English

• Organic persistent luminescence, or afterglow emitters, are widely utilized in applications such as light sources, biological imaging, sensing, information security, and light-emitting devices, garnering significant interest from researchers [1-6]. Substantial advancements have been achieved in organic persistent emitters characterized by high quantum yield and extended emission lifetimes, which are also readily processable and synthesizable [7,8]. According to the Kasha rule, photons are typically emitted from the lowest excited state of a molecule, which results in most organic persistent emitters exhibiting a single emission band [9]. The decay from triplet and singlet excited states, respectively, is vital for materials to exhibit both RTP and TADF [10,11]. However, the competition between reverse intersystem crossing (RISC) and direct radiative emission of triplet excitons presents a substantial challenge in molecular design aimed at regulating dual emission (Scheme S1a in Supporting information) [12]. Notably, compared to UV light, visible and near-infrared light serve as safer excitation sources [13]. However, achieving broad-spectrum dual emission from both TADF and RTP, excited by both UV and visible light, remains a challenge, particularly the up-converted afterglow emission stimulated by near-infrared light in single-component systems. Broad-spectrum excitation and emission are essential for the widespread application of these materials. Although RTP excited by visible light has been documented, crimson afterglows with maximum RTP peaks above 600 nm remain scarce [14]. In particular, organic materials not only have flexible designability and better biocompatibility, but also can be excited by visible light with ultra-long afterglow as well as near-infrared light source excitation upconversion afterglow material luminescence properties, so that it has potential applications in bioimaging.

  For most organic afterglow materials, crystallization is the most prevalent strategy to obstruct oxygen quenchers, facilitate small molecule curing, and effectively minimize the non-radiative decay of triplet states [15]. However, the practical application and development of afterglow materials face significant limitations due to mechanical grinding or melting that can destroy the crystal structure, among other factors [16]. Indeed, developing afterglow emissions that are not confined to crystalline states or other challenging environments remains a substantial challenge [17]. Organic luminescent materials exhibit stimulus responsiveness due to changes in molecular conformation in the ground or excited state, alterations in molecular packing mode, or photochemical reactions between molecules [18]. Consequently, under external stimuli such as mechanical force, temperature, light, pH, and organic vapor, these materials can undergo changes in the molecular environment that easily quench the triplet state, leading to the cessation of afterglow emission. Reports of single-component, multi-level stimulus-responsive luminescent materials based on afterglow changes are rare. Nitrogen-containing heterocyclic polycyclic aromatic hydrocarbons with large π-conjugation planes may form highly stable dimers. These interactions liberate the materials from the constraints of crystallization, making them ideal candidates for achieving high-performance afterglow emission in the amorphous state [19].

  In addition to crystallization limitations, ultra-long afterglow materials functional in aqueous or strong acid-base environments are gaining widespread attention due to their significant potential in biological imaging and water-based encryption inks [20]. Typically, achieving stable TADF and RTP emissions in water is challenging, primarily because of the disruption of strong intermolecular interactions, such as hydrogen bonds, or the quenching of dense triplet excitons by external quenchers like dissolved oxygen [21]. Researchers have implemented effective strategies including the formation of organic nanoparticles, macrocyclic supramolecular assembly, in situ encapsulation within hydrogen-bonded organic frameworks (HOFs), and the integration of phosphorescent molecules with supramolecular scaffolds to stabilize afterglow emission in aqueous environments [22-25]. Despite these advancements, developing stable emission properties for single-component afterglow emitters in the aqueous phase remains challenging and less explored.

  In this study, we designed triplet excitons based on monomolecular 6,12-diphenyl-5,6,11,12-tetrahydroindolo[3,2-b]carbazole (CZID) and its derivatives (Scheme S1b in Supporting information) to enable solid-state, dual-persistent TADF and RTP emission. The luminescent core was centered on 5,6,11,12-tetrahydroindolo[3,2-b]carbazole. Experimental results demonstrated that the RTP lifetime of these compounds could be successfully extended from 4.19 ms to 399.70 ms under visible light excitation through tuning the superposition between substituents and associated molecules. Additionally, the afterglow emission could be easily and continuously tuned from yellow to red within a 100 nm range. Moreover, the ultra-wide absorption range of 200–800 nm allows these afterglow materials to be readily excited by sunlight simulator or near-infrared light, with the yellow-to-red upconversion RTP lifetime under 808 nm excitation reaching approximately 13.72 µs. Notably, the emission characteristics of CZID derivatives are intimately associated with molecular conformation; post-grinding or heat treatment, accompanied by extensive afterglow color conversion. Additionally, the double persistent emission of these compounds varies with temperature, suggesting potential applications in visual temperature detection and anti-counterfeiting. Importantly, these compounds also exhibit stable afterglow emission in aqueous media and strong acid-base environments. In conclusion, we developed a series of single-component smart afterglow materials that can stably emit afterglow in water and strong acid or alkali environments, which provides enlightenment for the wide application of multilevel stimulus-responsive smart materials.

