bearing NBNBN, NBOBN, OBNBO, and OBOBO doping patterns is synthesized. Progressive N→O substitution enables precise control over the excited-state landscape, increasing the S₁ energy, decreasing the T₁ energy, and widening the T₂–T₁ energy gap.

Abstract

The rational design of polycyclic aromatic hydrocarbons that combine chemical and physical robustness with finely tuned optoelectronic properties remains a key challenge in materials science. As an initial step toward this goal, we report the synthesis and comprehensive characterization of a new class of boron-, nitrogen-, and oxygen-doped peri-acenoacenes, termed (2,5,4)-trapeziumene congeners. Analysis of these systems provides chemical descriptors that could guide the rational tailoring of their properties through peripheral doping. The target trapeziumene congeners were obtained via a sequence of Suzuki–Miyaura and Buchwald–Hartwig couplings, followed by directed borylation, giving both phenylborane and borinic derivatives with diverse peripheral doping sequences. Single-crystal X-ray diffraction revealed planar to slightly twisted backbones, with peripheral heteroatomic motifs that modulate π-conjugation and intermolecular packing. Photophysical studies showed bright fluorescence (Φ _F up to 0.99), narrow Stokes shifts, and structured phosphorescence at 77 K. Electrochemical analysis demonstrated p-type behavior and a progressive HOMO–LUMO gap widening upon N→O substitution. Theoretical investigations revealed that N→O substitution asymmetrically affects the excited states, blue-shifting fluorescence while red-shifting phosphorescence, through an asymmetric charge stabilization in the S₁ and T₁ excited states. This is accompanied by a progressive widening of the T₁–T₂ energy gap.

A novel rigid tetradentate Pt(II) emitter (PtCK1) was developed via strategic molecular engineering. Top-emitting PhOLED based on PtCK1 achieved a record-high peak blue index (BI) of 397 cd A⁻¹ CIEy⁻¹ with CIEy < 0.05, meeting the BT.2020 blue color gamut standard.

Abstract

Organic light-emitting diodes (OLEDs) hold great promise for next-generation ultra-high-resolution 4 K/8 K display technologies. However, the development of high-efficiency deep-blue OLEDs based on tetradentate Pt(II) emitters that simultaneously meet the BT.2020 blue color gamut and low efficiency roll-off remains a formidable challenge. In this study, we designed a rigid, narrow-spectrum, deep-blue phosphorescent Pt(II) emitter, PtCK1, by strategic regulation of excited-state properties and incorporation of bulky three-dimensional steric geometry. PtCK1 exhibits excellent photophysical properties, including a small full width at half maximum (FWHM) of 15.6 nm and a high photoluminescence quantum yield of 97%. As a result, PtCK1-bottom-emitting OLED achieves deep-blue emission with a peak at 460 nm, an FWHM of 21 nm, and a maximum external quantum efficiency of 25.3%. Even at luminance levels of 5000 cd m⁻², the EQEs remain as high as 19.3%. Impressively, top-emitting phosphorescent OLED achieves improved color purity, with an ultranarrow spectrum (FWHM = 14 nm), Commission Internationale de l'Éclairage (CIE) coordinates of (0.139, 0.046), fully satisfying the BT.2020 blue standard, and especially a record-high maximum blue index (BI) of 397 cd A⁻¹ CIE_y ⁻¹ with CIE_y < 0.05. This study provides a valuable strategy for developing high-performance tetradentate Pt(II) emitters that meet the BT.2020 blue gamut.

Multi-spiral donor engineering unlocks narrowband thermally activated delayed fluorescence emitters with external quantum efficiency of 39.1% and full-width half-maximum of 25 nm. Orthogonal spiral donors suppress aggregation while boosting efficiency—a leap toward high-performance OLEDs.

Abstract

The pursuit of narrowband multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters with both high efficiency and color purity remains a critical challenge in the field of organic light-emitting diodes (OLEDs). A novel molecular design paradigm is proposed by hybridizing di-/tri-spiral donors in polycyclic heteroaromatic frameworks. The orthogonal, sterically hindered spiral donors disrupt molecular planarity, which can simultaneously suppress the aggregation-caused quenching and spectral broadening. These emitters exhibit narrowband emission with full-width at half-maximum of 22–24 nm and high photoluminescence quantum yields of ∼100%. The tri-spiral donor configuration further improves horizontal dipole orientation for the enhanced light outcoupling. As a result, the optimal Ts-NBN-based OLED achieves a maximum external quantum efficiency of 39.1% with the CIE y value of 0.70.

