Rigid ionic-bonding networks boosting organic room temperature phosphorescence

Domain: neuroscience
Published: 2026-01-26
Editorial outcome: major_revision

Abstract
Ionic bonds possesses excellent advantages in organic phosphorescence enhancement due to their intense electrostatic interactions, non-directional, and unsaturated characteristics. Nowadays, host-guest doping is the mainstream strategy for synthesizing room-temperature phosphorescent materials. While this strategy may suffer from compatible molecular configurations between host and guest, it needs precise molecular design and synthesis. Herein, ionic alkyl chain molecules are selected as hosts to prepare ionic phosphorescent materials handily. The host materials are suitable for diverse guests, simply attaching quaternary ammonium groups to chromophores. By altering the isolated chromophores, diverse phosphorescence colors from blue to orange-red can be emitted with long-lived lifetimes up to 572.27 ms. Consecutive ionic bonds can be formed in host-guest materials to construct ionic-bonding networks, thereby effectively restricting the movement of guest molecules and minimizing non-radiative transitions. Notably, the matching principle of the alkyl chain in the ionic host-guest system not only provides an ordered and rigid environment but also stimulates the external heavy-atom effect effectively, thus riveting chromophores for shining phosphorescence. This strategy, through the synergistic effects of host-guest doping and ionic-bonding networks, provides a reference for studying isolated-molecular phosphorescence with non-conjugated hosts.

Introduction
Organic room-temperature phosphorescence (RTP), an extraordinary optical phenomenon resulting from the radiative transition of triplet excitons in purely organic materials, has garnered significant attention due to its excellent advantages. These include prolonged emission lifetimes1, high exciton utilization efficiencies2, and diverse excited-state properties3, which enable broad applications in fields such as information encryption4, afterglow displays5, organic light-emitting diodes (OLEDs)6, and biological imaging7. Despite this potential, realizing RTP in organic materials remains a significant challenge. Weak spin-orbital coupling limits intersystem crossing (ISC) between singlet and triplet states, leading to inefficient triplet exciton generation. Furthermore, the molecular motions at room temperature often result in non-radiative decay of excitons, making it challenging to stabilize triplet excitons and achieve RTP8. To address these challenges, various strategies have been proposed. Enhancing spin-orbital coupling through the introduction of heavy atoms9,10, carbonyl groups11, and heteroatoms12 into organic chromophores has been a primary focus. Simultaneously, strategies such as crystal engineering13,14, host-guest doping15,16, self-assembly17,18, polymerization19,20, and other approaches21–23 have been employed to create rigid microenvironments that stabilize triplet excitons. Among these, most strategies have taken the construction of intermolecular interactions (e.g., lp-π and π-π interactions) as their core targets to enhance phosphorescence. Especially, lp-π interactions can promote intersystem crossing rate from singlet to triplet states and provide a rigid molecular environment to stabilize multiple triplet states, thus being more conducive to the improvement of phosphorescent properties24,25.

Nowadays, ionic bond-mediated room temperature phosphorescence has been reported continually in the form of small molecules, polymers, and host-guest doping26–30. The materials constructed by these strategies all utilize strong ionic bonds to restrict the movement of the chromophore, thereby achieving phosphorescence emission31. For example, the construction of anion-π interactions promoted the spin-orbit coupling via external heavy atom effect32, guest molecules significantly affected the arrangement of host molecules for improving phosphorescence efficiency33, chiral transfer from anionic cellulose derivatives to ionic chromophores for circularly polarized phosphorescence29 and so forth. In addition, host-guest doping has emerged as a particularly effective and versatile approach due to its straightforward preparation and tunable RTP properties. In this system, guest chromophores are dispersed within a host matrix, where the RTP originates from the guest molecules, while the host matrix provides a rigid microenvironment that suppresses non-radiative decay for achieving RTP. In particular, recent efforts in host-guest RTP materials have primarily focused on optimizing guest chromophores, leading to significant progress. Various functionalized guest molecules have been developed, resulting in RTP materials with ultralong lifetimes, high quantum yields, tunable emission colors, and other desirable properties26,34–38.

However, not only in ionic host-guest doped systems, but in nearly all molecular doping systems, the reliance on tailored host molecules remains a significant bottleneck. Effective host molecules must exhibit high singlet and triplet energy levels to prevent reverse energy transfer from guest to host and possess compatible molecular configurations and functional groups to establish strong intermolecular interactions. These stringent requirements necessitate precise molecular design and synthesis, hindering the development of universal and high-performance RTP systems. To overcome these limitations, we propose a molecular design strategy for ionic host-guest RTP materials via leveraging consecutive ionic bonds for assembling ionic-bonding networks (Fig. 1). In this approach, non-conjugated alkyl chains serve as the host matrix. These chains naturally possess higher singlet and triplet energy levels than conjugated guest phosphorescent chromophores, effectively preventing reverse energy transfer. Additionally, unlike the weak hydrogen bonding and van der Waals forces commonly observed in traditional host-guest systems, introducing ionic bonds offer excellent advantages5,39. Notably, ionic bonds can be harnessed to form rigid ionic-bonding networks between host and guest molecules via electrostatic interactions, providing notable advantages in preventing molecular motion and promoting the external heavy atom effect. Interestingly, most previous studies achieved this effect by directly adding heavy atoms, while this work accomplishes it through the matching of host-guest alkyl chains, demonstrating a different mechanism. Synergizing the rigid ionic network and efficient external heavy atom effect (Fig. 1b), this design enables the development of high-performance RTP materials with enhanced stability and emission properties. As a result, our system achieves an afterglow lifetime of 572.27 ms at room temperature. Moreover, the universal nature of these host molecules facilitates the creation of RTP materials with tunable emission colors, spanning from blue to red, demonstrating the versatility and broad applicability of this approach. This work introduces an innovative strategy that integrates the strengths of host-guest doping with ionic interactions, providing a universal platform for advancing the field of organic RTP materials. By addressing longstanding challenges in host-guest compatibility and RTP stabilization, this design not only highlights a significant leap forward in material performance but also opens avenues for the practical application of RTP in diverse fields.

Results
To validate our hypothesis, we designed and synthesized a series of quaternary ammonium-functionalized alkyl chain host molecules with varying chain lengths. Additionally, phosphorescent chromophores with different triplet excited-state energy levels were chosen as guest molecules to verify the universality of the strategy. These chromophores were further ionized by trimethylamine to form ionic networks with the ionized host through electrostatic interactions. The chemical structures and purity of guest molecules were fully characterized by nuclear magnetic resonance (NMR), high-resolution mass spectrometry (HRMS), high-performance liquid chromatography (HPLC) and elemental analyses (Supplementary Figs. 6–23 and 25–37). As a proof-of-concept, n-hexyl-hyamine (HDBr) and 6-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)-N,N,N-trimethylhexan-1-aminium bromide (NapHBr) were chosen as the host and guest molecules, respectively. The host and guest were dissolved in methanol at a weight ratio of 0.5 wt.%, and the doped material DNBr was prepared by removing the solvent through rotary evaporation. This approach is more straightforward than conventional heating and melting. As expected, upon UV excitation at 365 nm, the DNBr material displayed a yellow afterglow visible to the naked eye for several seconds after the UV light was turned off, demonstrating clear RTP behavior. The photophysical properties of the DNBr were systematically investigated. The steady-state photoluminescence (PL) spectrum revealed dual emission bands at 409, 560, and 602 nm (Fig. 2a). Following an 8 ms delay, only the long-wavelength emission bands at 560 and 602 nm persisted, indicating phosphorescence. The stability was also investigated by monitoring the continuous phosphorescence intensity at 602 nm. As shown in Supplementary Fig. 38, the emission intensity remains unchanged throughout the measurement period under continuous excitation of a 340 nm UV lamp for 1000 s, demonstrating that the DNBr phosphor exhibits excellent UV photostability and is suitable for practical applications under ambient conditions. Then, lifetime decay measurements confirmed the short-wavelength band at 409 nm corresponding to fluorescence with a lifetime of 13.9 ns (Supplementary Fig. 39). In comparison, the long-wavelength bands at 560 nm and 602 nm exhibited lifetimes of 48.50 ms and 47.72 ms, respectively, consistent with phosphorescent emission (Fig. 2b). Analysis of the NapHBr chromophore in dilute solution (1×10⁻⁵ M) at 77 K showed phosphorescence peaks at 548 nm and 594 nm (Supplementary Fig. 40), aligning closely with the emission bands of DNBr. These results confirm that the yellow RTP originates from the isolated NapHBr chromophore rather than aggregation-induced emission. Notably, only a weak fluorescence band at 364 nm was observed in the spectrum of HDBr, with no detectable phosphorescence under ambient conditions (Supplementary Fig. 41). This indicated that the ionic host primarily functions as a rigid, ionic-bonding network that immobilizes the guest molecules through a confinement effect, without directly participating in or altering their luminescent properties. Excitation wavelength-dependent PL spectra further supported this conclusion, showing consistent emission bands at 560 nm and 602 nm irrespective of the excitation wavelength (300–450 nm), indicating a single stable triplet excited state in DNBr (Fig. 2c). These results suggested that the ionized host molecules can effectively stabilize the triplet excitons of the guest chromophore to achieve phosphorescence at room temperature.