  Compounds CZID, CZID-OH, CZID-CH₃, CZID-1-OMe, and CZID-3-OMe were synthesized by condensing indole with corresponding aromatic aldehydes, as described in protocol (Scheme S2 in Supporting information). Their molecular structures were fully characterized by nuclear magnetic resonance (NMR) analysis, high performance liquid chromatography (HPLC) and high-resolution mass spectrometer (HRMS) (Figs. S36-S55 in Supporting information). Single crystals of these compounds were grown using a solvothermal method, and their photophysical properties in the crystalline state, including emission wavelength, lifetime, quantum yield, and afterglow duration, were studied comprehensively. When excited by an ultraviolet light source, these crystals emit blue radiation, displaying slight variations in the prompt photoluminescence spectrum with emission peaks ranging from 400 nm to 550 nm (Fig. 1a). The fluorescence lifetimes (τ_F) varied between 4.97 ns and 6.26 ns, exhibiting typical fluorescence characteristics (Figs. S1a-S5a and Table S1 in Supporting information). Remarkably, the ultra-long DF and RTP of the CZID series can also be excited under visible light (380–460 nm) as demonstrated in Fig. 1a. Upon cessation of visible light excitation, the delayed emission spectra of the CZID derivatives showed substantial changes after substituent modification, displaying two distinct bands: one overlapping with the fluorescence emission centered at approximately 450 nm, attributed to DF; the other spanning 500–750 nm, corresponding to RTP. Intriguingly, after tuning the substituents, the RTP lifetime of these compounds was extended from 4.19 ms to 399.70 ms (Figs. S1b-S5b, Table S1 in Supporting information), this modification resulted in a variety of afterglow emission colors. The persistent luminescence quantum yield in the crystalline state varied significantly, ranging from 6.5% to 9.2% (Table S2 in Supporting information). Notably, through a simple end-group tuning strategy, the organic phosphor CZID derivatives not only exhibited yellow to red RTP across a broad wavelength range but also ultra-long blue DFs. Such ultra-long, dual-mode persistent luminescence in organic materials has seldom been reported, as most RTP materials typically exhibit only a single long-lived phosphorescent emission [26,27]. The series of compounds demonstrated ultra-long polychromatic afterglow emission, aligning closely with the Commission Internationale de l'Éclairage (CIE) coordinates of the delayed spectrum (Fig. 1b). The introduction of different substituents significantly impacted the afterglow properties of the compounds.

  Figure 1

  

  Figure 1.  Fundamentally photophysical properties of CZID and derivatives. (a) Prompt and Delayed photoluminescence spectra of CZID and derivatives (Delay: 1 ms). (b) The CIE 1931 coordinates of delayed photoluminescence spectra for CZID and its derivatives at 410 nm excitation. (c) Delayed photoluminescence spectra of CZID-CH₃ under 254 nm and 808 nm excitation. (d) Photographs of the compounds CZID, CZID-OH, CZID-CH₃, CZID-1-OMe and CZID-3-OMe in crystalline states under white-light irradiation and at different time intervals after the removal of white-light.