By strategically fusing diboron-based polycyclic aromatic hydrocarbon frameworks with dibenzo[b,d]furan units and introducing fluorine-containing units as terminal substituents, highly efficient narrowband pure green-emitting multiple resonance-thermally activated delayed fluorescence materials can be developed, with precisely controlled emission peaks while maintaining a narrow full width at half maximum.

Abstract

To meet the critical demand for ultra-high-definition (UHD) display technology, luminescent materials must achieve precise peak emission positions and narrow emission bandwidths simultaneously. Herein, we report a new class of narrowband pure green thermally activated delayed fluorescence (TADF) materials, DBNDO-1, DBNDO-2, and DBNDO-3. These compounds are constructed on diborane-embedded polycyclic aromatic hydrocarbon (PAH) skeletons fused with a dibenzo[b,d]furan motif. Through strategic incorporation of three distinct terminal substituents, 3,4,5-trifluorophenyl, 4-(trifluoromethyl)phenyl, and 3,5-bis(trifluoromethyl)phenyl units, we further precisely modulate emission maxima while maintaining narrowband emission characteristics. All of these emitters exhibit bright green luminescence and narrowband emission characteristics, with luminescence peaks ranging from 513 to 518 nm. The full width at half maximum (FWHM) is only 14 to 16 nm in dilute toluene solution. Additionally, the photoluminescence quantum yields (PLQYs) for all of these emitters exceed 95%. The corresponding optimized OLEDs based on DBNDO-1, DBNDO-2, and DBNDO-3 achieved peak external quantum efficiencies (EQE_max) of 33.7%, 32.4%, and 32.0%, respectively. The CIEy coordinates for these OLEDs were 0.74, 0.75, and 0.75, with FWHM values ranging from 18.5 to 19.4 nm. To the best of my knowledge, the EQEs, FWHM, and CIEy values represent some of the most exceptional performance metrics reported in the current literature.

Starting from a new macrocyclic arene, 3,6-dimethoxycalix[3]acridine (3,6-DMO-C[3]A), N,O-alternant belt[3]arene (NOAB[3]A) was conveniently synthesized and successfully utilized to construct multi-color supramolecular thermally activated delayed fluorescence (TADF) materials. Notably, the belt[3]arene was also employed for rapid visual and highly selective detection of 2-cyanopyrazine (2CP) with the detection limit of 1.7 mg L⁻¹.

Abstract

In this work, 3,6-dimethoxycalix[3]acridine (3,6-DMO-C[3]A), as a new macrocyclic arene, was synthesized and then applied to the construction of a new kind of N,O-alternant belt[3]arene (NOAB[3]A) by the conversion approach from macrocycle to belt. NOAB[3]A has a regularly hexagonal structure and electron-rich cavity, and it can be successfully utilized as an electron donor to construct supramolecular thermally activated delayed fluorescence (STADF) materials with multi-color emissions by its complexation with electron acceptors with different electron-deficient abilities. Notably, due to the formation of STADF accompanied by fluorescence enhancement and redshift when NOAB[3]A combines with the cyanide-containing aromatic compounds, the belt[3]arene can also be directly used for highly selective, sensitive, and visual detection of 2-cyanopyrazine (2-CP) vapor at trace level. The limit of detection (LOD) concentration for 2-CP reached 1.7 mg L⁻¹, indicating that NOAB[3]A can serve as an excellent sensing platform for detecting 2-CP. This work not only expands the applications of functionalized belt[n]arenes but also provides an innovative insight into the detection application of the STADF strategy.

An isomerization-directed twisted conformation boosts reverse intersystem crossing (RISC), enabling a fast RISC rate of 7.1 × 10⁵ s⁻¹, narrowband blue emission, and strong resistance to aggregation. The resulting devices deliver an external quantum efficiency (EQE) of 32.7% with suppressed roll-off at high luminance.

