All-solid passive organic optical limiter via coordination-bond anchoring strategy

Domain: neuroscience
Published: 2026-04-12
Editorial outcome: major_revision

Abstract
Organic optical limiters are vital for protecting human eyes and sensitive optics against laser radiation, offering exceptional optical properties, and ultrafast responses. However, their practical applications are hindered by aggregation-caused quenching and photodegradation in the solid state. Here, we proposed an ingenious all-solid, passive optical limiter via high-elastic-state thermo-compression, integrating indium phthalocyanine anchored to functional moieties within polymer microspheres. The key innovation lay in the coordination-bond anchoring strategy, which effectively suppressed indium phthalocyanine aggregation and facilitated the intersystem crossing. The resulting device demonstrated exceptional limiting performance, with a giant nonlinear absorption coefficient (4.80 × 10-5 m/W) and an ultralow optical limiting threshold (< 0.013 J/cm2) at 532 nm, originating from long-lived triplet carrier accumulation. Moreover, the device exhibited excellent mechanical robustness and practical protection capability, as applied in smartphone camera. This work provided a viable strategy toward high-performance, practical organic solid optical limiter for next-generation laser protection applications.

Introduction
Despite advances in laser technology propelling the current photonic era, accidental exposure to high-intensity radiation poses severe risks to human eyes and sensitive optical sensor1,2. Current active protection methods, which rely on devices such as liquid crystal3, spatial light modulators4, laser detectors5, and frequency agile filters6 that physically isolate specific laser wavelengths, are often constrained by continual energy consumption and slow response times7. In this regard, optical limiters based on nonlinear optical (NLO) properties, as a passive strategy, maintain high transparency under low-intensity incident light (open state), while instantaneously becoming opaque upon exposure to high-intensity radiation (off state), resolving this dilemma8. The dynamic transparency without external energy fundamentally distinguished passive optical limiting (OL) from wavelength-selective active protection systems. Meanwhile, benefiting from rapid response speed, high linear transparency, and broad spectral protection range, the optical limiters are emerging as indispensable tools for laser safety. Over recent years, significant efforts have been dedicated to various types of inorganics (metal sulfides9, MXene10), organics (phthalocyanines11, porphyrins12), and inorganic-organic materials (hybrid halide perovskites13,14, covalent organic framework15,16, metal-organic frameworks17,18) to fabricate ideal optical limiters.

Among these materials, phthalocyanines (Pcs) stand out as particularly promising systems due to excellent OL properties. Crucially, the advantages of Pcs directly originate from their unique molecular architecture: a metallomacrocyclic structure centered around a metal ion, characterized by a planar conjugated system with 18π-electrons and four isoindole subunits attached via meso positioned nitrogen atoms19. Compared with inorganic optical limiters20,21, the structural flexibility and the possibility of functionalizing various organic and inorganic elements into the Pcs framework effectively enlarge the optical window and enhance the OL response22-24. In structural modifications, strategies such as ligand functionalization and host-guest assembly have been proven effective in modulating optical behaviors of metal-macrocyclic clusters25,26, while metal atom incorporation enhanced third-order NLO properties in 2D/3D Pcs-based COFs27.

Furthermore, blending, covalent functionalization, and MOF/COSF encapsulation have realized ultrafast NLO responses across different wavelengths28,29. However, given aggregation and poor photostability (as manifested by photodegradation) caused by π-π interactions and radiation-induced chemical reactions remained intractable , which continued to hinder the practical application of Pc-based optical limiters30-32.

Herein, we proposed a robust strategy to bridge the gap between high-performance molecules and practical devices by spatially confining indium phthalocyanine (InPc) within functionalized polymer microspheres to realize all-solid passive optical limiters (PMOL). Distinct from conventional physical doping, our approach utilized amino- and hydroxyl-functionalized polymers to anchor InPc molecules via coordination bonds. This molecular-level engineering not only effectively suppressed aggregation-induced quenching and photodegradation but also modulated the electronic structure. As elucidated by density functional theory (DFT) calculations, the coordinated InPc derivatives exhibited enhanced intersystem crossing (ISC), leading to superior intrinsic NLO performance compared to their pristine InPc. Furthermore, the microspheres were integrated into all-solid device via high-elastic-state thermo-compression. This technique created a 3D nanostructured network through the mutual entanglement of surface molecular chains, which preserved the integrity of the sensitive InPc while endowing the PMOL with high linear transparency and exceptional mechanical robustness. Z-scan measurements confirmed that this synergistic design yielded a substantial nonlinear absorption coefficient and an ultralow optical limiting threshold. Thus, the coordination-based anchoring strategy successfully addressed long-standing challenges related to aggregation and photodegradation in Pcs systems, offering a viable pathway for next-generation laser protection, optical communication, and photoelectric sensing.