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  Given the ultra-broad delayed excitation spectra range of the CZID series derivatives (Fig. S6 in Supporting information), we also investigated the effect of excitation wavelength on the emission properties of CZID derivatives. As illustrated in Fig. 1c, Figs. S7 and S8 (Supporting information), when the excitation wavelength is shifted to the near-infrared region (808 nm), the delayed emission spectra of CZID series derivatives exhibit similar dual emission bands, significant changes in luminescence lifetime are observed (Figs. S1c-S5c and Table S3 in Supporting information). Consequently, as the excitation wavelength varies, CZID series derivatives are capable of achieving up-converted DF and RTP dual emission. Notably, the compounds we have synthesized can achieve broad-range excitations from ultraviolet, visible, to near-infrared sources, displaying ultra-long multicolor room-temperature afterglow emissions. To our knowledge, there are limited reports of one-component organic molecules that can be excited across a full spectral range to achieve afterglow emissions [28]. As shown in Fig. 1d, upon turning off the white light excitation source, CZID-1-OMe displayed the longest yellow afterglow emission of approximately 11 s, while CZID-CH₃ exhibited an ultra-long red afterglow emission of about 8 s, a relative rarity among organic room temperature phosphorescence emitting materials. As demonstrated in Fig. S9 (Supporting information), upon discontinuing the ultraviolet excitation light, the series of compounds exhibit visible afterglow exceeding 13 s. Furthermore, even when other safer light sources, such as sunlight simulators, are employed in a dark environment, various afterglows lasting several seconds are visible to the naked eye. This may be attributed to their ultraviolet-visible absorption, which extends over an exceptionally broad range.

  In order to elucidate the source of the multi-color long-lived afterglow emission of CZID derivatives, we measured the prompt fluorescence emission spectra, UV–vis absorption spectra and delayed photoluminescence spectra of these derivatives in DMF solution (Figs. S10 and S11 in Supporting information). Notably, strong delayed fluorescence (DF) emission and weak RTP emission were evident in concentrated solutions, differing from their luminescence behavior in the solid state. This variation suggests that afterglow behaviors are influenced not only by the electronic properties of individual molecules but also by the arrangement patterns of molecules within different environments. The single crystal structures of these derivatives were analyzed to further investigate the impact of terminal groups on their luminescence behavior (Figs. S12-S15 and Tables S4-S6 in Supporting information). The CZID series derivatives exhibit both interlinked stacking and parallel face-to-face arrangements in the crystal structure. Analyses first focused on molecular conformations, particularly the dihedral angles formed between the benzene rings and the central framework to evaluate molecular flatness. Our findings revealed that the CZID series compounds exhibit highly twisted molecular configurations, with significant dihedral angles or even near-vertical orientations between the benzene rings and the central skeleton (Fig. S12 in Supporting information). When no terminal group is introduced, CZID show the smallest dihedral angles (59.728° and 58.640°), generally suggesting a larger coplanar structure, whereas a twisted configuration in conjugated systems dampens π-π* and n-π* transitions, potentially suppressing RTP, which may account for the extended afterglow lifetimes observed. Introduction of different electron-donating groups, from methyl to methoxy and then to hydroxyl, results in increasing dihedral angles from 79.031° (CZID-CH3) to 84.952° (CZID-1-OMe) and 86.744° (CZID-3-OMe), and finally to 88.025° (CZID-OH) (Fig. S12 and Table S6 in Supporting information). This indicates that the strength of electron-donating substituents influences the molecular flatness of CZID series derivatives. Additionally, as shown in Figs. S13-S15 and Table S6 (Supporting information), the series compounds exhibit various non-covalent interactions such as C—H…π, π-π, and intermolecular hydrogen bonds, which effectively restrict the intense molecular movement of the CZID series derivatives, thus reducing non-radiative transitions of triplet excitons and resulting in afterglow. Weak π-π interactions may facilitate intermolecular through-space charge transfers (TSCT), accelerating k as well as additional upconversion processes [29].

  In addition, based on the single crystal structure of the CZID series derivatives, we optimized the ground state and excited state structures at the B3LYP/6–31G(d) level using DFT to explore the influence of terminal groups on the luminescence phenomenon (Fig. S16 in Supporting information). Generally, SOC is one of the important factors affecting the phosphorescence lifetime of organic materials. The stronger the SOC, the higher the inter-system crossing (ISC) efficiency of triplet excitons, which shortens the phosphorescence lifetime. This results in the longest afterglow emission lifetime of CZID. Meanwhile, a lower triplet energy level leads to a longer wavelength of phosphorescence emission, through a simple terminal group regulation strategy, SOC and other factors (such as intramolecular charge transfer, molecular packing) work together to make the lifetime and luminescence color of the series of afterglow materials highly tunable.