Abstract

The organic light-emitting diode (OLED) performance of multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters is fundamentally constrained by their slow reverse intersystem crossing (RISC) and pronounced aggregation-caused quenching (ACQ). Herein, through regioselective borylation, we design and synthesize a series of blue MR-TADF emitters. The regioisomerization-directed twist configuration synergistically enhances RISC while suppressing ACQ, without compromising spectral purity. The emitter with twist configuration exhibits a remarkably fast RISC rate constant (k _RISC) of 7.1 × 10⁵ s⁻¹, narrowband blue emission with a small full-width at half maxima (FWHM) of 23 nm, and a high photoluminescence quantum yield of 94%. The corresponding OLEDs deliver high-performance narrowband blue emission, with a maximum external quantum efficiency (EQE_max) of 32.4%, and alleviated efficiency roll-off at high luminance (EQE₁₀₀₀ = 22.2%). Notably, excellent performance is retained even at elevated doping levels (EQE_max = 29.4% at 20 wt%). This work provides a design paradigm for advancing blue MR-TADF emitters toward practical display technologies.

Based on symmetry breaking strategy, two tailored TADF materials with ultrafast reverse intersystem crossing and high photoluminescence quantum yields are developed, which can function efficiently as emitters in nondoped OLEDs and sensitizers in hyperfluorescence OLEDs, and provide outstanding external quantum efficiencies of up to 31.2% and 40.2%, respectively.

Abstract

Reverse intersystem crossing (RISC) process is critical for thermally activated delayed fluorescence (TADF) materials to realize spin–flip of triplet excitons in organic light-emitting diodes (OLEDs), but the RISC processes of most TADF materials are not fast enough, undermining electroluminescence (EL) efficiency stability and operational lifetime. Herein, a symmetry breaking strategy to accelerate RISC processes is proposed. By designing asymmetric electron-withdrawing backbone consisting of benzonitrile and xanthone/thioxanthone groups, two new asymmetric TADF molecules, 4tCzCN-pXT and 4tCzCN-pTXT, with multiple 3,6-di-tert-butylcarbazole donors are successfully developed. They own increased molecular vibrations, which promote intrinsic RISC process and enable multi-channel transitions via vibronic coupling of high-lying triplet states. Consequently, they exhibit fast RISC rates of up to 1.24 × 10⁷ s⁻¹, being one order of magnitude higher than that of the symmetric control molecule. They can perform as luminescent materials in OLEDs, providing outstanding external quantum efficiencies (EQEs) of up to 31.2% and 35.8% in non-doped and doped devices, respectively, with very small roll-offs. The OLEDs using them as sensitizers for multi-resonance emitters achieve remarkable EQEs over 40%, and extraordinary operational stability with LT ₉₀ of 24974 h at 1000 cd m⁻², demonstrating their great potentials in OLEDs.

A novel electron injection method is demonstrated for organic light-emitting diodes (OLEDs) using magnesium/silver (Mg/Ag) electrode. By controlling the penetration of Mg atoms into the electron transport layer (ETL), electrons can be efficiently injected through conducting defect levels within ETL to obtain extremely low turn-on voltage and negligible efficiency roll-off in OLEDs.

Abstract

Efficient carrier injection from electrodes into organic layers is of significance for designing high-performance organic light-emitting diodes (OLEDs), but the high work function of the metal cathode is often unfavorable for electron injection. Herein, a novel electron injection method is demonstrated for OLEDs using magnesium/silver (Mg/Ag) electrode. By controlling the penetration of Mg atoms into the electron transport layer (ETL), electrons can be efficiently injected through conducting defect levels within ETL generated during the Mg deposition process. The undoped device using the typical Tris(8-hydroxyquinolinato)aluminum (Alq₃) emitter, Bathophenanthroline (Bphen) ETL, and Mg/Ag electrode exhibits record-low turn-on voltage of 2.4 V and negligible efficiency roll-off. The doping device using Mg/Ag electrode also shows a low turn-on voltage of 2.7 V, a 2.7-fold enhancement in brightness from 43138 to 116611 cd m^{− 2}, and an amazing suppression in efficiency roll-off from 51.8% to 12.7% compared to those of the device with commonly-used LiF/Al electrode. More importantly, the efficient electron injection still keeps even under low driving voltage (3 V) and low ambient temperature (225 K). This advantage overcomes the critical drawback of OLEDs whose electron injection heavily depends on the applied electric field and operational temperature, thus promising for developing top-class widely-used devices.