Results
Figure 1a illustrated the fabrication process of the PMOL based on polymer microspheres. Cross-linked InPc-P(MMA-co-DMAEA)-PEGMA OL microspheres were synthesized via emulsion polymerization of methyl methacrylate (MMA), dimethyl aminoethyl acrylate (DMAEA) and poly(ethylene glycol) monoacrylate (PEGMA) with InPc. During synthesis, coordination bonds formed between InPc and functional groups (amino/hydroxyl) via lone-pair electron donation to the empty orbitals of the indium (In) ion, anchoring InPc within microspheres. This interaction significantly enhanced its optical properties and promoted uniform distribution. Subsequent high-elastic-state thermo-compression assembled intact microspheres into PMOL. This resulting 3D structure provided suitable mechanical strength through the intertwinement of molecular chains on the microspheres’ surfaces. As a prototype for lasering protective eyeglasses, PMOL demonstrated excellent visible light imaging and highlighted laser protection capabilities (Fig. 1b).

To analyze the performance of the PMOL, the OL and mechanical properties of six samples were investigated and compared experimentally: 200 nm/300 nm microspheres and InPc concentrations (0.3, 0.5, and 0.7 wt.%; Supplementary Fig. 1). Among these, the 200-7 (200 nm microspheres with 0.7 wt.% InPc) PMOL exhibited preferable comprehensive performance. In the Z-scan experiment, the PMOL were positioned on a motorized translation stage for precise Z-axis scanning (Fig. 1c). Remarkably, the giant nonlinear absorption coefficient (β = 4.80 × 10−5 m/W eff at wavelength of 532 nm) of the PMOL (200-7) was obtained, which represented a 104-fold enhancement over pure InPc33 (2.22 × 10−9 m/W) and surpassed the highest reported value for other phthalocyanine materials by ≈ 3 orders of magnitude27,33-43. (Fig. 1d and Supplementary Table 1). Moreover, compared with other classes of OL materials (Supplementary Table 2), the PMOL demonstrated competitive nonlinear absorption performance while maintaining a combination of high linear transparency, robust mechanical integrity, and scalable processability.

To investigate the influence of coordination bonds on the molecular electronic structure of InPc, DFT calculations were performed on pristine InPc and its amino- (InPc-N) and hydroxyl-coordinated (InPc-O) derivatives44 (Fig. 2). Electrostatic potential mapping (Fig. 2a) showed that N or O coordination redistributes electron density around the In center, forming electron-rich domains. The NLO performance of Pcs was governed by the carrier density at the triplet state (T1) level45 (Fig. 2b), which was generally accounted for the five energy levels model in the excited state. Crucially, the efficiency of populating T1 via ISC relied on the energy gap between the S1 and T1 states. The calculated excited states (Fig. 2c) revealed that both InPc-N and InPc-O possessed a narrower energy gap compared to pristine InPc. This narrower gap, synergizing with the enhanced spin-orbit coupling form coordination, lowered the barrier for ISC and boosted the S1 to the T1 transition rate46,47. The resulting triplet accumulation enhanced excited-state absorption (T1 → Tn), when its cross-section exceeded that of ground-state absorption, thereby strengthening reverse saturable absorption (RSA) under intense irradiation. Consequently, high-intensity light was attenuated more effectively, leading to a lower limiting threshold and subsequently improved NLO performance.