To explore the effect of guest concentration on RTP performance, we prepared host-guest doped materials with guest-to-host weight ratios ranging from 0.1 wt.% to 5.0 wt.%. All samples exhibited yellow afterglows lasting approximately 2 seconds, with phosphorescence lifetimes ranging from 27.85 ms to 48.50 ms. The optimal performance was observed at a guest-to-host weight ratio of 0.5 wt.%, yielding the longest lifetime of 48.50 ms (Supplementary Figs. 42–46). Additionally, the influence of alkyl chain length in the host molecules was investigated by synthesizing a series of host materials (BDBr, ADBr, HDBr, HeDBr, and ODBr) with varying chain lengths (Fig. 1c). Despite differences in chain length, all doped materials (BDNBr, ADNBr, DNBr, HeDNBr, and ODNBr) exhibited fluorescence and phosphorescence dual emission features in their PL spectra, with consistent phosphorescent emission bands at 560 nm and 602 nm (Fig. 2d and Supplementary Figs. 47–51). Notably, DNBr showed the highest phosphorescence-to-fluorescence intensity ratio (IPhos./IFluo.) of 2.499 and the longest lifetime of 48.5 ms. We hypothesized that this optimal performance arises from the enhanced self-assembly facilitated by matching the alkyl chain lengths of host and guest molecules, enabling the formation of a rigid ionic network through electrostatic interactions. Moreover, the bromine atoms at the end of the chains of the host molecules might also play a crucial role in accelerating the generation of triplet excitons by virtue of their heavy atom effect. To verify this speculation, we subsequently conducted a set of control experiments. When a non-ionized chromophore (Nap6C) was doped into HDBr, no long-lived RTP was observed, only a fluorescence band at 471 nm, indicating aggregated fluorescence emission due to inefficient self-assembly (Supplementary Figs. 52 and 53). Similarly, when the ionic host was replaced with a non-functionalized alkyl chain host (HBr), intense fluorescence was observed with negligible aggregated phosphorescence under ambient conditions (Fig. 2e and Supplementary Fig. 54). The doped material with non-ionic host and guest structures also exhibited fluorescence without phosphorescence (Supplementary Fig. 55). These control experiments further corroborated the critical role of ionic interactions in constructing a rigid network essential for RTP. Moreover, we also replaced the bromine atoms with chlorine in the host molecule, yielding DNCl. Compared to DNBr, DNCl exhibited decreased phosphorescence intensity in the PL spectrum (Fig. 2f) but significantly prolonged the lifetimes to 214.68 ms and 208.06 ms for the 554 nm and 596 nm emission bands, respectively (Supplementary Fig. 56). To further verify the function of the host material and the great advantages of the ionic-bonding networks, NapHBr was separately doped into various matrices, including classic oligomers and polymers. As shown in Supplementary Fig. 57, when NapHBr is doped into PVA and PEG1000, similar blue emission bands at ~400 nm can be observed in the PL spectra, which ascribes to the fluorescence of the NapHBr chromophores. However, after a delay of 8 ms, a long-wavelength emission band at ~550 nm can only be obtained from the PVA matrix, which originates from the phosphorescence of NapHBr. Whereas when in PEG1000, no phosphorescence was observed. It is worth noting that in the PVA matrix, although the strong intermolecular interaction can induce the appearance of phosphorescent components in the PL spectrum, the IPhos./IFluo. value decreased to 0.157 compared with 2.499 in HDBr. These findings highlight the significance of ionic-bonding networks and the heavy-atom effect in enhancing RTP performance. Additionally, enhancement of the rigidity in the host-guest system was also evidenced by conducting decomposition temperature experiments. We found that ionized hosts exhibited a higher decomposition temperature than their non-ionized counterparts (Supplementary Fig. 58). Specifically, for hexylamine, the thermal decomposition temperature increased obviously before and after ionization. This enhancement might be attributed to the formation of strong ionic bonds through electrostatic interactions in the host-guest system. These results suggest that the specific matching rule of alkyl chains between host and guest molecules primarily facilitates the formation of an ordered ionic bond network through electrostatic interactions, thereby enabling effective coordination of external heavy atoms. This promotes the generation and stabilization of triplet excitons, ultimately enhancing room-temperature phosphorescence (RTP).

To further elucidate the mechanism underlying room-temperature phosphorescence in the host-guest doped system, we investigated the molecular arrangements of the host and guest components within the single crystal structures. As illustrated in Fig. 3, the rationale for chain matching lies in its ability to promote the formation of highly ordered ionic-bonding networks that rigidify the microenvironment and sustain long-lived triplet excitons. Specifically, strong ionic interactions among the ionized hosts drive the assembly of a head-to-head cross-linked network, where bromine atoms in the alkyl chains act as ionic nodes to stabilize the structure (Fig. 3a). Furthermore, guest molecules are immobilized by C–H···Br (3.029 Å) and C–H···O (2.516 and 2.585 Å) interactions, which effectively suppress non-radiative motions of the chromophores (Fig. 3b). A critical factor is the near-perfect length matching of the flexible n-hexyl chains between host (8.859 Å) and guest (8.825 Å) molecules (Fig. 3c). This precise alignment enables seamless integration of chromophores into the host’s ionic framework, strengthening both ionic-bonding networks and external heavy-atom interactions with Br⁻ ions.

Subsequently, several control experiments were conducted to verify the roles of ionic-bonding networks. As shown in Supplementary Fig. 59, π–π stacking interactions (3.649 Å) between naphthyl chromophores were observed in the aggregated state. Such stacking could potentially quench the triplet excitons of NapHBr phosphors (Supplementary Figs. 60 and 61)40, emphasizing the importance of maintaining the ionic network to minimize aggregation-induced quenching. Powder X-ray diffraction (XRD) analysis further confirmed the formation of the ionic network. The experimental XRD pattern of DNBr closely matched the simulated XRD pattern of the HDBr crystal, confirming that the ionic-bonding network remains intact in the DNBr material without being adversely influenced by chromophores’ arrangement (Fig. 3d). This suggested that the DNBr microcrystal was formed by embedding guest molecules into host networks. Moreover, the obtained DNBr microcrystals were ground for 10 minutes to prepare DNBr powder. As shown in Supplementary Fig. S62, the PL and phosphorescence spectra of DNBr powder exhibited similar emission peaks compared to DNBr. While the IPhos./IFluo. decreased to 0.078 in the PL spectrum of DNBr powder, indicating that grinding destroyed the integration of host and guest. XRD analysis confirmed that the experimental XRD pattern of DNBr microcrystal closely matched the XRD pattern of DNBr powder due to good crystallization of the host (Supplementary Fig. 63). This indicated not only the ionic-bonding networks in the host but also that the assembly between host and guest molecules is crucial in enhancing phosphorescence.

Theoretical simulations supported our design rationale of ionic alkyl chain host and guest molecules. The calculated triplet energy levels for HDBr and NapHBr were 5.508 eV and 2.566 eV, respectively (Fig. 3e). This substantial energy gap indicates that energy transfer does not occur within DNBr, allowing the guest chromophores to independently exhibit RTP. Additionally, the general interaction properties function (GIPF) analysis provided insights into the nature of intermolecular interactions41. The quaternary ammonium groups predominantly contributed to the surface area with electrostatic potential (ESP) values between −20 and +20 kcal/mol. Strong negative and positive ESP regions were localized at the electric charge centers, confirming the formation of tightly cross-linked ionic-bonding networks and the confinement of chromophores (Fig. 3f). Moreover, the orbital nature of the states and spin-orbit coupling was investigated in host-guest states based on hybrid quantum mechanics and molecular mechanics (QM/MM) calculations (Supplementary Fig. 64a). It is worth noting that the alkyl chain of the guest molecule all adopted a linear structure in the host-guest doping states with negligible changes in electronic transition characteristics via the analysis of natural transition orbitals (NTOs). This indicated that the alkyl chain of the guest molecule tended to adopt a linear arrangement more readily in the host-guest doping—an arrangement that not only facilitated its insertion into the host structures but also promoted the assembly between host and guest molecules for ionic-bonding networks.

To validate the generality of the strategy, we further selected a series of phosphorescent chromophores with varying triplet excited-state energy levels as guest molecules. By incorporating n-hexyl chains via quaternary ammonium functionalization into these chromophores, we synthesized the target guest chromophores, namely 9-(carbazol-9-yl)-N,N,N-trimethylhexan-1-aminium bromide (CzHBr), N,N,N-trimethyl-6-(10H-phenothiazin-10-yl)hexan-1-aminium bromide (PTZHBr), and 6-(6-bromo-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)-N,N,N-trimethylhexan-1-aminium bromide (4BrNapHBr). We then doped these guest chromophores into the host of HDBr with a weight ratio of 0.5 wt.%. Due to the higher triplet excited-state energy level of the host and the intense ionic bonding between host and guest, the resulting host-guest doped materials exhibited long-lived phosphorescence at room temperature. As illustrated in Fig. 4a,b, the phosphorescence emission bands of the doped materials exhibit a gradual redshift from 444 nm to 620 nm as the triplet excited-state excited-state energy levels of the chromophores decrease. This results in a broad color gamut ranging from blue to orange-red phosphorescent emission. Meanwhile, the phosphorescent lifetimes of these host-guest doped materials also showed flexible tunability ranging from 5.87 ms to 572.27 ms (Fig. 4c and Supplementary Table 2). These long-lived phosphorescent emissions all originate from isolated molecular phosphorescence nature (Supplementary Fig. 68). This phenomenon is primarily attributed to the large energy gap between the host and guest molecules, which efficiently prevent reverse energy transfer (Fig. 4d). Furthermore, the significant negative and positive ESPs of the guest chromophores provided an essential prerequisite for constructing a rigid ionic network through electrostatic interactions (Fig. 4d). This network plays a crucial role in suppressing the non-radiative decay of the chromophores, thereby achieving RTP.

