Organic full-color narrowband afterglow†

Yincai Xu‡ ^a, Yufeng Xue‡^a, Le Mei^b, Zongliang Xie^a, Zhu Wu^a, Zheng Yin^a, Xian-kai Chen*^b, Yue Wang^c and Bin Liu*^a
aDepartment of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore. E-mail: cheliub@nus.edu.cn
^bInstitute of Functional Nano and Soft Materials (FUNSOM), Soochow University, Suzhou 215123, P. R. China. E-mail: xkchen@suda.edu.cn
^cState Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012, P. R. China

First published on 11th July 2025

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New concepts A facile, feasible and general host–guest doping strategy is developed to achieve organic full-color narrowband afterglow (OFNA). The obtained OFNA spans from 468 to 669 nm, with full-width at half-maximum values of ≤0.21 eV and Commission Internationale de L’Eclairage coordinates ranging from (0.142, 0.190) to (0.733, 0.267). This is the first study to achieve afterglow by stabilizing the triplet excitons of boron–nitrogen-containing MR-TADF materials.

1. Introduction

With the rise of the Internet of Things and smart devices, ultra-high-definition display technology has been widely adopted, enhancing image resolution and providing a more delicate and lifelike visual experience.¹ It has emerged as a key research area and strategic priority within the display community, posing a huge challenge to the color purity of luminescent materials.² Organic afterglow is the phenomenon that organic materials continue to emit light for a period after the excitation source is removed.³ With advantages such as low production cost, easy construction, and tunable optoelectronic properties, it has broad applications such as afterglow display, data encryption and information storage.⁴ Organic afterglow is generally achieved through strategies such as crystal engineering, host–guest doping, or polymerization to generate organic room temperature phosphorescence (RTP), and long-lived emission from milliseconds to seconds can be visualized.⁵ Alternatively, it can be achieved through the use of two-photon ionization systems⁶ or charge-separation–charge-recombination processes to produce organic long persistent luminescence (OLPL)⁷ induced via exciplex emission, and long-lived emission from minutes to hours can be sustained. After decades of efforts, remarkable progress has been made in photoluminescence quantum yield (Φ_PL), lifetime (τ), duration and potential applications related to organic afterglow. However, most reported afterglow emission exhibits a broad full-width at half-maximum (FWHM) (>80 nm) or is accompanied by uneven shoulder peaks, resulting in poor color purity.⁸ This is usually attributed to the strong vibrational coupling between the ground (S₀) state and excited state in RTP materials, as well as the large structural relaxation of the lowest triplet (T₁) state, and the intermolecular charge transfer of the exciplex in the OLPL system.⁹ This inherent luminescence mechanism hinders the development and bandwidth regulation of high-color-purity afterglow emitters, leaving the exploration of organic full-color narrowband afterglow (OFNA) significantly behind.¹⁰