  Given the outstanding delayed fluorescence (DF) and RTP emission properties of CZID derivatives under visible and near-infrared light excitation, we have conducted a thorough investigation into their temperature-dependent photophysical properties. The emission within the blue spectral region (400–550 nm) displays DF characteristics, characterized by both prompt and delayed components (Table S1). Notably, the delayed fluorescence of CZID exhibits ultralong lifetimes (τ > 100 ms), akin to phosphorescence. According to prior studies, non-radiative deactivation and RISC processes are endothermic and significantly influenced by temperature [30]. As anticipated, at low temperatures, the RTP emission intensity of the derivative crystals in this series increases, while the DF emission intensity decreases (Fig. 2a and Figs. S17a-S20a in Supporting information). Additionally, both photoluminescence and delayed emission colors are temperature-sensitive, with the Commission Internationale de l'Eclairage (CIE) coordinates in Fig. 2b and Figs. S17d-S20d (Supporting information) illustrating the tunability of the delayed emission spectra. Notably, the strong blue DF emission of CZID-CH₃ is suppressed at low temperatures, resulting in a linear shift in the afterglow color. Furthermore, temperature-dependent delayed emission spectra indicate that the DF emission should be attributed to TADF rather than to a triplet-triplet annihilation process.

  Figure 2

  

  Figure 2.  Multilevel stimuli responsiveness of CZID-CH₃. (a) Temperature-dependent delayed photoluminescence spectra and (b) the CIE 1931 coordinates of CZID-CH₃ at crystal state from 273 K to 80 K (λ_ex = 410 nm, delay: 1 ms). (c) The normalized delayed photoluminescence spectra and (d) the CIE 1931 coordinates of CZID-CH₃ in crystalline state and after grinding (λ_ex = 410 nm, delay: 1 ms). (e) The normalized delayed photoluminescence spectra and (f) the CIE 1931 coordinates of CZID-CH₃ in crystalline, after TA and amorphous state (λ_ex = 410 nm, delay: 1 ms). (g) Photographs of CZID-CH₃ after grinding (300 s), TA and amorphous states under white-light irradiation and at different time intervals after the removal of white-light. (h) Prompt and delayed photoluminescence spectra of doped film CZID-CH₃@PMMA (Concentration: 2.5 wt%, λ_ex = 410 nm, delay: 1 ms).

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  Based on the photophysical data of CZID series derivatives, we propose that the first triplet excited state (T₁) of a single molecule is instrumental in facilitating the double persistent emission observed in crystals. Notably, the methoxy group enhances the afterglow emission of CZID derivatives. Taking CZID-1-OMe as a representative case, we employed DFT to optimize the ground and excited state structures at the B3LYP/6–31G(d) level, enhancing our understanding of the luminescence phenomena. As illustrated in Fig. S22 (Supporting information), molecular aggregation leads to a reduced high-energy state (T*) energy level in the dimer compared to the monomer, promoting triplet exciton migration (via triplet-triplet energy transfer) from the monomer to the aggregate [31]. The narrow energy gap between T₁ and S₁ facilitates the RISC process, allowing for persistent TADF and RTP to exhibit emissions from S₁ and T* states, respectively. Time-dependent DFT (TD-DFT) results and the frontier molecular orbitals of CZID-1-OMe are depicted in Figs. S22 and S23 (Supporting information). The analysis reveals that the spin-orbit coupling (SOC) values for S₁-T₂ and S₁-T₃ transitions in both monomers and dimers are higher than those for S₁-T₁ transitions, suggesting additional efficient RISC pathways. These facilitate a swift transition from the intermediate T₂/T₃ state to the S1 state, thereby contributing to rapid k_RISC [32]. Moreover, the SOC value between T* and S_n in the dimer exceeds that in the monomer, indicating an efficient radiative transition of T* in aggregates. As shown in Fig. S24 (Supporting information), the introduction of methoxy groups enhances the CT character of S₁ in monomers, resulting in a blend of strong local excitation (LE) and a weak CT signature, which supports the TADF emission from S₁ in solid-state environments [33].