Given the cost-effective and readily prepared phosphorescence materials, their potential applications in information encryption were demonstrated by combining mask and squash techniques (Fig. 5a,b). Firstly, DNBr was pressed into a sheet. Upon switching on a 365 nm UV lamp, a blue maple leaf pattern can be observed through a mask (Fig. 5c, top). After cessation of 365 nm lamp excitation, a bright yellow afterglow is visible to the naked eye (Fig. 5c, bottom), which can be utilized for afterglow-based encryption. Additionally, HDBr-host was pressed into a sheet with a “2024” mask. Under 365 nm UV lamp illumination, the sheet exhibited weak fluorescence and no phosphorescence emissions (Fig. 5d, left and middle). However, after treatment with DCzBr solution, intense blue afterglow became observable (Fig. 5d, right). This indicates that the host and guest molecules can rapidly cross-link via electrostatic interactions, endowing the ionic chromophore solution with the functionality of encryption inks.

Methods
General procedures for synthesis of phosphors
1H-benzo[de]isoquinoline-1,3(2H)-dione (Nap). 1H,3H-benzo[de]isochromene-1,3-dione (1.982 g, 10 mmol) was added into 40 mL ammonium hydroxide (25%). The solution was continually stirred for 8 h at 50°C. The solvent was removed by rotary evaporation and the residue was purified by column chromatography to yield Nap (1.364 g, 69.2%) as a white solid. 1H NMR (400 MHz, DMSO-d6): δ 11.62 (s, 1H), 8.37-8.39 (d, 4H), 7.78-7.82 (t, 2H). 13C NMR (DMSO-d6): δ 164.66, 134.87, 132.11, 130.51, 129.14, 127.62, 123.01.

6-bromo-1H-benzo[de]isoquinoline-1,3(2H)-dione (4BrNap). The synthesis of 4BrNap was similar to that of Nap except that 1H,3H-benzo[de]isochromene-1,3-dione was replaced by 6-bromo-1H,3H-benzo[de]isochromene-1,3-dione (2.771 g, 10 mmol). The target molecule 4BrNap was obtained in 67.1% yield (1.853 g). 1H NMR (400 MHz, DMSO-d6): δ 11.83 (s, 1H), 8.44–8.48 (m, 2H), 8.20–8.22 (d, 1H), 8.13–8.15 (d, 1H), 7.90–7.94 (t, 1H). 13C NMR (DMSO-d6): δ 164.18, 164.07, 133.15, 131.81, 131.39, 130.76, 130.60, 130.11, 129.69, 129.25, 123.78, 123.01.

2-(6-bromohexyl)−1H-benzo[de]isoquinoline-1,3(2H)-dione (Nap6CBr). Nap (0.394 g, 2 mmol) and NaH (0.240 g, 6 mmol) were added into 30 mL DMF. The solution was stirred for 30 min at 0°C. Then, 1,6-dibromohexane (1.46 g, 6 mmol) was added to the stirred solution. After that, the solution was continually stirred for 12 h at 90°C. The solvent was removed by rotary evaporation and the residue was purified by column chromatography to yield NapHBr (0.457 g, 63.5%) as a white solid. 1H NMR (400 MHz, DMSO-d6): δ 8.40–8.45 (dd, 4H), 7.79–7.84 (q, 2H), 3.97–4.01 (t, 2H), 3.31–3.50 (t, 2H), 1.73–1.80 (p, 2H), 1.56–1.63 (q, 2H), 1.30–1.41 (m, 4H). 13C NMR (DMSO-d6): δ 163.92, 134.82, 131.81, 131.24, 127.74, 122.57, 35.67, 32.65, 29.50, 27.85, 27.81, 26.17. Analysis (calcd., found for C18H18BrNO3): C (60.01, 60.07), H (5.04, 5.074), N (3.89, 3.80). HRMS (ESI): molecular weight for 360.25, m/z found for 360.05903.

2-hexyl-1H-benzo[de]isoquinoline-1,3(2H)-dione (Nap6C). The synthesis of Nap6C was similar to that of Nap6CBr except that 1,6-dibromohexane was replaced by 1-bromohexane (0.990 g, 6 mmol). The target molecule Nap6C was obtained in 47.0% yield (0.264 g). 1H NMR (400 MHz, DMSO-d6): δ 8.21–8.27 (dd, 4H), 7.64–7.68 (t, 2H), 3.83–3.87 (t, 2H), 1.46–1.50 (p, 2H), 1.17 (s, 6H), 0.72–0.76 (h, 3H). 13C NMR (DMSO-d6): δ 163.79, 134.73, 131.73, 131.15, 127.65, 122.46, 40.11, 31.48, 27.92, 26.72, 22.51, 14.42. Analysis (calcd., found for C18H19NO2): C (76.84, 76.06), H (6.81, 6.29), N (4.98, 4.82).

4-bromo-2-(6-bromohexyl)−1H-benzo[de]isoquinoline-1,3(2H)-dione (4BrNap6CBr). The synthesis of 4BrNap6CBr was similar to that of Nap6CBr except that Nap was replaced by 4BrNap (0.552 g, 2 mmol). The target molecule 4BrNap6CBr was obtained in 35.9% yield (0.315 g). 1H NMR (400 MHz, DMSO-d6): δ 8.43–8.48 (m, 2H), 8.22–8.24 (m, 1H), 8.12–8.14 (m, 1H), 7.89–7.93 (m, 1H), 3.94–3.97 (m, 2H), 3.46–3.50 (m, 2H), 1.73–1.80 (p, 2H), 1.55–1.62 (dp, 2H), 1.28–1.43 (m, 4H). 13C NMR (DMSO-d6): δ 163.35, 163.30, 133.07, 132.06, 131.84, 131.44, 130.24, 129.61, 129.29, 128.74, 123.22, 122.44, 35.66, 32.65, 29.51, 27.80, 27.76, 26.16. Analysis (calcd., found for C18H17Br2NO2): C (49.23, 50.99), H (3.90, 4.363), N (3.19, 2.90). HRMS (ESI): molecular weight for 439.15, m/z found for 437.19311.

10-(6-bromohexyl)−10H-phenothiazine (PTZ6CBr). The synthesis of PTZ6CBr was similar to that of Nap6CBr except that Nap was replaced by phenothiazine (0.398 g, 2 mmol). The target molecule PTZ6CBr was obtained in 32.6% yield (0.236 g). Following the similar synthetic procedure for Nap6CBr, the target molecule PTZ6CBr was obtained (0.236 g, 32.6%). 1H NMR (400 MHz, DMSO-d6): δ 7.08-7.16 (m, 4H), 6.86-6.95 (m, 4H), 3.77-3.80 (t, 2H), 3.39-3.41 (t, 2H), 1.58-1.71 (dq, 4H), 1.30-1.32 (m, 4H). 13C NMR (DMSO-d6): δ 145.31, 128.09, 127.65, 124.24, 122.94, 116.33, 46.85, 35.46, 32.69, 27.66, 26.58, 25.82. Analysis (calcd., found for C18H20BrNS): C (59.67, 59.84), H (5.56, 5.397), N (3.87, 3.72), S (8.85, 8.442). HRMS (ESI): molecular weight for 362.33, m/z found for 362.05674.

9-(6-bromohexyl)−9H-carbazole (Cz6CBr). The synthesis of Cz6CBr was similar to that of Nap6CBr except that Nap was replaced by Cz (0.334 g, 2 mmol). The target molecule Cz6CBr was obtained in 63.2% yield (0.417 g). 1H NMR (400 MHz, DMSO-d6): δ 8.08–8.11 (t, 2H), 7.51–7.55 (t, 2H), 7.37–7.43 (dd, 2H), 7.12–7.17 (dd, 2H), 4.28–4.33 (m, 2H), 3.88–3.40 (d, 2H), 1.60–1.73 (m, 4H), 1.20–1.34 (m, 4H). 13C NMR (DMSO-d6): δ 140.49, 126.20, 122.56, 120.79, 119.17, 109.72, 42.60, 35.52, 32.66, 28.86, 27.80, 26.12. Analysis (calcd., found for C18H20BrN): C (65.46, 66.27), H (6.10, 5.93), N (4.24, 4.11). HRMS (ESI): molecular weight for 330.27, m/z found for 330.08490.

NapHBr, 4BrNapHBr, PTZHBr and CzHBr. Nap6CBr, 4BrNap6CBr, PTZ6CBr and CzHBr (1 mmol) were added into 30 mL THF with 5 mL NH3 (2 mol/L in THF), respectively. The solutions were stirred for 6 h at room temperature. As a result, white target molecules can be obtained after filtering, washing and drying.