To address these challenges, we focus on purely organic thermally activated delayed fluorescence (TADF) afterglow, as the fluorescence emission mechanism, originating from a single component molecule, is easy to manipulate.¹¹ This simplicity facilitates the construction of molecular architectures with narrowband emission (Scheme 1). The mechanism for accessing TADF afterglow is based on the following principles:¹² (1) stabilizing triplet excitons without undergoing radiative transition and with minimal non-radiative transition losses; this requires the use of a suitable host to create a rigid, compact, dense, and congested microenvironment, thereby restricting the molecular vibrations, rotations, and collisions, which stabilizes vulnerable triplet excitons. (2) slowing down the reverse intersystem crossing (RlSC) process of triplet excitons; this necessitates a modest singlet–triplet energy splitting (ΔE_ST), with 0.10–0.20 eV being the ideal value. A smaller ΔE_ST will accelerate conversion from the triplet to the singlet state, while a larger ΔE_ST will increase the likelihood of triplet exciton quenching. (3) Excitons repopulated in the singlet state should undergo a rapid fluorescence process. This requires TADF emitters with a fast prompt fluorescence rate. Subsequently, the keys to achieving OFNA include (1) constructing an emitter with intrinsic narrowband emission; (2) ensuring high chemical tunability of emitters to facilitate easy access to the full-color electromagnetic spectrum. Recently, multiple resonance TADF (MR-TADF) materials tailored for ultra-high-definition organic electroluminescence displays have established a well-defined paradigm for high-color-purity emitters.¹³ Typically, MR-TADF molecules are composed of para-arranged donor and acceptor atoms/groups embedded within polycyclic aromatic hydrocarbons. The complementary resonance effects between donors and acceptors – reminiscent of the charge delocalization resonance of zwitterions around a six-membered ring – induce the frontier molecular orbitals (FMOs) to alternate across atoms/groups of the entire conjugated skeleton, leading to molecular Franck–Condon transition processes characterized by short-range charge transfer, akin to localized excitation.¹⁴ This alternating distribution pattern minimizes the overlap of FMOs, diminishes ΔE_ST, and promotes TADF behavior. Uniquely, this mechanism suppresses the stretching vibration between atoms and reduces the vibrational coupling between S₀ and the lowest singlet (S₁) state. Therefore, MR-TADF molecular entities usually possess a small Stokes shift and a narrow FWHM. Generally, boron–nitrogen-containing MR-TADF emitters have very narrow FWHMs and near-unity Φ_PLs in the MR molecule library,¹⁵ and their highly tunable chemical structures can easily cover the full-color electromagnetic spectrum, making them excellent candidates for OFNA.

In this contribution, we screened a set of panchromatic boron–nitrogen-containing MR-TADF emitters, which were mixed with a host matrix, tris(2-methylphenyl)phosphine oxide (TTPO), followed by melting–cooling into a glassy state and subsequent photoactivation to achieve OFNA. Molecular dynamics simulations indicate that the glassy morphology formed by heating–annealing of TTPO can offer an intricate rigid microenvironment for MR-TADF emitters, which can effectively restrict the molecular vibrations and stabilize their conformations. Upon photoactivation of the mixed films, the triplet excitons slowly return to the singlet state, emitting afterglow. The achieved OFNA wavelengths vary from 468 to 669 nm, with FWHMs ≤ 0.21 eV and Commission Internationale de L’Eclairage (CIE) coordinates ranging from (0.142, 0.190) to (0.733, 0.267). The Φ_PLs of these films range from 50 to 80%, and representative MR emitters are adopted to construct high-color-purity flexible organic afterglow fibers and optical waveguide fibers. In addition, the afterglow lifetimes are in the range of 0.03–0.3 s, based on which the data encryption application is developed. This study provides a facile, feasible and general host–guest doping strategy to achieve organic full-color narrowband afterglow. This is the first study to achieve afterglow by stabilizing the triplet excitons of boron–nitrogen-containing MR emitters, which has enabled an important reconstruction of the excited states of contemporary boron–nitrogen-containing MR-TADF materials and afforded a method to systematically regulate the excited states.