  The development of achieving both persistent afterglow emission and multi-stage stimulus response is crucial for broadening the application spectrum of these materials. The weak intermolecular forces of the CZID series derivatives may lead to crystal degradation post-grinding or thermal annealing (TA), thereby altering their photophysical properties. As demonstrated in Fig. 2c and Figs. S17b-S20b (Supporting information), the delayed emission spectra of these derivatives vary after different durations of grinding. For CZID, 300 s of grinding does not significantly alter the delayed spectra. In contrast, for CZID-OH, CZID-1-OMe, and CZID-3-OMe, the intensity of the TADF component of the delayed spectra increases progressively with grinding time, while the RTP component remains largely unchanged. This phenomenon may be linked to the weak intermolecular forces within the crystal structures of CZID-OH, CZID-1-OMe, and CZID-3-OMe. Remarkably, as shown in Fig. 2c, CZID-CH₃ exhibits significant changes in its delayed emission spectrum after grinding. Within just 30 s of grinding, the TADF intensity increases, and the RTP emission peak undergoes a partial blueshift. When the grinding extends to 300 s, the RTP emission wavelength experiences a blueshift of approximately 70 nm, highlighting the dynamic changes induced by physical manipulation. The TADF emission intensity of CZID-CH₃ gradually increased and began to dominate over the RTP. The International Commission on Illumination (CIE) coordinates clearly illustrate this color transformation (Fig. 2d).

  To investigate the unique photophysical properties of CZID-CH₃, we analyzed the powder X-ray diffraction (PXRD) patterns of CZID-CH₃ before and after grinding (Fig. S25 in Supporting information). The sharp decrease in diffraction peaks with increased grinding time indicates significant damage to the crystal structure of CZID-CH₃, leading to a transition to an amorphous state. This transition likely contributes to the force-induced stimulation discoloration luminescence observed in CZID-CH₃. Post-thermal annealing (TA) at 80 ℃, changes in the delay spectrum of CZID-CH₃ were more pronounced compared to those observed after grinding (Fig. 2e). Thermogravimetric analysis (TGA) (Fig. S26 in Supporting information) confirmed that the molecular structure of CZID-CH₃ remains intact at TA temperatures, thus excluding luminescence changes due to molecular structural destruction. These experimental findings indicate that CZID-CH₃ transitions from a crystalline to an amorphous state both before and after grinding or TA. Similar trends were observed in other groups of CZID derivatives, both pre- and post-TA, mirroring changes seen after grinding (Figs. S17c-S20c in Supporting information). Their PXRD patterns also reveal a transition from crystalline to amorphous states pre- and post-grinding or TA (Fig. S25). Further studies on the emission properties of the amorphous state of CZID derivatives after melting thermal annealing treatment revealed persistent phosphorescence. As depicted in Fig. 2e and Figs. S17c-S20c, under 410 nm excitation, the delayed emission spectra of the amorphous compounds show similar trends to those observed post-grinding. The International Commission on Illumination (CIE) coordinates clearly illustrate this color transformation (Fig. 2f). The PXRD diffraction peaks in the amorphous state of these compounds are distinct from those in the crystalline state, confirming their amorphous nature (Fig. S25). As shown in Fig. 2g, CZID-CH₃ shifting the afterglow color from red to pink, persisting for over 6.5 s after grinding, while the compounds in the amorphous state exhibit an ultra-long afterglow transitioning from orange to green (Fig. S21 in Supporting information). This demonstrates that our series of CZID derivatives can produce a broad spectrum of long afterglow emissions, ranging from yellow to red, under broad-spectrum excitation in various morphologies.

  To further investigate the luminescence behavior of CZID-CH₃ in its amorphous state, we incorporated CZID-CH₃ into polymethyl methacrylate (PMMA) at a concentration of 2.5 wt%. The X-ray diffraction (XRD) analysis of the doped film, CZID-CH₃@PMMA, confirmed its amorphous properties (Fig. S27 in Supporting information), indicating uniform dispersion of CZID-CH₃ molecules within the polymer matrix. Under UV excitation at 365 nm, the PMMA film displayed dark blue fluorescence but lacked afterglow properties (Fig. S28 in Supporting information). In contrast, the PMMA film doped with 2.5 wt% CZID-CH₃ showed a wide range of delayed excitation properties at 200–450 nm (Fig. S29 in Supporting information), exhibited pink phosphorescent emission after ceasing visible light excitation at 410 nm (Fig. 2h). Interestingly, the prompt fluorescence emission spectra of the CZID@PMMA film and CZID-CH₃ in DMF solution exhibited similar emission peaks, while the delayed emission spectra paralleled the emission trends observed in CZID-CH₃-grinding. Since both the CZID-CH₃-grinding and CZID-CH₃@PMMA samples are approximately amorphous, these findings support the hypothesis that an amorphous state facilitates the planarization of the excited state conformation under photoexcitation. The CZID-CH₃@PMMA film can be easily activated by sunlight simulator since the compound can be excited by a broad spectrum. After irradiation under a sunlight simulator, the pink afterglow emission of the polymer is readily observable in darkness, lasting at least 6 s under ambient conditions (Fig. S30 in Supporting information). Based on these observations, we have developed a novel one-component pure organic intelligent luminescent material capable of afterglow emission and reversible multi-level stimulation response, a rare achievement in the realm of pure organic luminescent materials.