NapHBr. 1H NMR (400 MHz, CD3OD-d4): 8.51–8.53 (dd, 2H), 8.32–8.34 (dd, 2H), 7.77–7.81 (dd, 2H), 4.12–4.16 (m, 2H), 3.31–3.36 (m, 2H), 3.11 (s, 9H), 1.72–1.85 (ddt, 4H), 1.45–1.53 (m, 4H). 13C NMR (CD3OD-d4): δ 163.80, 135.73, 132.18, 130.83, 127.60, 122.30, 66.47, 66.44, 52.16, 39.56, 27.28, 26.07, 25.52, 22.35. Analysis (calcd., found for C21H27BrN2O2): C (60.15, 59.87), H (6.49, 6.78), N (6.68, 6.39). HRMS (ESI): molecular weight (M-Br) for 339.46, m/z found for 339.20641.

4BrNapHBr. 1H NMR (400 MHz, CD3OD-d4): δ 8.55 (s, 1H), 8.53–8.54 (d, 1H), 8.30–8.32 (d, 1H), 8.07–8.09 (d, 1H), 7.85–7.89 (dd, 1H), 4.09–4.13 (m, 2H), 3.32-3.36 (m, 2H), 3.12 (s, 9H), 1.71-1.85 (m, 4H), 1.45-1.54 (m, 4H). 13C NMR (CD3OD-d4): δ 163.66, 136.01, 132.94, 131.61, 131.17, 130.87, 130.41, 129.76, 128.72, 128.14, 123.15, 122.15, 66.40, 52.18, 39.72, 27.23, 26.07, 25.59, 22.36. Analysis (calcd., found for C21H26Br2N2O2): C (50.62, 50.59), H (5.26, 5.57), N (5.62, 5.43). HRMS (ESI): molecular weight (M-Br) for 418.36, m/z found for 419.11448.

PTZHBr. 1H NMR (400 MHz, CD3OD-d4): δ 7.07–7.17 (m, 4H), 6.87–6.96 (m, 4H), 3.87–3.94 (dt, 2H), 3.19–3.24 (m, 2H), 3.03 (s, 9H), 1.63–1.79 (m, 4H), 1.29–1.53 (m, 4H). 13C NMR (CD3OD-d4): δ 145.48, 127.22, 126.99, 125.19, 122.27, 115.70, 66.36, 52.18, 46.32, 26.10, 25.75, 25.47, 22.43. Analysis (calcd., found for C21H29BrN2S): C (59.85, 59.56), H (6.94, 7.21), N (6.65, 6.52), S (7.61, 7.38). HRMS (ESI): molecular weight (M-Br) for 341.54, m/z found for 341.20436.

CzHBr. 1H NMR (400 MHz, CD3OD-d4): δ 7.20–7.24 (m, 2H), 6.56–6.64 (m, 4H), 6.31–6.36 (m, 2H), 4.06 (s, 9H), 3.42–3.53 (m, 2H), 0.82–1.06 (m, 4H), 0.36–0.57 (m, 6H). 13C NMR (CD3OD-d4): δ 139.65, 124.56, 121.90, 118.97, 117.68, 107.79, 51.26, 41.31, 32.16, 27.67, 26.77, 25.48, 21.48. Analysis (calcd., found for C21H29BrN2): C (64.78, 64.85), H (7.51, 7.48), N (7.19, 7.08). HRMS (ESI): molecular weight (M-Br) for 309.48, m/z found for 309.23212.