2. Results and discussion

2.1. Materials design and film fabrication

For the host material, a commercially available rigid matrix, TTPO, was selected, which can be synthesized from the very cheap precursor tri(2-methylphenyl)phosphine via one-step hydrogen peroxide oxidation (Scheme S1 and Fig. S1, ESI†). TTPO is an organic small molecular glass that can form a viscous supercooled liquid between the glass transition temperature and melting point, and then can form an amorphous solid when rapidly cooled to ambient temperature.¹⁶ The presence of three methyl groups in the molecule disrupts the symmetry of three phenyl groups, resulting in an irregular structure and various conformations, slowing down the crystallization rate and generating an amorphous solid state at room temperature.¹⁷ It is anticipated that TTPO can be used as a glassy host material with good processability, providing a stiff, compact, dense, and congested microenvironment, thereby immensely suppressing the molecular vibrations, rotations, and intermolecular collisions of guest molecules. This helps to stabilize the triplet excited state conformation that is susceptible to the external environment. In addition, the high triplet energy level of TTPO (E_T1 = 2.95 eV) can avoid energy reverse transfer from the guest molecules after being excited in the host–guest doping system (Fig. S2, ESI†). To achieve OFNA, nine representative boron–nitrogen-containing MR-TADF materials were carefully selected, namely: tCzBNO, DtDPABN,¹⁸ DtCzBN,¹⁹ m-3CzBN, m-3tCzBN,²⁰ DtCzBN-Bpin,²¹ BN-Cb,²² BNO2,²³ and R-BN.²⁴ The diverse samples ensure a gradient of emission in toluene, enabling fine control from blue to red. Among them, tCzBNO and m-3CzBN are newly designed and synthesized (Schemes S2, S3, Fig. S3–S8 and Table S1, ESI†), and the other seven molecules have already been reported. These nine compounds exhibit vivid fluorescence under 365 nm ultraviolet (UV) light irradiation in toluene solution (1 × 10⁻⁵ M, 298 K), covering the panchromatic electromagnetic spectrum. The emission peaks are located at 457–662 nm, with corresponding FWHMs of 22–41 nm/0.11–0.19 eV, ΔE_STs of 0.08–0.25 eV, and absolute Φ_PLs of 83–100% (Fig. S9–S17 and Table S2, ESI†). Given that TTPO is an excellent glassy host material and the selected MR-TADF emitters have the desired unique luminescent behaviors, it is anticipated that the integration of the host matrix TTPO and MR-TADF emitters will enable the achievement of desired OFNA.

To harvest OFNA, under ambient atmosphere, various MR-TADF emitters with 0.5 wt% doping concentration were first mixed with TTPO on a glass substrate, heated and melted at approximately 160 °C, and then rapidly cooled to room temperature to fabricate a glassy doped thin film. Then, the thin films were activated using a 100 W 365 nm UV flashlight for about 30 seconds to 1 minute. After removing the light source, an appreciable afterglow phenomenon can be observed. The afterglow spectra were tested and analyzed and found to be consistent with the steady-state fluorescence spectra of the as-prepared films.

2.2. Photophysical properties and mechanism of narrowband afterglow from the representative MR-TADF emitter DtCzBN in the host TTPO

First, we selected the sky-blue-light-emitting star MR molecule DtCzBN (λ_PL = 481 nm, FWHM = 22 nm), a classic parent molecular structure widely used in organic electroluminescent materials,²⁵ as a representative guest emitter, and determine the optimal doping ratio by investigating its spectra, Φ_PLs, and afterglow lifetimes under different doping ratios in the host TTPO. A low doping concentration signifies a small number of luminophores, while an increase in doping concentration means that the quenching behavior between luminescent molecules will become stronger. In addition, there is a significant discrepancy between the molecular structures of DtCzBN and TTPO, and miscibility needs to be considered, as a high doping concentration may unintentionally induce phase separation or crystallization. Therefore, combining the host and guest doping dose used in TADF afterglow or RTP based on conventional host–guest doping systems, we focused on three doping concentrations of 0.1 wt%, 0.5 wt% and 1.0 wt% in this study. The results show that TTPO thin films doped with 0.1 wt%, 0.5 wt% and 1.0 wt% DtCzBN exhibit light-green fluorescence, with corresponding emission maxima of 499, 506 and 508 nm, narrow FWHMs of 31, 33 and 35 nm, and Φ_PLs of 31.9%, 62.9% and 32.3%, respectively (Fig. 1a–c). The intensity of the steady-state spectra and Φ_PLs first increase with the luminophore quantity and then decrease, and the latter is due to aggregation and concentration quenching. However, the FWHMs do not change significantly with the doping concentration of the emitter DtCzBN. After photoactivation, TTPO thin films doped with 0.1 wt%, 0.5 wt% and 1.0 wt% DtCzBN exhibit afterglow maxima of 499, 505 and 508 nm, narrow FWHMs of 32, 33 and 34 nm, respectively, and the total Φ_PLs of the films are 45.0%, 70.9% and 42.3%, respectively (Fig. 1d–f). The afterglow spectral profiles (including peak maxima and FWHMs) are highly consistent with their corresponding steady-state spectra, and no exciplex/excimer emission or phosphorescence emission is observed, which preliminarily confirms that the afterglow originates from TADF (Fig. S18, ESI†). Since the afterglow intensity was greatly weakened compared with that of the corresponding steady-state spectrum, the afterglow spectra were captured using a charge coupled detector spectrometer and the afterglow lifetimes were fitted automatically with an R-square (coefficient of determination, COD) >0.98. As a result, TTPO thin films doped with 0.1 wt%, 0.5 wt% and 1.0 wt% DtCzBN show afterglow decay lifetimes of 0.166, 0.180 and 0.135 s, respectively (Fig. 1g–i), close to each other. Further increasing the doping concentration of DtCzBN in TTPO films to 2 wt% and 3 wt% led to further decreased afterglow (Fig. S19, ESI†). Therefore, taking into account the steady-state spectral intensity/Φ_PL, FWHM, and afterglow decay lifetime, the optimal DtCzBN doping concentration was ultimately determined to be 0.5 wt%.