The morphology of InPc, OL microspheres and PMOL was characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). While InPc formed aggregated clusters (~500 nm) in solution (Fig. 2d), coordination bond anchoring enabled a more uniform distribution of InPc-rich nanodomains within OL microspheres (Fig. 2e, f). Energy dispersive X-ray spectroscopy (EDS) mapping and corresponding EDS spectra (Supplementary Fig. 2) clearly showed indium signals co-localized with the observed nanodomains. Moreover, PMOL microspheres exhibited denser packing than those in solution due to interfacial entanglement during thermo-compression (Fig. 2f and Supplementary Fig. 3). Furthermore, to demonstrate the thermal stability and the relationship with internal microstructure of material, thermogravimetric (TG) analysis was conducted (Supplementary Fig. 4a, b). Interestingly, enhanced thermal stability occurred at 0.5 wt% InPc content, attributable to competing intermolecular force and heat conduction effects. After that, OL microspheres were also investigated through differential scanning calorimetry (DSC) experiment and the glass transition temperature (Tg) were all over 100 ℃ (Fig. 2g and Supplementary Fig. 4c), critical for high-elastic-state thermo-compression formation. Intermolecular restriction of polymer chains at 0.5 wt% InPc yielded the highest Tg in this work, with lower concentrations providing insufficient reinforcement and higher concentrations slightly mitigating the effect through increased thermal conductivity48. Moreover, the Fourier Transform Infrared (FT-IR) spectra of six PMOL were obtained to identify the functional groups (Fig. 2h and Supplementary Fig. 4d). Aromatic C-N heterocyclic units and C=C bond was found in the range of 1200-1400 cm -1 and 1640-1670 cm-1, respectively49,50, which demonstrated that MMA, DMAEA and PEGMA double bonds reacted to form polymer microspheres containing InPc. From the point of view of InPc activity, the Raman spectra of PMOL, solid PMMA and OL microspheres in solution were characterized through laser micro-Raman spectrometer (Fig. 2i and Supplementary Fig. 5). Compared with solid PMMA, PMOL peaked at 680, 1500 and 1600 cm-1 were assigned to the In-N/In-O, C-N/C=N and C=C bonds, respectively51,52, confirming In coordination with amino and hydroxyl groups within the PMOL. Moreover, the PMOL and OL microspheres in solution exhibited characteristic peaks at 1500 and 1600 cm-1, while the 680 cm-1 signal was absent in solution-phase microspheres, indicating the photodegradation-induced deactivation of encapsulated InPc. Conversely, InPc maintained excellent activity in the PMOL, enabling sustained OL effects.

X-ray photoelectron spectroscopy (XPS) was deployed to elucidate the chemical anchoring state and the mechanism of coordinate-bond formation53,54. The full scan survey spectrum (Fig. 3a) confirmed C, N, O, and In as the dominant surface elements of OL microspheres and PMOL. Critically, high-resolution analysis (Fig. 3b) provided direct evidence for the material's structure and coordination environment. The C 1s signals confirmed the copolymer structure, in agreement with FT-IR data (Fig. 2h), while the O 1s and N 1s spectra revealed decisive O-In and N-In bonds, respectively (Fig. 3b and Supplementary Fig. 6). Furthermore, the well-defined In3+ doublet with symmetric, unbroadened peaks indicated that InPc molecules remained uniformly dispersed and chemically active due to effective coordination anchoring. The impact of the thermo-compression process extended beyond macroscopic densification. It induced a microstructural reorganization that strengthens interfacial coordination. This enhancement was evidenced by a ∼0.4 eV positive shift in the binding energy of the In center in the PMOL sample compared to the microspheres (Supplementary Table 3), a trend consistent with FT-IR and X-ray diffraction results (Supplementary Fig. 7). Additionally, the narrowing of the full width at half maximum for the C and O peaks suggested that the applied temperature and pressure led to a more uniform overall electronic structure in PMOL.

The UV-vis transmittance and absorption spectra demonstrated the interaction between the PMOL and low-intensity light within a broad wavelength band (Fig. 3c, Supplementary Fig. 8, and Supplementary Fig. 9). Typical absorption of B bands and Q bands for Pcs in visible regions were observed, corresponding to S0 → S1 transitions from different vibrational and rotational energy levels55,56. A broader absorption bandwidth in the PMOL compared to the DFT-calculated molecular spectra (Fig. 3c, Supplementary Fig. 8a, and 8b), an effect attributed to fabrication process. The main B bands and Q bands of the 200-x PMOL were broadened as the concentration of InPc increased, owing to the enhanced response to light. Interestingly, the 300-5 PMOL showed the broadest B bands and Q bands among the 300-x groups, likely from InPc aggregated-state formation57.