Preparation of doped materials (DNBr, DCzBr, DPBr, DBrNBr)
Taking the host-guest doping ratio of 0.5 wt.% as an example, the guest (NapHBr, 4BrNapHBr, PTZHBr and CzHBr, 2 mg) and host (HDBr, 400 mg) were dissolved in 10 mL CH3OH. The solution was thoroughly shaken to ensure uniform mixing of the host and guest materials. Then, the solvent was removed by rotary evaporation and the ionic-doped materials were obtained as a white solid.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript presents an innovative strategy for enhancing room-temperature phosphorescence (RTP) in organic\nmaterials via the construction of rigid ionic-bonding networks. The authors employed alkyl chains functionalized with\nquaternary ammonium groups as universal ionic hosts, effectively addressing the molecular compatibility issue in\nconventional host–guest systems. With a high degree of experimental rigor and theoretical support, the study demonstrates\nlong-lived phosphorescence (up to 572.27 ms), wide color tunability, and practical applications in information encryption.\nSome issues should be addressed as follows:\n1. Experimental procedure requires some more details. Critical experimental conditions are not sufficiently detailed. For\nreproducibility, please expand the Materials and Methods or Supplementary Information accordingly.\n2. Figure 2e uses a different vertical axis scale or unit compared to other subfigures (e.g., 2a, 2f), which may mislead readers\nwhen comparing emission intensities.\n3. Novelty needs clearer distinction from prior work. While the integration of ionic bonding and external heavy atom effect is\npromising, similar concepts have been reported recently. The manuscript would benefit from a more explicit comparison with\nthese studies to highlight its unique contributions.\n4. UV photostability under prolonged excitation was not examined. These are important for practical applications and should\nbe addressed.\n5. Mass spectrometry data is missing for newly synthesized compounds and should be included. Several newly synthesized\nmolecules are central to the study. While NMR and single-crystal analyses are reported, molecular weight confirmation via\nmass spectrometry (e.g., ESI-MS or MALDI-TOF) is not provided. For organic phosphorescent materials, confirming\nmolecular integrity is essential for structural verification and subsequent photophysical correlation. It is strongly\nrecommended to include high-resolution MS data for all key intermediates and final products in the Supplementary\nInformation to ensure the completeness of molecular characterization.", "reviewer_2": "This manuscript presents a novel and practical strategy for the development of RTP materials. The authors\ninnovatively\nemploy ionic alkyl chain-based molecules as hosts and introduce quaternary ammonium groups to guest chromophores,\nenabling a facile host–guest doping approach. This method effectively overcomes the common limitations associated with\nprecise host–guest molecular compatibility, offering a more universal and accessible platform for RTP material construction.\nThe manuscript is well-structured, the experimental results are convincing, and the mechanistic insights are clearly\narticulated. The synergistic effect of host–guest doping and ionic interactions represents a significant conceptual\nadvancement in the design of non-conjugated RTP systems. Given the originality and potential impact of this work, I strongly\nrecommend its publication in Nature Communications. Specific comments are provided below.\n1. The current work focuses primarily on the doped host–guest systems; however, a detailed characterization of the intrinsic\nphotophysical behavior of the ionic host materials is absent. Given the potential influence of the host matrix on the\nsuppression of non-radiative decay and triplet state stabilization, it is essential to include the photoluminescence and\nphosphorescence spectra of the pure host materials under identical measurement conditions.\n2. The authors successfully demonstrated the critical role of ionic interactions by comparing systems with and without\ncharged groups. To further substantiate this point, it would be valuable to report the luminescent behavior of a control host–\nguest system in which both components are non-ionic. Such a comparison would help isolate the contribution of ionic\nbonding to the observed phosphorescence enhancement.\n3. In Supplementary Figure 36, the measurement conditions for NapHBr are not clearly stated. Additionally, a comparison\nbetween its 77 K phosphorescence and that of the DNBr-doped system under ambient conditions would be informative.\n4. Long-term stability under ambient conditions is critical for RTP applications. Continuous emission tracking of DNBr would\nenhance the study’s relevance.", "reviewer_3": "The manuscript by Tu et al. investigates the creation of afterglow materials aimed at extending triplet lifetimes to several\nhundred milliseconds. The authors synthesized ionic alkyl chain molecules as hosts for ionic phosphorescent materials,\nincorporating quaternary ammonium groups into the chromophores. By modifying isolated chromophores, they achieved\nphosphorescence colors ranging from blue to orange red, with lifetimes reaching 572.27 ms. They assert that matching the\nalkyl chain in the ionic host–guest system provides a rigid, ordered environment. Combined with the external heavy atom\neffect, this arrangement stabilizes chromophores for prolonged phosphorescence. The strategy, they claim, relies on the\nsynergistic effects of host-guest doping and ionic bonding networks to enhance triplet stability. While the concept of\nionic bonding-mediated afterglow enhancement is established, the efficiency of other host–guest systems already exceed one\nsecond. This limits the novelty of their findings. Based on the design approach and reported performance, this work does not\nmeet the standards required for publication in this journal. The topic may be more appropriate for a publication focused on\nsupramolecular materials. The authors would need to address significant concerns before the manuscript could be\nconsidered suitable for its intended venue.\n1. Recent literature on ionic bond-mediated room-temperature phosphorescence (RTP) must be discussed and\nappropriately cited. The reported RTP lifetime is less impressive when compared with published studies involving host–\nguest systems. The author should reference relevant works demonstrating superior afterglow performance, such as the ionic\npolymer matrix (https://doi.org/10.1002/anie.202108025), ion-regulated RTP (Chem. Sci., 2024, 15, 4222–4237), and H-\nbonding interaction studies (https://doi.org/10.1021/acs.jpclett.4c03707).\n2. The introduction should include a discussion on lp–π and π–π interactions, citing examples from J. Phys. Chem. C 2019,\n123, 22104–22103, and J. Phys. Chem. Lett., 2018, 9, 3808–3813.\n3. PL studies of new guests in different hosts, ranging from traditional oligomers to polymeric systems, should be conducted\nfor performance comparison.\n4. The energy gap of the sole emitter and any variation with host-guest combinations should be reported. The discussion\nmust address the orbital nature of the states, spin-orbit coupling, quantum yield of intersystem crossing, and rates of non-\nradiative processes to substantiate claims.\n5. The rationale for chain matching as a means of enhancing triplet lifetimes requires clear explanation.\n6. Crystal structures should be provided, along with PL studies on crystals for comparison with powder samples.\n7. XRD patterns for both powder and crystal samples must be included, with differences related to PL behavior discussed.\n8. The minimal lifetime improvement upon increasing emitter concentration (27.85 ms to 48.50 ms) should be analysed.\nAdditional PL studies on varied hosts, as noted earlier, are recommended.\n9. HPLC and elemental analyses of new materials must be presented to confirm purity.\n10. In Supplementary Figure 40, the phosphorescence spectra of 4BrNapHBr in dilute solution exhibit multiple peaks, which\nshould be clarified."}, "author_response": "Point-by-Point Response to Reviewers\nReviewer #1:\nThis manuscript presents an innovative strategy for enhancing room-temperature phosphorescence (RTP)\nin organic materials via the construction of rigid ionic-bonding networks. The authors employed alkyl\nchains functionalized with quaternary ammonium groups as universal ionic hosts, effectively addressing the\nmolecular compatibility issue in conventional host-guest systems. With a high degree of experimental rigor\nand theoretical support, the study demonstrates long-lived phosphorescence (up to 572.27 ms), wide color\ntunability, and practical applications in information encryption. Some issues should be addressed as follows:\nComment #1: Experimental procedure requires some more details. Critical experimental conditions are\nnot sufficiently detailed. For reproducibility, please expand the Materials and Methods or Supplementary\nInformation accordingly.\nResponse: We appreciate the reviewer for the careful review. We have expanded on some more detailed\nexperimental conditions and procedures in the Revised Manuscript and Supplementary Information,\nincluding synthetic procedures for intermediates and final products, as well as the preparation of doped\nmaterials. Moreover, more detailed characterization methods (Supplementary Figs. 11-14 and 23-27), such\nas high-resolution mass spectrometry (HRMS), high-performance liquid chromatography (HPLC), and\nelemental analysis, were also conducted to demonstrate the high reproducibility of these materials.\nComment #2: Figure 2e uses a different vertical axis scale or unit compared to other subfigures (e.g., 2a,\n2f), which may mislead readers when comparing emission intensities.\nResponse: We truly understand the reviewer’s concern. The doped materials DNBr and DNCl all exhibited\nstrong PL and phosphorescence intensities. Hence, in Figures 2a and 2f, the emission intensities were\nnormalized to illustrate the emission peaks in a qualitative context. While a different vertical axis scale,\nused in Figure 2e, was intended to demonstrate in quantitative perspective that intense fluorescence\nwas observed with extremely weak aggregated phosphorescence under ambient conditions\n(Supplementary Fig. 44). Notably, the luminescence intensities of different samples cannot be compared\ndirectly based on spectral emission intensities because the spectral intensity can be affected by factors\nsuch as the amount of sample and the slit size of the spectrometer during the measurement. We hope our\nclarifications are acceptable.\nSupplementary Figure 44. a, Normalized steady-state PL (dashed gray line) and phosphorescence\nspectra (solid red line) of HNBr excited at 340 nm. b, Phosphorescence spectrum of HNBr excited at 340\nnm with non-normalized treatment.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nComment #3: Novelty needs clearer distinction from prior work. While the integration of ionic bonding\nand external heavy atom effect is promising, similar concepts have been reported recently. The manuscript\nwould benefit from a more explicit comparison with these studies to highlight its unique contributions.\nResponse: We thank the reviewer for raising the point regarding novelty. While the general concept of\nionic stabilization has indeed been reported, our work establishes a fundamentally different design strategy.\nRather than relying on simple ionic salts or rigid crystalline hosts, we deliberately engineered alkyl chain–\nmatched ionic host–guest systems. In this study, we introduce a versatile and modular approach for creating\nhigh-performance organic RTP materials using a universal ionic host-guest doping method. In this method,\nnon-conjugated alkyl chains act as the host matrix. These chains naturally possess higher singlet and triplet\nenergy levels than conjugated guest phosphorescent chromophores, effectively preventing reverse energy\ntransfer. Furthermore, unlike the weak hydrogen bonds and van der Waals interactions typical in traditional\nhost-guest systems, the consecutive ionic bonds in this work form ionic-bonding networks, providing\nnotable advantages in preventing molecular motion and promoting the external heavy atom effect.