  The solid-state UV–vis absorption spectra of our series of compounds exhibit an ultra-wide range of absorption before and after grinding or thermal annealing (TA), with no significant changes in absorption peaks (Fig. S31 in Supporting information). This stability suggests that the ground state conformations of the compounds remain unaffected. Consequently, we hypothesize that changes in luminescence post-grinding or TA are due to modifications in the excited state conformation. To test this hypothesis, we performed DFT and time-dependent DFT (TD-DFT) calculations using the Gaussian09 program with the B3LYP/6–311G* basis set. Using the single crystal structure of CZID-CH₃ as a basis, we simulated changes in the excited state conformation in response to external stimuli. As shown in Fig. 3, the T₁ energy level in the crystalline state was calculated as 3.605 eV by TD-DFT. Subsequently, we optimized the triplet conformation (T₁) of CZID-CH₃, resulting in a more planar conformation, with a dihedral angle between the benzene ring and the central framework reduced to 63.58°. This finding supports our speculation that, post-grinding or TA, the molecule is likely in a more relaxed environment, causing the excited state conformation of CZID-CH₃ to become more planar, which in turn results in blue-shifted RTP emission. To further verify this, we altered the dihedral angle between the two benzene rings in the excited state conformation to simulate external environmental stimulation. At a dihedral angle of 75.25°, the T₁ energy level of CZID-CH₃ was 3.674 eV. A reduction in the dihedral angle post-grinding increased the T1 state energy level, leading to blue-shifted RTP emission. When the dihedral angle decreased further to 63.58°, the T₁ level rose to 3.712 eV, indicating that the excited state conformation tends to planarize after grinding or TA, favoring the blueshift of RTP emission. Moreover, the spin-orbit coupling (SOC) values for the S₁-T₂ and S₁-T₃ transitions increased and were found to be higher than those for the S₁-T₁ transition, potentially facilitating the formation of fast k_RISC, which allowed the TADF intensity to gradually increase. This mechanism explains the observed wide range of blue shift in the RTP emission peak and the gradual increase in TADF intensity of CZID-CH₃. Detailed TD-DFT results and frontier molecular orbitals for CZID-CH₃ are provided in Fig. S32 (Supporting information). It is notable that the CZID derivatives exhibit remarkable afterglow emission properties, maintaining similar emission characteristics to their solid-state forms in aqueous or strong acidic and alkaline environments without requiring any deoxidation processes (Figs. S33 and S34 in Supporting information).

  Figure 3

  

  Figure 3.  Schematic diagram of the mechanism and changes in excited state conformation after grinding stimulation of CZID-CH₃.

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  Leveraging the bright, long-lasting, and multicolor afterglow emission properties of CZID derivatives, these materials demonstrate promising potential for applications in color-adjustable light sources. Furthermore, the delayed luminescence of white light LEDs equipped with these derivatives can provide a buffer period, reducing the abrupt transition to darkness and mitigating the risk of sudden eye discomfort. We applied CZID-1-OMe@PMMA and CZID-CH₃@PMMA to the surface of white LEDs to extend the LED emission and to prepare a dimmable light source. The electroluminescence emission spectrum of the white LEDs is shown in Fig. S35 (Supporting information). Even after power disruption, the LED continues to emit yellow and red glows for several seconds (Fig. 4a). Consequently, CZID derivatives are highly effective in developing tunable light sources that offer both energy efficiency and decorative enhancements.

  Figure 4

  

  Figure 4.  Application of multicolor tunable afterglow materials. (a) Afterglow display device circuit diagram and demonstration of LED afterglow display made of CZID-1-OMe@PMMA and CZID-CH₃@PMMA. (b) Application of anti-counterfeit inks prepared by CZID and its derivatives in various situations.