Subsequently, to gain a deeper understanding of the luminescence characteristics of DtCzBN doped in TTPO, the intrinsic lifetime of the TTPO thin film doped with 0.5 wt% DtCzBN before photoactivation was measured. The transient photoluminescence decay curve of the doped thin film TTPO:0.5 wt% DtCzBN shows bi-exponential decays, with 89% nanosecond-scale prompt fluorescence (τ = 13.4 ns) and 11% microsecond-scale delayed fluorescence (τ = 91.1 μs) at room temperature under vacuum conditions (Fig. S20a, ESI†), which is a typical indicator of TADF behavior. In addition, as the temperature is elevated from 80 to 320 K (interval: 40 K), the delayed fluorescence components of recursive S₁ → S₀ transitions through successive upconversion of triplet excitons are gradually strengthened (Fig. S20b, ESI†), which further substantiates the TADF characteristics of the emitter DtCzBN in the host TTPO.

2.3. Molecular dynamics simulations and noncovalent interactions of the doped thin film TTPO:0.5 wt% DtCzBN

To investigate the molecular arrangement in the doped thin film TTPO:0.5 wt% DtCzBN, all-atom molecular dynamics (AA-MD) simulations were conducted for visualization.²⁶ The simulation findings reveal that the guest molecules DtCzBN are dispersed throughout the host matrix rather than clustering together, which is attributed to their low concentration. Thermal equilibrium configuration analysis demonstrates that isolated DtCzBN clusters are tightly encapsulated by TTPO molecules (Fig. 2a and b). By utilizing the radial distribution function (RDF),²⁷ denoted as g(r), we can quantify the probability of finding a particle at a specific distance from a reference particle, thereby verifying the packing arrangement within the thin film. The prominent first peak at 9 Å in the g(r) plot between boron atoms of DtCzBN molecules and oxygen atoms of TTPO molecules suggests a strong tendency for these atoms to interact (Fig. 2c), facilitated by the exposed oxygen atoms in TTPO molecules. To pinpoint the primary interactions driving the molecular packing, symmetric-adapted perturbation theory (SAPT) energy decomposition calculations²⁸ were performed on individual pairs extracted directly from the MD-simulated film. These calculations indicate that variations in packing configurations result in different levels of intermolecular interactions, including electrostatic interactions (−9.22 kJ mol⁻¹), exchange interactions (23.68 kJ mol⁻¹), induction forces (−2.93 kJ mol⁻¹) and dispersion forces (−33.27 kJ mol⁻¹). Notably, the dispersion interaction was found to be the strongest and to dominate the final binding energies (−21.74 kJ mol⁻¹) (Fig. 2d). Its energy is comparable to that of a strong hydrogen bond (∼40 kJ mol⁻¹), suggesting a strong and tight stacking between TTPO molecules.