\nInterestingly, most previous studies achieved this effect by directly adding heavy atoms, while this work\naccomplishes it through the matching of host-guest alkyl chains, demonstrating a different mechanism. Not\nonly are the ionic-bonding networks formed by ionic nodes (Fig. S1a and S1b), but the quaternary\nammonium alkyl chain matching principle in the host/guest structures (Fig. S1c) is also crucial in inhibiting\nnon-radiative transitions of the chromophores, thereby enabling phosphorescence. This precise chain-\nlength matching creates an ordered and confined ionic microenvironment, which effectively stabilizes\nchromophores and minimizes nonradiative losses. Importantly, the observed performance arises from a\nsynergistic mechanism: ionic confinement suppresses vibrational dissipation, while the external heavy atom\neffect accelerates intersystem crossing. This dual regulation not only extends the triplet lifetime to 572 ms\nbut also enables broad color tunability from blue to orange-red. Our contribution addresses a\ncomplementary challenge: to achieve color-tunable, solution-processable, and structurally modular ionic\nafterglow materials. We therefore believe our work represents a clear conceptual and methodological\nadvance, providing a new supramolecular strategy with broad implications. The relevant sections of the\nrevised manuscript include these discussions, and we hope the reviewer will find them acceptable.\nFigure S1. a, Molecular stacking of host HDBr. b, Molecular stacking of guest NapHBr. c, Alkyl chain\nlengths of host and guest in crystal structures.\nComment #4: UV photostability under prolonged excitation was not examined. These are important for\npractical applications and should be addressed.\nResponse: We appreciate the reviewer's insightful comment. In response, we conducted an investigation\ninto the UV photostability of the DNBr phosphor under prolonged excitation. The sample was\ncontinuously irradiated using a 340 nm UV lamp for 1000 seconds under ambient conditions, and the\nphosphorescence intensity at 602 nm was monitored over time. As shown in Supplementary Figure 28, the\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nemission intensity remains unchanged throughout the measurement period, demonstrating that the DNBr\nphosphor exhibits excellent UV photostability and is suitable for practical applications under ambient\nconditions.\nSupplementary Figure 28. Phosphorescence intensity stability of DNBr phosphor under continuous\nUV-excitation for 1000 s.\nComment #5: Mass spectrometry data is missing for newly synthesized compounds and should be\nincluded. Several newly synthesized molecules are central to the study. While NMR and single-crystal\nanalyses are reported, molecular weight confirmation via mass spectrometry (e.g., ESI-MS or MALDI-TOF)\nis not provided. For organic phosphorescent materials, confirming molecular integrity is essential for\nstructural verification and subsequent photophysical correlation. It is strongly recommended to include\nhigh-resolution MS data for all key intermediates and final products in the Supplementary Information to\nensure the completeness of molecular characterization.\nResponse: We appreciate the valuable comments by the reviewer. As suggested, high-resolution mass\nspectrometry (HRMS) data for the newly synthesized molecules were added to the revised Supplementary\nInformation (Supplementary Figures 11-14 and 23-26).\nSupplementary Figure 11. HRMS of Nap6CBr.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nSupplementary Figure 12. HRMS of 4BrNap6CBr.\nSupplementary Figure 13. HRMS of PTZ6CBr.\nSupplementary Figure 14. HRMS of Cz6CBr.\nSupplementary Figure 23. HRMS of NapHBr.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nSupplementary Figure 24. HRMS of 4BrNapHBr.\nSupplementary Figure 25. HRMS of PTZHBr.\nSupplementary Figure 26. HRMS of CzHBr.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nReferee #2:\nThis manuscript presents a novel and practical strategy for the development of RTP materials. The authors\ninnovatively employ ionic alkyl chain-based molecules as hosts and introduce quaternary ammonium\ngroups to guest chromophores, enabling a facile host-guest doping approach. This method effectively\novercomes the common limitations associated with precise host-guest molecular compatibility, offering a\nmore universal and accessible platform for RTP material construction. The manuscript is well-structured,\nthe experimental results are convincing, and the mechanistic insights are clearly articulated. The synergistic\neffect of host-guest doping and ionic interactions represents a significant conceptual advancement in the\ndesign of non-conjugated RTP systems. Given the originality and potential impact of this work, I strongly\nrecommend its publication in Nature Communications. Specific comments are provided below.\nComment #1: The current work focuses primarily on the doped host-guest systems; however, a detailed\ncharacterization of the intrinsic photophysical behavior of the ionic host materials is absent. Given the\npotential influence of the host matrix on the suppression of non-radiative decay and triplet state\nstabilization, it is essential to include the photoluminescence and phosphorescence spectra of the pure\nhost materials under identical measurement conditions.\nResponse: We appreciate the reviewer's valuable comments. To gain deeper insight into the role of the\nhost matrix in suppressing non-radiative decay and stabilizing the triplet state, we measured the\nphotoluminescence (PL) and phosphorescence spectra of the host HDBr. As shown in Supplementary\nFigure 31, only a weak fluorescence emission at 364 nm was observed, with no detectable\nphosphorescence under ambient conditions. These results indicate that the ionic host primarily functions\nas a rigid, ionic-bonding network that immobilizes the guest molecules through a confinement effect,\nwithout directly participating in or altering their luminescent properties.\nSupplementary Figure 31. Steady state photoluminescence (PL, dashed grey line) and phosphorescence\nspectra (solid red line) of host HDBr excited at 300 nm.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nComment #2: The authors successfully demonstrated the critical role of ionic interactions by comparing\nsystems with and without charged groups. To further substantiate this point, it would be valuable to report\nthe luminescent behavior of a control host-guest system in which both components are non-ionic. Such a\ncomparison would help isolate the contribution of ionic bonding to the observed phosphorescence\nenhancement.\nResponse: We understand the point made by the reviewer. To confirm the role of ionic interactions in\nenhancing phosphorescence performance, we further made a comparison by using the non-ionic guest and\nhost. As shown in Supplementary Figure 45, the resulting doped material exhibited fluorescence with an\nemission peak located at 405 nm, which coincided with the fluorescence peak of DNBr (Fig. 2a). However,\nno detectable phosphorescence was observed under ambient conditions. This result suggests that a rigid\nionic network plays a crucial role in restricting the molecular motions of guest chromophores, thereby\ngenerating room-temperature phosphorescence.\nSupplementary Figure 45. Steady state PL (dashed grey line) and phosphorescence spectra (solid red\nline) of doped material with non-ionic host and guest structures.\nComment #3: In Supplementary Figure 50, the measurement conditions for NapHBr are not clearly stated.\nAdditionally, a comparison between its 77 K phosphorescence and that of the DNBr-doped system under\nambient conditions would be informative.\nResponse: We appreciate the reviewer for the careful review. We have provided a detailed measurement\nof the conditions of NapHBr in Supplementary Figure 50. Moreover, the phosphorescence spectrum of\nNapHBr powder was also measured at 77 K. As shown in Supplementary Figure 51, two emission peaks\nat 475 and 597 nm were observed in the phosphorescence spectrum. Specifically, the emission at 597 nm\nwas attributed to the aggregated-state phosphorescence emission of chromophores, which arose from the\nstacking effect of chromophores in the solid state (Supplementary Figure 49). In contrast, the emission\npeak at 475 nm overlapped with the aggregated-state fluorescence peak in DN phosphor (Supplementary\nFigure 42), indicating that it was a triplet-triplet annihilation (TTA) emission.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nSupplementary Figure 51. Phosphorescence spectrum of NapHBr powder excited at 340 nm at 77 K.\nComment #4: Long-term stability under ambient conditions is critical for RTP applications. Continuous\nemission tracking of DNBr would enhance the study’s relevance.\nResponse: We appreciate the valuable comments by the reviewer. As suggested by the reviewer, we\ninvestigated the stability of the sample by monitoring phosphorescence intensity under continuous\nirradiation by a UV lamp. When DNBr phosphor was continuously excited using a 340 nm UV lamp for\n1000 seconds under ambient conditions, the peak intensity at 602 nm showed no obvious change, indicating\nthat the DNBr phosphor exhibits good stability, making it suitable for long-term use under ambient\nconditions (Supplementary Figure 28).\nSupplementary Figure 28. Phosphorescence intensity stability of DNBr phosphor under continuous\nexcitation for 1000 s.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nReferee #3:\nThe manuscript by Tu et al. investigates the creation of afterglow materials aimed at extending triplet\nlifetimes to several hundred milliseconds. The authors synthesized ionic alkyl chain molecules as hosts for\nionic phosphorescent materials, incorporating quaternary ammonium groups into the chromophores. By\nmodifying isolated chromophores, they achieved phosphorescence colors ranging from blue to orange red,\nwith lifetimes reaching 572.27 ms. They assert that matching the alkyl chain in the ionic host-guest system\nprovides a rigid, ordered environment. Combined with the external heavy atom effect, this arrangement\nstabilizes chromophores for prolonged phosphorescence. The strategy, they claim, relies on the synergistic\neffects of host-guest doping and ionic bonding networks to enhance triplet stability. While the concept of\nionic bonding-mediated afterglow enhancement is established, the efficiency of other host-guest systems\nalready exceed one second. This limits the novelty of their findings. Based on the design approach and\nreported performance, this work does not meet the standards required for publication in this journal. The\ntopic may be more appropriate for a publication focused on supramolecular materials. The authors would\nneed to address significant concerns before the manuscript could be considered suitable for its intended\nvenue.\nResponse: We sincerely thank the reviewer for the thoughtful comments regarding the novelty of our\nionic strategy. We would like to clarify that our work goes beyond the general concept of ionic stabilization\nand establishes a new design logic for afterglow materials. In previous studies, ionic interactions were\nmostly introduced in a rather auxiliary manner, where simple salts or crystalline matrices\noffered some degree of rigidification but lacked precise structural control (J. Am. Chem. Soc.\n2025, 147, 11098; Angew. Chem. Int. Ed. 2025, 64, e202415042; Adv. Mater. 2025, 37, 2503074; Nat. Commun.\n2024, 15, 7149; Adv. Mater. 