The third-order NLO properties of the PMOL were characterized by nanosecond (ns) open-aperture Z-scan at 532 nm. As depicted in Fig. 3d and Supplementary Fig. 10a, the normalized transmittance decreased as the sample approached the focal point (Z = 0), reaching a minimum at the focus. This valley-shaped response was a hallmark of RSA27,36. RSA intensified with higher InPc concentrations in all PMOL except 300-5, where aggregation impaired NLO performance. To ensure the accuracy of the nonlinear absorption measurements, potential artifacts were further ruled out. The pure PMMA substrate exhibited a constant normalized transmittance (T ≈ 0.99), and the closed-aperture Z-scan curves displayed highly symmetric peak-valley profiles (Supplementary Fig. 11a and b). These two observations confirmed that the signals in the open-aperture Z-scan arise primarily from nonlinear absorption rather than nonlinear scattering or refraction. Furthermore, the nonlinear absorption coefficients (βeff) of PMOL were calculated from the open-aperture Z-scan curves, which were presented in Supplementary table 4. The structure of PMOL was conducive to improving the NLO response and enabling enhanced OL performance while maintaining the activity of InPc.

To investigate the OL properties, PMOL were positioned precisely at the focal point within the optical path and the input-output fluence data were systematically recorded (Fig. 3e and Supplementary Fig. 10b). The results indicated that the PMOL demonstrated superior OL performance under intense laser irradiation, characterized by a high linear transmittance (Tlin) and low threshold (FOL, intensity at 50% of Tlin) at 532 nm (Supplementary Table 5). Interestingly, the OL effect depended on coupled InPc concentration and microsphere size. For 200-x PMOL, the effect dominated at higher concentrations, while 300-x PMOL exhibited complex nonlinearity. Both Tlin and FOL exhibited fluctuating changes since larger-sized microspheres might facilitate the formation of aggregated InPc. Meanwhile, the 300-5 PMOL exhibited distinctive performance attributed to the formation of aggregation of InPc which triggered a sharp decline in Tlin and excited state quenching57. Overall, the 200-7 PMOL achieved preferable NLO performance (βeff = 4.80 × 10−5 m/W, Tlin = 59.13%, FOL < 0.013 J/cm2) by virtue of coordination-bond anchoring strategy, which concurrently ensured uniform InPc dispersion, enhanced photostability, and promoted the OL-facilitating ISC. It is worth noting that the 200-7 PMOL exhibited an ultra-low FOL at 532 nm laser and a giant βeff exceeding other reported Pcs materials (Supplementary Table 1 and 6). Moreover, the energy-dependent Z-scan of 200-7 PMOL (5 nJ-14 μJ) demonstrated practical RSA limiting sensitivity (Supplementary Fig. 11c and d). While negligible changes were observed at low energies (5-10 nJ), a pronounced valley emerged at ~50 nJ. This valley deepened and eventually saturated at higher energies, indicating a trend consistent with excited-state absorption (ESA)-dominated RSA under ns excitation27.

To elucidate the underlying mechanism of the enhanced NLO response, femtosecond transient absorption spectroscopy (fs-TAS) was employed to probe the photoinduced carrier dynamics within the PMOL. Upon excitation at 625 nm (Q bands), the 3D fs-TAS map (Fig. 3f) of 200-7 PMOL revealed ground state bleach (GSB) at 670-720 nm (Q bands) and ESA at specific delays, with spectral signatures contrasting as negative (blue/green) and positive (orange/yellow) signals, respectively. Significantly, the carrier dynamics mechanism was revealed by the 2D fs-TAS (Fig. 3g). Within the 0-3 ns window, the ESA signals did not decay to the baseline but instead maintained a robust amplitude. This persistent non-zero offset indicated that a significant population of carriers was retained in a long-lived excited state. Furthermore, as revealed by the global fitting results, a dominant lifetime of ~268 ps was identified as a sub-nanosecond transient reasonably reflecting the ISC process46. The kinetic traces (Fig. 3h) revealed the early stages of the photophysical process. The initial ultrafast spectral evolution was attributed to the onset of ISC process and vibrational relaxation. Subsequently, the spectral evolution of the ESA, combined with the unrecovered signal amplitude, served as strong evidence for efficient ISC demonstrating the enhanced population transfer from S1 state to T1 state. To track the final relaxation of this long-lived species, ns-TA measurements were conducted under 380 nm excitation (Supplementary Fig. 12). The decay dynamics were well-fitted by a mono-exponential function, yielding a lifetime of 512 ns, a value consistent with recent observations for Pcs58. The resulting spectra displayed features consistent with the final state observed in fs-TAS, confirming the long-lived species as the T1 state. The rigid environment provided by the coordination bonding restricted molecular motion, effectively suppressing non-radiative decay pathways and thereby extending the triplet lifetime. Critically, the enhanced NLO performance of PMOL was driven from the accumulation of excited electrons in the long-lived T1 state, enabling strong ESA-dominated OL.