To gain more insight into the noncovalent interactions (NCIs) within the doped thin film TTPO:0.5 wt% DtCzBN, we conducted an independent gradient model based on the Hirshfeld partition of molecular density (IGMH)²⁹ and Hirshfeld surface analysis³⁰ using the simulated structure. Fig. 3a presents a visual representation of the three-dimensional interaction landscape through isosurfaces colored IGMH isosurface maps (Top left) based on the optimized geometry according to the sign(λ₂)ρ parameter (isovalue = 0.05 a.u.), highlighting the regions where the spatial NCIs between the guest and host molecules predominantly occur.

The observed extended planar green isosurfaces between DtCzBN and TTPO molecules indicate that the electron density in the corresponding weak van der Waals interactions is very low, close to zero, and can be attributed to the dispersion effect, which is an intermolecular attraction that can lower the energy of the entire system. To further analyze the intermolecular interactions within the molecular clusters, we utilized Hirshfeld surface analysis to visualize the interactions in the molecular packing mode. As shown in Fig. 3b, the small area of red isosurface portions, indicative of intermolecular contacts, is primarily distributed between the phenyl group and hydrogen atoms. This region is mainly composed of C⋯H interactions, corresponding to the light-yellow patches on the fingerprint plot of the Hirshfeld surface. In the three-dimensional Hirshfeld surface, the dispersion interaction is the predominant interaction, which is also evident in the decomposed fingerprint plot. Specifically, the involvement of stacking arrangements appears as a large area of deep purple-blue regions or nearly white spots near the center of the plot. Therefore, combining the results of IGMH and Hirshfeld surface analysis, the dispersion interaction is dominant between the guest DtCzBN and the host TTPO in the doped thin film TTPO:0.5 wt% DtCzBN. In summary, molecular dynamics simulations demonstrate that the TTPO matrix can provide a sophisticated rigid microenvironment for DtCzBN molecules, which can effectively lock the molecular vibrations and stabilize its conformation.

2.4. Organic full-color narrowband afterglow

To verify the simplicity, feasibility and universality of the host–guest doping strategy based on the host TTPO to construct organic full-color narrowband afterglow, more congener MR-TADF molecules of DtCzBN were examined. For intuitive comparison, nine research objects, tCzBNO, DtDPABN, DtCzBN, m-3CzBN, m-3tCzBN, DtCzBN-Bpin, BN-Cb, BNO2 and R-BN, were sequentially doped in TTPO with 0.5 wt% doping concentration and nine films were fabricated according to standard operating procedures. The results indicate that the maximum wavelengths of OFNA derived from these emitters correspond to 468, 477, 505, 521, 533, 522, 572, 626 and 669 nm, with FWHMs of 38/0.21, 34/0.18, 33/0.16, 47/0.21, 42/0.18, 42/0.18, 54/0.20, 60/0.19 and 48/0.14 nm/eV, and CIE coordinates of (0.142, 0.190), (0.180, 0.328), (0.221, 0.606), (0.263, 0.610), (0.299, 0.621), (0.266, 0.684), (0.511, 0.483), (0.684, 0.315) and (0.733, 0.267), respectively (Fig. 4 and Table 1, Fig. S21, S22, ESI†). The CIE coordinates of the afterglow from emitters tCzBNO, DtCzBN-Bpin, and BNO2 approach the standard three primary colors’ (red, green, blue) light CIE coordinates of (0.14, 0.08), (0.21, 0.71) and (0.67, 0.33) specified by the National Television Standards Committee (NTSC) from the United States and Japan. These three points cover most of the range of tongue-shaped CIE color coordinates and demonstrate the potential to achieve wide color gamut display. In addition, the total Φ_PLs of these films under ambient atmosphere are 77.65%, 56.6%, 70.9%, 58.0%, 56.7%, 64.6%, 52.9%, 51.2% and 57.5%, respectively. The afterglow spectral profiles (including the spectral profile, emission peak and FWHM) of these nine classic MR-TADF emitters are highly consistent with their corresponding steady-state fluorescence spectra, directly proving that the afterglow comes from delayed fluorescence, which can only originate from the RISC process of the triplet state to the singlet state and then radiative transitions. In addition, these profiles are distinct from the phosphorescence emission of emitters and do not show any exciplex/excimer formation, further validating that the afterglow originates from TADF (Fig. S23–S30, ESI†).