2024, 36, 2410739; etc.). In contrast, our system deliberately integrates alkyl\nchain engineering into the ionic host–guest framework. By carefully matching the alkyl chain length of host\nand guest, we created an ordered ionic microenvironment that enforces chromophore alignment,\nminimizes vibrational dissipation, and provides a unique level of spatial confinement not observed in earlier\nsystems. Moreover, the novelty of our approach lies in the synergistic mechanism: the external heavy atom\neffect alone cannot account for the observed performance, but when combined with the ionic-bonding\nnetwork, the two processes mutually reinforce each other—heavy atom modulation accelerates\nintersystem crossing, while ionic confinement stabilizes the triplet excitons. This dual regulation is what\nenables both long lifetimes and broad spectral tunability. In fact, by modifying isolated ionic chromophores\nwith quaternary ammonium groups, we successfully achieved multicolor phosphorescence spanning from\nblue to orange-red with lifetimes up to 572 ms. Compared with earlier ionic systems, which generally\ndisplayed single-color afterglow, our strategy provides a versatile platform with clear generalizability.\nWe recognize that certain crystalline or polymeric host–guest systems can exhibit lifetimes beyond\none second; however, such systems often prioritize lifetime extension at the cost of tunability and\nmodularity. Additionally, phosphorescence lifetime is strongly related to the intrinsic properties\nof chromophores. For example, as shown in Figure S2, NapHBr in dilute solution (1 × 10-5 M) at 77 K\nexhibited the phosphorescence peak at 548 nm with a phosphorescence lifetime of 1.49 ms. The\nphosphorescence performance of the prepared doped material, DNBr, is significantly enhanced by the\nconstruction of ionic-bonding networks. The phosphorescence lifetime can reach up to 48.50 ms, exhibiting\na 32-fold enhancement compared with that of NapHBr in MeOH at 77 K. A Chromophore with a short\nintrinsic lifetime (in dilute solution at 77 K) can achieve an extension of the phosphorescence lifetime via\nthis strategy. These results indicate that our proposal plays a crucial role in enhancing phosphorescence.\nOur contribution, therefore, addresses a different but equally important challenge: to achieve structurally\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nprogrammable, color-tunable, and solution-processable ionic phosphorescent materials that can be readily\nadapted for diverse applications in optoelectronics and information encryption. In conclusion, this\nmanuscript should not be regarded as a repetition of established ionic stabilization concepts, but rather as\nthe first demonstration of a structurally precise ionic host–guest strategy that couples chain-engineered\nconfinement with heavy atom regulation. We believe this represents a significant conceptual and\nmethodological advance, offering new opportunities for designing functional afterglow materials with broad\nimpact across supramolecular chemistry and materials science.\nFigure S2. Lifetime decay profiles of guest NapHBr at 77 K in MeOH (a) and doped material DNBr under\nambient conditions (b).\nComment #1: Recent literature on ionic bond-mediated room-temperature phosphorescence (RTP) must\nbe discussed and appropriately cited. The reported RTP lifetime is less impressive when compared with\npublished studies involving host-guest systems. The author should reference relevant works demonstrating\nsuperior afterglow performance, such as the ionic polymer matrix\n(https://doi.org/10.1002/anie.202108025), ion-regulated RTP (Chem. Sci., 2024, 15, 4222-4237), and H-\nbonding interaction studies (https://doi.org/10.1021/acs.jpclett.4c03707).\nResponse: We appreciate the reviewer's critical comments. As suggested, relevant discussions and\nliterature have been added in the Revised Manuscript.\nComment #2: The introduction should include a discussion on lp–π and π–π interactions, citing examples\nfrom J. Phys. Chem. C 2019, 123, 22104–22103, and J. Phys. Chem. Lett., 2018, 9, 3808–3813.\nResponse: We appreciate the valuable comments of the reviewer. We sincerely apologize for overlooking\nthe crucial role of lp-π and π-π interactions in enhancing room temperature phosphorescence\nperformance. Recently, most strategies have taken the construction of intermolecular interactions (e.g. lp-\nπ and π-π interactions) as their core targets to enhance phosphorescence. Notably, lp-π interactions can\npromote intersystem crossing rate from singlet to triplet states and provide a rigid molecular environment\nto stabilize multiple triplet states, thus being more conducive to the improvement of phosphorescent\nproperties (J. Phys. Chem. C 2019, 123, 22104; J. Phys. Chem. Lett. 2018, 9, 3808). Hence, the introduction of\nmultiple lp-π interactions, as well as π-π interactions, will be beneficial in facilitating highly efficient\nphosphorescence. The above discussions have been added in the Revised Manuscript.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nComment #3: PL studies of new guests in different hosts, ranging from traditional oligomers to polymeric\nsystems, should be conducted for performance comparison.\nResponse: We appreciate the reviewer’s comments. As suggested by the reviewer, we doped the guest\nchromophores of NapHBr into various matrices, including classic oligomers, polymers, and ionized alkyl\nchains, as well as investigated their photophysical properties accordingly. As shown in Figure S3, when\nNapHBr is doped into PVA, PEG1000, and HDBr, similar blue emission bands at around 400 nm can be\nobserved in the photoluminescence spectra, which are ascribed to the fluorescence of the NapHBr\nchromophores. However, after a delay of 8 ms, a long-wavelength emission band at approximately 550 nm\ncan only be obtained from the PVA and HDBr matrix, which originates from the phosphorescence of\nNapHBr. Whereas when in PEG1000, no phosphorescence was observed. These results indicate that ionic\nbonds and hydrogen bonds between chromophores and the matrix can effectively suppress the non-\nradiative decay of triplet excitons, thereby enabling the generation of room-temperature phosphorescence.\nNotably, compared to doping into the PVA matrix, the matrix of ionized HDBr showed a substantial\nincrease in the proportion of phosphorescent components in the PL spectrum (Fig. S3c). The value of\nI /I can be up to 2.499, which is higher than the 0.157 in PVA (Table S1), which contributes to the\nPhos. Fluo.\nsynergistic mechanism combining ionic networks with the external heavy atom effect.\nFigure S3. Normalized steady state PL (dashed line) and phosphorescence (solid line) spectra of doped\nmaterials with hosts PEG1000 (a), PVA (b) and HDBr (c).\nTable S1. I /I values of NapHBr in different hosts.\nPhos. Fluo.\nSample I /I\nPhos. Fluo.\nNapHBr in PEG1000a -\nNapHBr in PVA 0.157\nNapHBr in HDBr 2.499\naexhibiting no phosphorescence\nComment #4: The energy gap of the sole emitter and any variation with host-guest combinations should\nbe reported. The discussion must address the orbital nature of the states, spin-orbit coupling, quantum\nyield of intersystem crossing, and rates of non-radiative processes to substantiate claims.\nResponse: We see the point raised by the reviewer. As suggested, we clarified the energy gaps of the sole\nemitter and any variation with host-guest combinations clearly. As shown in Figure S4a, NapHBr\nchromophore in dilute solution (1 × 10⁻⁵ M) at 77 K showed phosphorescence peaks at 548 nm and 594\nnm. Upon any variation with host-guest combinations, NapHBr chromophore exhibited similar\nphosphorescence spectra with emission peaks located at ~560 and ~602 nm (Figure S4b-S4f), aligning\nclosely with the emission bands of NapHBr in single-molecule states. The similar emission peaks indicated\nthat the triplet energy gaps of the sole emitter and any variation with host-guest combinations were\ninvariable. Then, the orbital nature of the states and spin-orbit coupling was investigated in host-guest\nstates based on hybrid quantum mechanics and molecular mechanics (QM/MM) calculations\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\n(Supplementary Figure 54). It is worth noting that the alkyl chain of the guest molecule all adopted a linear\nstructure in the host-guest doping states with negligible changes in electronic transition characteristics via\nthe analysis of natural transition orbitals (NTOs). This indicated that the alkyl chain of the guest\nmolecule tended to adopt a linear arrangement more readily in the host-guest doping—an\narrangement that not only facilitated its insertion into the host structures but also promoted the assembly\nbetween host and guest molecules for ionic-bonding networks. Besides, rates of intersystem crossing (k )\nisc\nand non-radiative processes (k ) were also calculated through experimental data (Supplementary Table 1).\nnr\nThe values of k were on the order of 106-107 (per second). And the non-radiative transition rates of\nisc\nphosphorescence exhibited an order-of-magnitude decrease compared with that of fluorescence. Taken\nabove theoretical calculations, we concluded that the formation of ionic-bonding networks in the doped\nmaterials provided favorable conditions for the realization of ionic phosphorescence.\nFigure S4. Phosphorescence spectra of sole emitter and any variation with host-guest combinations.\nSupplementary Figure 54. Calculated spin-orbit couplings (ξ) and natural transition orbitals (NTOs) of\nchromophores in host-guest states via QM/MM calculations.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nSupplementary Table 1. Dynamic photophysical parameters of DNBr, DCzBr, DPBr and DBrNBr\nphosphors.\nFluorescence Phosphorescence\nWavelength\nPhosphor τ Ф k Fluo. k τ Ф k Phos.\n(nm) Fluo nr isc Phos. nr\n(ns) (%) (s-1)a (s-1)b (ms) (%) (s-1)c\n409 13.9 2.07 6.55×107 4.99×106 - - -\nDNBr\n602 - - - - 47.72 6.93 19.50\n369 3.96 19.76 1.66×108 3.62×107\nDCzBr\n422 - - - - 572.27 14.34 1.50\n450 4.29 1.34 1.28×107 9.70×106 - -\nDPBr\n523 - - - - 31.91 4.16 30.03\n429 3.40 2.05 2.76×108 1.16×107 - - -\nDBrNBr\n620 - - - - 5.87 3.95 163.63\na)kFluo (1  )/ ; b)k  / ; c)kPhos (1 )/\nnr Fluo Phos Fluo isc Phos Fluo nr Phos Phos\nComment #5: The rationale for chain matching as a means of enhancing triplet lifetimes requires clear\nexplanation.\nResponse: We appreciate the reviewer’s comments. As shown in Supplementary Figure S1, the rationale\nfor chain matching lies in its ability to promote the formation of highly ordered ionic-bonding networks\nthat rigidify the microenvironment and sustain long-lived triplet excitons. Specifically, strong ionic\ninteractions among the ionized hosts drive the assembly of a head-to-head cross-linked network, where\nbromine atoms in the alkyl chains act as ionic nodes to stabilize the structure. Within this network, guest\nmolecules are further immobilized by C–H···Br (3.029 Å) and C–H···O (2.516 and 2.585 Å) interactions,\nwhich effectively suppress non-radiative motions of the chromophores. A critical factor is the near-perfect\nlength matching of the flexible n-hexyl chains between host (8.859 Å) and guest (8.825 Å) molecules\n(Supplementary Fig. S1c). This precise alignment enables seamless integration of chromophores into the\nhost’s ionic framework, strengthening both ionic bonding and external heavy-atom interactions with Br⁻\nions. When the alkyl chain lengths are mismatched, guests fail to embed within the host lattice, leading to\nweakened interactions and significantly reduced phosphorescence. By contrast, in the matched system\n(DNBr), chain complementarity ensures a well-ordered ionic microenvironment and efficient host–guest\ncoupling, thereby delivering superior triplet lifetimes (Supplementary Fig. 41).\nFigure S1. a, Molecular stacking of host HDBr. b, Molecular stacking of guest NapHBr. c, Alkyl chain\nlengths of host and guest in crystal structures.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nSupplementary Figure 41. Lifetimes of doped materials with different alkyl chains.