Robust mechanical properties were essential for PMOL applications. Nanoindentation, minimally invasive and suitable for small volumes, was thus used to characterize key properties (hardness, elastic modulus, contact stiffness) via load/unload curves (Supplementary Fig. 13 and 14). To ensure statistical reliability and properly assess data distribution, measurements were conducted at four spatially distinct locations on each of the six samples (n = 4), with the extracted parameters presented as mean values ± standard deviations (SD). The 200-7 PMOL exhibited robust mechanical properties (Hardness = 0.363 ± 0.004 GPa, Modulus = 5.81 ± 0.03 GPa, Stiffness = (5.02 ± 0.01)  104 N/m), attributable to its close-packed microstructure. Atomic force microscopy (AFM) analysis of residual indentations revealed a depth of only 248 nm, indicating > 85% elastic recovery upon unloading (Supplementary Fig. 15), confirming exceptional resilience of PMOL crucial for practical applications.

Practical imaging systems are vulnerable to accidental high-intensity laser exposure. To demonstrate the protective capability of the PMOL via its RSA-based energy regulation, a comparative assessment was conducted using a smartphone camera system: a protected camera (p-camera) equipped with the PMOL (200-7) and an unprotected camera (b-camera) without PMOL. Fig. 4a-f presented photographic comparisons of postcards captured by p-camera and b-camera, including images under laser irradiation and post-irradiation conditions. The p-camera yielded clearly resolvable images despite overall bluish tinting (Fig. 4a). During laser exposure, the p-camera image (Fig 4b) showed no damage, contrasting with the distinct purple line observed in the b-camera (Fig. 4e). After 1-minute laser irradiation, the p-camera remained undamaged (Fig. 4c) whereas b-camera images showed ~6 mm dot damage (Fig. 4f). These results confirmed that the PMOL effectively shielded sensors from high-intensity lasers while maintaining visible-light imaging clarity. Beyond OL, the PMOL also exhibited superior thermal management capabilities, as revealed by infrared thermal imaging. The maximum temperature of PMOL on the p-camera rose 36% (21.5 ℃ → 29.3 ℃) during 6-min irradiation but dropped 1.4 ℃ within 10 s post-exposure (Fig. 4g). Conversely, temperature of b-camera rose 40% (20.9 ℃ → 29.3 ℃) with negligible cooling (Fig. 4h), confirming the rapid heat dissipation and thermal management superiority of PMOL. Microscopic inspection of the CCD chips provided the final evidence (Fig. 4i). After 20 minutes of laser irradiation, the unprotected CCD chip clearly exhibited a damage layer caused by high energy compared with the protected CCD chip. Collectively, these findings validated the exceptional OL and heat dissipation performance of the PMOL, showcasing its immense potential for real-world optoelectronic protection.

Methods
Materials
Methyl methacrylate (MMA, monomer; 99%, Sinopharm Chemical Reagent Co., Ltd., China), dimethyl ethyl acrylate (DMAEA, monomer; Sinopharm Chemical Reagent Co., Ltd., China), poly(ethylene glycol) monoacrylate (PEGMA, monomer; Sinopharm Chemical Reagent Co., Ltd., China), indium(III) phthalocyanine chloride (InPc) powder were obtained from Shanghai MERYER Biochemical Technology Co., Ltd. Potassium persulfate (KPS; Sinopharm Chemical Reagent Co., Ltd., China) as an initiator, sodium dodecyl sulfate (SDS; Sinopharm Chemical Reagent Co., Ltd., China) as an emulsifier, and deionized water as the polymerization medium were used.