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It is worth noting that the absorption of the TTPO molecule in a dilute solution of dichloromethane is mainly in the range of 250–280 nm, and the emission is mainly in the range of 280–350 nm, while the absorption of the pure TTPO film extends to 280–400 nm, and the emission extends to 350–400 nm (Fig. S31, ESI†). The large red-shift of absorption and emission in films relative to that in solution indicates that TTPO in the aggregated state has dense interactions. The steady-state spectra of all doped films are measured after 365 nm UV light excitation, while the pure TTPO film has very weak absorption near 365–400 nm and very weak emission near 365–450 nm, which means that TTPO molecules in the doped film are also partially excited. In addition, the triplet energy level of TTPO is higher than the singlet and triplet energy levels of all MR emitters (Fig. S32, ESI†), and the HOMO and LUMO energy levels of TTPO include the HOMO and LUMO energy levels of all MR emitters (Fig. S33, ESI†), so an energy transfer channel could be generated. Therefore, there are two possible pathways for the energy source of the terminal steady-state fluorescence emission of the entire films, namely, direct excitation of MR emitters and energy transfer after excitation of the host TTPO (Fig. S34, ESI†). Since residual oxygen is inevitably present in the system when glass films are prepared under ambient conditions, the afterglow is inactive and cannot be observed by the naked eye without photoactivation. After continuous irradiation for 30 seconds to 1 minute, clear and bright afterglow can be observed in the amorphous MR emitter doped TTPO films. This phenomenon can be attributed to the gradual consumption of residual ground-state oxygen by triplet excitons generated by guest MR emitters.³¹ In addition, combined with the molecular dynamics simulation results, overall, in the entire blended film, the host TTPO plays an important role in dispersing, immobilizing, confining and stabilizing MR-TADF emitters. All afterglow is fluorescence emission only, which is harvested by the energy stored in the stable triplet state recovering to the singlet state through a slow RISC process and then radiating after the excitation light source is removed. Finally, the afterglow decay lifetimes of the nine films are tested sequentially, which are 0.210, 0.260, 0.180, 0.140, 0.141, 0.298, 0.123, 0.153 and 0.037 s, respectively (Fig. S35–S42, ESI†). It can be concluded that fixing the molecular conformations of MR-TADF emitters through the host TTPO, their excited state lifetimes can be effectively regulated. Taking the emitter DtCzBN as an example, its delayed fluorescence lifetime in conventional rigid all-carbazole derivatives is about 40–100 μs,³² while the afterglow lifetime in TTPO can reach 0.180 s. Therefore, this study also provides an inspiring solution for extending the excited state lifetime. The various sample emitters and results presented above demonstrate that this study introduces a facile, effective and general host–guest doping strategy to achieve organic full-color narrowband afterglow.