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  Secondly, considering the broad absorption spectrum of CZID derivatives, innovative information encryption technologies have been developed. These technologies enable easy identification using only mobile phones, flashlights, or even natural daylight. As illustrated in Fig. 4b, safety inks formulated from CZID derivatives can be applied on various substrates such as paper, plastic or wood for anti-counterfeiting purposes. After deactivating the excitation source, which may be ultraviolet light, white light, or daylight, the surface of these materials emits strong afterglow of multi-colors that lasts for several seconds. Furthermore, CZID derivatives are nearing commercialization as cost-effective anti-counterfeiting inks. They are anticipated to be used in anti-counterfeiting labels suitable for various industrial products packaged in materials like paper, plastic, and wood.

  In conclusion, the terminal group regulation strategy employed with CZID derivatives enables dual persistent TADF and RTP emissions with highly tunable lifetimes and emission colors. Notably, the afterglow emission of these compounds can be excited by a range of light sources including ultraviolet light, visible light, and even sunlight simulator, achieving an ultra-wide range of afterglow emissions. Furthermore, the durable afterglow excited by visible light persists after mechanical grinding or even in the amorphous state after melting, indicating that the afterglow emission of these compounds is not confined to the crystalline state. Moreover, the dual persistent emission of these compounds is temperature-sensitive, suggesting potential applications in visual temperature detection and anti-counterfeiting. Crucially, these compounds also demonstrate stable ultra-long afterglow emission in both aqueous media and acid-base environments. These findings not only offer a design strategy for creating high-performance, one-component afterglow luminescent materials with multimodal emission in the amorphous state but also open new avenues for achieving high-performance afterglow under aqueous conditions and in harsh environments.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  CRediT authorship contribution statement

  Zenggang Lin: Writing – original draft, Software, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Peng Zhang: Writing – review & editing, Methodology, Investigation, Data curation. Yuzhu Yang: Software, Methodology. Weisheng Liu: Writing – review & editing, Funding acquisition, Conceptualization.

  Acknowledgment

  This work was financially supported by the National Natural Science Foundation of China (No. 21871122).

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2025.111194.

  
  
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  Figure 1  Fundamentally photophysical properties of CZID and derivatives. (a) Prompt and Delayed photoluminescence spectra of CZID and derivatives (Delay: 1 ms). (b) The CIE 1931 coordinates of delayed photoluminescence spectra for CZID and its derivatives at 410 nm excitation. (c) Delayed photoluminescence spectra of CZID-CH₃ under 254 nm and 808 nm excitation. (d) Photographs of the compounds CZID, CZID-OH, CZID-CH₃, CZID-1-OMe and CZID-3-OMe in crystalline states under white-light irradiation and at different time intervals after the removal of white-light.

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  Figure 2  Multilevel stimuli responsiveness of CZID-CH₃. (a) Temperature-dependent delayed photoluminescence spectra and (b) the CIE 1931 coordinates of CZID-CH₃ at crystal state from 273 K to 80 K (λ_ex = 410 nm, delay: 1 ms). (c) The normalized delayed photoluminescence spectra and (d) the CIE 1931 coordinates of CZID-CH₃ in crystalline state and after grinding (λ_ex = 410 nm, delay: 1 ms). (e) The normalized delayed photoluminescence spectra and (f) the CIE 1931 coordinates of CZID-CH₃ in crystalline, after TA and amorphous state (λ_ex = 410 nm, delay: 1 ms). (g) Photographs of CZID-CH₃ after grinding (300 s), TA and amorphous states under white-light irradiation and at different time intervals after the removal of white-light. (h) Prompt and delayed photoluminescence spectra of doped film CZID-CH₃@PMMA (Concentration: 2.5 wt%, λ_ex = 410 nm, delay: 1 ms).

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  Figure 3  Schematic diagram of the mechanism and changes in excited state conformation after grinding stimulation of CZID-CH₃.

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  Figure 4  Application of multicolor tunable afterglow materials. (a) Afterglow display device circuit diagram and demonstration of LED afterglow display made of CZID-1-OMe@PMMA and CZID-CH₃@PMMA. (b) Application of anti-counterfeit inks prepared by CZID and its derivatives in various situations.

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