Preparation of Cross-Linked P(MMA-co-DMAEA)-PEGMA OL Microspheres
Cross-linked P(MMA-co-DMAEA)-PEGMA OL microspheres were synthesized by emulsion copolymerization, as shown in Fig. 1. Take, for example, the 200 nm OL microspheres with concentration of InPc = 0.5 wt.%. 0.0011 g of SDS was dissolved in 150 mL of deionized water in a 250 mL, three-necked, round-bottom flask equipped with a polytetrafluoroethylene-bladed paddle stirrer, a condenser, a nitrogen gas inlet, and a thermometer. At the same time, the mixture of MMA (9 g), DMAEA (0.5 g), and PEGMA (0.5 g) doped with the InPc (0.05 g) was dispersed uniformly using an ultrasonic cleaner for 3-10 min in an ice bath to avoid aggregation of InPc. Subsequently, the mixture was added into a flask deoxygenated by bubbling nitrogen gas in the flask at room temperature for 5 min, followed by heating at 75 ℃. When the temperature stabilized at 75 ℃ for 30 min, 0.1 g of KPS (i.e., 1 wt.% of the reagent) was introduced to initiate polymerization, and polymerization was performed at 75 ℃ for 6 h. In addition, six groups of samples were prepared using three different concentrations of InPc (0.3 wt.%, 0.5 wt.%, and 0.7 wt.% relative to the total mass of the mixture) and two different polymerization temperatures (75 ℃ and 80 ℃).

Preparation of Solid Transparent PMOL
Cross-linked P(MMA-co-DMAEA)-PEGMA OL microsphere powder was obtained through a freeze-drying process, 20 mg of which was evenly spread on the gasket in a round mold cavity (the diameter is 20 mm). After that, the mold was heated to 130 °C and preserved for 10 min to make sure that the powder was heated evenly. The PMOL were thermo-compressed at 10 MPa for 10 min. The heating and cooling rates was 5 °C/min. Before the compression process, a mold releasing agent was smeared on the formed surface of the mold to prevent the device from adhering to the mold. Finally, the solid transparent PMOL was obtained (20 μm in thickness, Supplementary Fig. 3).