\nComment #6: Crystal structures should be provided, along with PL studies on crystals for comparison\nwith powder samples.\nResponse: We truly understand the reviewer’s concern. We have provided the crystal structures of host\nHDBr and guest NapHBr. However, due to the low doping concentration of guest molecules, the crystal\nstructure of the doped material cannot be readily obtained, and the specific stacking of guest molecules\nwithin the host structure cannot be determined via single-crystal X-ray diffraction analysis. Nevertheless,\nwe performed XRD measurements of the doped material DNBr. The experimental XRD pattern of\nDNBr exhibits a high degree of consistency with the simulated XRD pattern derived from\nthe HDBr crystal structure (Figure S5a), confirming that the ionic-bonding network remains intact in\nthe DNBr without being adversely influenced by chromophores' arrangement. Meanwhile, we successfully\ndetermined the single-crystal structure of the guest NapHBr. Comparing the structures of a single host\nmolecule and a single guest molecule revealed that their alkyl chain lengths are 8.859 and 8.825 Å,\nrespectively (Figure S5b), indicating a close size match. This structural feature further confirmed\nthat guest molecules can be embedded into host structure to form microcrystals.\nFurthermore, as suggested by the reviewer, the obtained DNBr microcrystals were ground for 10\nminutes to prepare DNBr powder. As shown in Figure S6, the PL and phosphorescence spectra of DNBr\npowder exhibited similar emission peaks compared to DNBr. While the I /I decreased to 0.078 in the\nPhos. Fluo.\nPL spectrum of DNBr powder, indicating that grinding destroyed the integration of host and guest, which\nin turn led to a reduction in phosphorescence intensity. These results suggest that the ionic bands between\nhost and guest play a crucial role in forming ordered and rigid ionic networks, which suppress the non-\nradiative transition of guest chromophores.\nFigure S5. a, The X-ray diffraction patterns of DNBr (experimental) and HDBr (simulated), respectively.\nb, Alkyl chain lengths of host and guest in crystal structures.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nFigure S6. Photophysical characterizations of DNBr (a) and DNBr treated with grinding (b) under\nambient conditions.\nComment #7: XRD patterns for both powder and crystal samples must be included, with differences\nrelated to PL behavior discussed.\nResponse: We appreciate the reviewer’s comments. We have demonstrated that grinding destroyed the\nintegration of host and guest, as noted in Comment #6. XRD patterns further confirmed our hypothesis.\nAs shown in Figure S7, the experimental XRD pattern of DNBr microcrystal closely matched the XRD\npattern of DNBr powder due to good crystallization of host. These indicated not only the ionic-bonding\nnetworks in the host but also that the assembly between host and guest molecules are crucial in enhancing\nphosphorescence.\nFigure S7. The X-ray diffraction patterns of DNBr and DNBr treated with grinding, respectively.\nComment #8: The minimal lifetime improvement upon increasing emitter concentration (27.85 ms to\n48.50 ms) should be analysed. Additional PL studies on varied hosts, as noted earlier, are recommended.\nResponse: We gratefully acknowledge the reviewer’s insightful comments. With increasing emitter\nconcentration, the phosphorescence lifetimes initially increased from 27.85 to 48.50 ms and subsequently\ndecreased to 35.57 ms (Supplementary Fig. 36, bottom). This trend can be attributed to the relatively low\nchromophore content under dilute conditions, where the sparse distribution of chromophores results in\nboth weak phosphorescent intensity (Supplementary Fig. 36, top) and a shortened emission lifetime. Upon\nmoderate concentration enhancement, the proportion of chromophores in the monomeric state increased,\nthereby promoting a significant rise in phosphorescent intensity and a concomitant extension of the\nlifetime. However, as evidenced in Supplementary Figure 50, chromophores in aggregated states are non-\nemissive due to phosphorescence quenching. Further elevation of concentration promotes aggregation,\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nwhich suppresses radiative decay pathways and results in a decline in observed lifetimes. Through this\nconcentration-dependent analysis, the optimal host–guest doping ratio can be precisely identified, providing\na robust basis for subsequent in-depth investigation of photophysical behavior.\nAs suggested by the reviewer, we doped the guest chromophores of NapHBr into various matrices,\nincluding classic oligomers, polymers, and ionized alkyl chains, as well as investigated their photophysical\nproperties accordingly. As shown in Figure S3, when NapHBr is doped into PVA, PEG1000, and HDBr,\nsimilar blue emission bands at around 400 nm can be observed in the photoluminescence spectra, which\nare ascribed to the fluorescence of the NapHBr chromophores. However, after a delay of 8 ms, a long-\nwavelength emission band at approximately 550 nm can only be obtained from the PVA and HDBr matrix,\nwhich originates from the phosphorescence of NapHBr. Whereas when in PEG1000, no phosphorescence\nwas observed. These results indicate that ionic bonds and hydrogen bonds between chromophores and\nthe matrix can effectively suppress the non-radiative decay of triplet excitons, thereby enabling the\ngeneration of room-temperature phosphorescence. Notably, compared to doping into the PVA matrix, the\nmatrix of ionized HDBr showed a substantial increase in the proportion of phosphorescent components\nin the PL spectrum (Fig. S3c). The value of I /I can be up to 2.499, which is higher than the 0.157 in\nPhos. Fluo.\nPVA (Table S1), which contributes to the synergistic mechanism combining ionic networks with the\nexternal heavy atom effect.\nSupplementary Figure 36. I /I (top) and lifetimes (bottom) of doped materials with various\nPhos. Fluo.\nconcentrations.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nSupplementary Figure 50. Steady-state PL (black line) and phosphorescence spectra (red line) of\nNapHBr powder excited at 340 nm under ambient conditions.\nFigure S3. Normalized steady state PL (dashed line) and phosphorescence (solid line) spectra of doped\nmaterials with hosts PEG1000 (a), PVA (b) and HDBr (c).\nTable S1. I /I values of NapHBr in different hosts.\nPhos. Fluo.\nSample I /I\nPhos. Fluo.\nNapHBr in PEG1000a -\nNapHBr in PVA 0.157\nNapHBr in HDBr 2.499\naexhibiting no phosphorescence\nComment #9: HPLC and elemental analyses of new materials must be presented to confirm purity.\nResponse: Thanks for the valuable review by this reviewer. According to the reviewer, high-performance\nliquid chromatography (HPLC) and elemental analyses were conducted to confirm the purity of the target\nguest materials. As shown in Supplementary Figure 27, NapHBr, CzHBr, PTZHBr, and 4BrNapHBr all\nexhibited one peak in HPLC spectra, demonstrating the high purity of the target guests. Elemental analyses\nfurther verified this. A comparative analysis was conducted on the measured contents of C, H, N, and S\nelements against their theoretical values (Table S2), and the results showed that the deviations fell within\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nthe acceptable error range. These data indicate that the guest molecules in this work exhibited high purity,\nmeeting the requirements for subsequent studies on their phosphorescent properties.\nSupplementary Figure 27. HPLC spectra of NapHBr, CzHBr, PTZHBr and 4BrNapHBr.\nTable S2. Elemental analyses of NapHBr, CzHBr, PTZHBr and 4BrNapHBr.\nElement (calcd., found) C (%, %) H (%, %) N (%, %) S (%, %)\nNapHBr 60.15, 59.87 6.49, 6.78 6.68, 6.39 -\nCzHBr 64.78, 64.85 7.51, 7.48 7.19, 7.08 -\nPTZHBr 59.85, 59.56 6.94, 7.21 6.65, 6.52 7.61, 7.38\n4BrNapHBr 50.62, 50.59 5.26, 5.57 5.62, 5.43 -\nComment #10: In Supplementary Figure 58, the phosphorescence spectra of 4BrNapHBr in dilute\nsolution exhibit multiple peaks, which should be clarified.\nResponse: We gratefully acknowledge the reviewer’s comments. At 77 K, molecular motions, including\nvibrations and rotations, were effectively suppressed, enabling the observation of multiple emission peaks\nfrom the chromophores of 4BrNapHBr. These peaks arise from radiative transitions among different\nvibrational sublevels within the lowest triplet excited state. As shown in Figure S8, the radiative transition\nspectra of phosphorescent materials can be analyzed based on the Franck-Condon principle (J. Phys. Chem.\n1990, 94, 4420). Distinct vibrational progressions typically accompany the radiative decay of an organic\nphosphorescent material. Ideally, when the T state exhibits a nearly identical structure to the S state\n1 0\n(molecular vibronic coupling is negligible), the resulting emission spectrum is very narrow, with only a 0-0\nvibration peak (Fig. S8, left). An increase in structural differences between the S and T states can induce\n0 1\nbroadening of the emission spectrum (Fig. S8, middle), which is attributed to the involvement of vibrational\nprogressions separated by characteristic vibrational frequencies. For vibrational modes that are strongly\ncoupled to structural changes, the corresponding vibrational progressions may even lead to multiple\nemission peaks (Fig. S8, right). Notably, owing to charge redistribution in the excited state, structural\nchanges of the material are inevitable. Hence, the phosphorescence spectra of 4BrNapHBr in dilute\nsolution exhibit multiple peaks.\nSubmitted to Nature Communications (Manuscript No. NCOMMS-25-47925)\nFigure S8. Franck-Condon emission spectra profiles for different vibrational modes."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The author has reponded all my questions, I do not have any further comments.", "reviewer_2": "Since the authors have made detailed revisions based on the comments of the reviewers, I agree that the manuscript is\naccepted for publication.", "reviewer_3": "The authors have effectively addressed the reviewer’s concerns, and the revised manuscript shows substantial\nimprovement. I agree with Reviewer 2 that the novelty of the work remains somewhat uncertain, as similar studies have\nreported high triplet lifetime. However, the authors have made a reasonable attempt to propose a broader conceptual\napproach by controlling alkyl chains through ionic interactions and exploiting the heavy atom effect. While the effort\nenhances the manuscript’s clarity and depth, the issue of originality persists. I leave the final decision regarding its suitability\nfor publication to the editorial team."}, "author_response": "Submitted to Nature Communications (Manuscript No. NCOMMS-25-47925A)\nPoint-by-Point Response to Reviewers\nReviewer #1:\nThe author has responded all my questions, I do not have any further comments.\nResponse: We express our sincere gratitude again to the reviewer for valuable comments.\nReferee #2:\nSince the authors have made detailed revisions based on the comments of the reviewers, I agree that the\nmanuscript is accepted for publication.\nResponse: We sincerely thank the reviewer for positive comments.\nReferee #3:\nThe authors have effectively addressed the reviewer’s concerns, and the revised manuscript shows\nsubstantial improvement. I agree with Reviewer 2 that the novelty of the work remains somewhat\nuncertain, as similar studies have reported high triplet lifetime. However, the authors have made a\nreasonable attempt to propose a broader conceptual approach by controlling alkyl chains through ionic\ninteractions and exploiting the heavy atom effect. While the effort enhances the manuscript’s clarity and\ndepth, the issue of originality persists. I leave the final decision regarding its suitability for publication to\nthe editorial team.\nResponse: We sincerely express our thanks to the reviewer for the thoughtful comments that have\nenriched our work."}]

Decision letter