2.5. Flexible organic afterglow fibers, optical waveguide fibers, and data encryption

By utilizing the excellent processability of MR emitters and TTPO, high-color-purity flexible organic afterglow fibers, optical waveguide fibers, and data encryption devices can be developed. For example, by simply thermal-drawing a supercooled liquid of a TTPO:0.5 wt% BNO2 mixture, a high-color-purity red afterglow glass fiber with a knotted helical structure was prepared, exhibiting bright and vivid afterglow emission under 365 nm UV light and after the removal of UV light (Fig. 5a). Furthermore, leveraging the good miscibility of BNO2 and DtCzBN-Bpin with TTPO, high-color-purity optical waveguide fibers were fabricated. Fluorescence can propagate along the optical fiber, and self-optical waveguide can occur when the optical fiber focus is excited (Fig. 5b). Flexible optical fibers have the potential to be employed as a one-dimensional optical waveguide microrod for photon-based information delivery.³³ The narrowband emission properties are conducive to selectively filtering unnecessary wavelengths of light on demand, reducing interference, improving the quality and stability of data transmission, as well as signal quality and contrast, and increasing energy utilization efficiency.³⁴ Finally, due to the decent afterglow lifetime and high color purity of DtCzBN-Bpin in TTPO, it was chosen as a model sample for data encryption applications (Fig. 5c). A homogeneous glassy solid was prepared by mixing TTPO:0.5 wt% DtCzBN-Bpin and PMMA (poly(methyl methacrylate)):0.5 wt% DtCzBN-Bpin in a 36-well plate on a quartz substrate. The former mixture was filled into wells forming the letters “LIU”, while the latter was added to the remaining wells. Under 365 nm UV irradiation, the entire plate displays bright green emission, making it difficult to decipher the encoded information. When the UV light is turned off, the entire plate appears completely black without any visible information. As the entire 36-well plate is photoactivated, subsequently irradiated with 365 nm UV light and turned off, the letters “LIU” become very clear and easily distinguishable. This dual encryption approach enables a more secure data encryption strategy, while the high-color-purity afterglow display significantly enhances image resolution and clarity, which is beneficial for maintaining data accuracy and retrievability in data encryption applications, representing a meaningful step towards the development of high-color-purity information anti-counterfeiting technology.

3. Conclusions

In conclusion, we have proposed a simple and general host–guest doping strategy to achieve organic full-color narrowband afterglow. The obtained OFNA spans from 468 to 669 nm, with FWHMs of ≤0.21 eV and CIE coordinates ranging from (0.142, 0.190) to (0.733, 0.267). Molecular dynamics simulations demonstrate that the glassy morphology formed by TTPO after heating–annealing can provide a rigid microenvironment for fluorophores, thereby effectively restricting the molecular vibrations and stabilizing their conformations. After the blended films are photoactivated, the triplet excitons slowly return to the singlet state, releasing afterglow. Finally, representative MR emitters are employed to develop high-color-purity flexible organic afterglow fibers, optical waveguide fibers, and data encryption applications. This research endeavor represents a progress in the development of high-efficiency, full-color, narrowband afterglow materials, overcoming the inherent challenges in improving the color purity of organic afterglow. In addition, this study provides a systematic approach to modulate the excited states of MR-TADF emitters, offering a strategy to extend their lifetimes and paving the way for future high-color-purity afterglow displays.

Author contributions

L. Mei performed the theoretical calculations. Z. Xie, Z. Wu, and Z. Yin participated in data analyses. Y. Xu, L. Mei, X.-K. Chen and B. Liu wrote the manuscript. Y. Wang provided suggestions for the manuscript.

Conflicts of interest

There are no conflicts to declare.

Data availability

The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request. The data include experimental results, characterization data, and any computational models used in the analysis. The following specific data types are available: raw and processed data – experimental measurements, including raw data from spectroscopic, NMR, and other characterization techniques. Requests for data should be directed to cheliub@nus.edu.sg. The data will be made available in a timely manner to ensure transparency and reproducibility of the results presented in this study.

Acknowledgements

This study was supported by the Singapore National Research Foundation Investigatorship (A-8002259-00-00, B. L.) and the Tan Chin Tuan Centennial Professorship (E-467-00-0012-02). Prof. X.-K. Chen acknowledges the financial support from the National Natural Science Foundation of China (Grant No. 52473190), the Natural Science Foundation of Jiangsu Province (Grant No. BK20240042), and the Science and Technology Project of Suzhou (Grant No. ZXL2024394). The authors gratefully thank Prof. Yang Zou and Prof. Chuluo Yang (Shenzhen University) for providing BNO2, and Dr Ji-Kun Li and Prof. Xiao-Ye Wang (Nankai University) for providing R-BN.

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Footnotes

† Electronic supplementary information (ESI) available: Compound syntheses and characterization, and other spectra. Additional information such as detailed experimental procedures, intermediate data, and supplementary figures. CCDC 2403790. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d5mh00980d

‡ Y. Xu and Y. Xue conceived the experiments and contributed equally to this work.

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