Characterizations
Microstructures were recorded with a scanning electron microscope (Talos F200X, TFS Ltd., USA) and transmission electron microscopy (MAGNA, TESCAN Ltd., Czechia). For cross-sectional observation, the solid transparent PMOL were fractured while being submerged in liquid nitrogen. UV absorption of the PMOL and reflectivity spectra of the devices were acquired by using a UV-visible spectrometer (SolidSpec-3700, Shimadzu, Japan). The third-order NLO properties of the PMOL were evaluated vis the Z-scan technique with an Nd:YAG laser as the excitation light source (wavelength: 532 nm, pulse width: 8 ns). The dynamic behavior of the PMOL was measured using a femtosecond transient absorption (fs-TA) spectrometer (Helios, Ultrafast Systems, USA) under an excitation wavelength of 625 nm and a monitoring wavelength of 430-780 nm. Additionally, nanosecond transient absorption (ns-TA) measurements were performed under an excitation wavelength of 380 nm and a monitoring wavelength of 420-750 nm. To eliminate static noise, a background subtraction was applied using spectra acquired prior to time-zero. Furthermore, to compensate for the group velocity dispersion of the white-light continuum probe, a chirp correction was implemented. Mechanical strength was characterized via a Nano indenter G200 (MTS, USA) with a diamond indenter with a Berkovich geometry. Thermal stability of the nanosphere powder was measured by thermogravimetric analysis (TGA8000, PerkinElmer Instruments, USA). DSC was performed using a thermal analyzer (DSC 2500, TA Instruments, USA). FT-IR characterization and Raman spectra characterization of the structure of the PMOL were obtained by a Nicolet iS50R (Thermo Scientific, USA) using ATR mode and SENTERRA II (Bruker Optics, Germany), respectively. The nanometer indentation points were recorded with an AFM (Ntegra PRIMA, NT MDT Ltd., Russia). Sample pictures were taken at room temperature (Sony a7r3, Sony, Japan). The laser protection performance of the material was measured by a 532-nm laser (400 mW, HongDu Electronics), a smartphone (OPPOA72, OPPO, China) and CCD chips (ICX633BKA, Shenzhen Chuangsheng Weiye Technology Co., Ltd., China). The images of the microlens layer of the CCD chips were obtained using an optical microscope (LV150N, Nikon, Japan). An infrared thermal imager was used to record the heating effect after laser irradiation (DS-2TPH10−3AUF, HIKVISION, China).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Comments\nIndium phthalocyanine (InPc) encapsulated into polymer microspheres at 0.3, 0.5 and 0.7 Wt.% outsmarts pristine InPc in\nthe photophysical properties. Polymer incorporations prompt amino and hydroxyl derivatives near the co-ordination sites\nfosters as electron rich sites. Initially InPc ascribes to a five-level energy structure, hence the composite structure reduces\nthe intersystem crossing barrier enhances the reverse saturable absorption. The increase in nonlinear optical absorption\naugmented by DFT calculation and transient absorptions spectroscopy. This research work looks interesting and well\norganized however the author needs to address the following comments\n1. How does the performance compare to that of previously reported materials used as optical limiters? In addition to the\ncomparison with Pcs-based materials, it would be helpful to include performance comparisons with other classes of\nmaterials as well.\n2. From the TEM image Fig. 2e the encircled particles are represented as phthalocyanines (PCs) how the author confirms it\nas PCs?\n3. In Fig. 2g analyzing the glass transition temperature of the samples where 0.5 Wt.% shows higher when compared with\n0.7 Wt.%, explain the reasons behind the incremental result?\n4. In FT-IR spectra 200-5 samples (0.5 Wt.%) show the intense and broadest transmittance than all samples? the reasons to\nbe included in the manuscript\n5. In Fig. 3b XPS spectra analysis for microspheres and PMOL samples there is a clear peak shift in In 3d spectra,\nhighlighting the peak shift with plausible reason and include in the manuscript.\n6. Exploring the intensity dependent nonlinear optical absorption would be more suitable to show the low intensity excitation\nyielding high transmittance saturable absorption (SA) effects for prominent optical limiter.\n7. How do you confirm that low transmittance dip ascribed to nonlinear absorption (RSA) effects where scattering also might\naffect the light matter interaction. The author should verify that peak is solely due to nonlinear absorption and include in the\nmanuscript.\n8. Inorganic metal oxides synthesized by facile wet chemical techniques show good physical and thermal stability also\nyields better third-order nonlinear absorption. The author should explain how organic indium phthalocyanines are better than\ninorganic metal oxides.\n9. What happens to the nonlinear absorption by further increasing the wt.% addition to 0.9 Wt.% or explain the reasons why\nthe incorporations stopped at 0.7 Wt.% addition.", "reviewer_2": "The authors present a novel and well-executed approach to addressing the persistent challenges of aggregation and\nphotodegradation in solid-state organic optical limiters (OLs). The proposed strategy of anchoring indium phthalocyanine\n(InPc) within polymer microspheres via coordination bonds, followed by thermo-compression into a robust solid device, is\ninnovative. The reported nonlinear optical performance is impressive and is convincingly supported by a comprehensive set\nof characterizations, including DFT calculations, transient absorption spectroscopy (TAS), and practical application tests. This study is timely and holds significant potential for the field of laser protection. I recommend publication after the authors\naddress the following points to further enhance the manuscript's clarity, depth, and impact.\n1. The fabrication process of the PMOL is well described, but the manuscript would benefit from more detailed information\nabout the synthesis conditions. For example, it would be helpful to specify the exact temperatures and times used for the\nhigh-elastic-state thermo-compression process, as these factors could significantly influence the final properties of the\nPMOL. Providing such details will help readers replicate the procedure and better understand the conditions that contribute\nto the material's performance.\n2. While the manuscript is well-written, a few minor language issues and typographical errors remain:\nAbstract, line 17: \"The key innovation lays in...\" should be \"lies in...\"\nAbstract, line 26: \"This work provided presenting a viable strategy...\" is grammatically awkward. I suggest revising it to: \"This\nwork presents a viable strategy...\" or \"This work provides a viable strategy...\"\nIntroduction, line 39: \"were motivated to design to be\" is a bit clunky. I recommend: \"are designed to be...\"\nI recommend performing a thorough proofread to address similar minor grammatical issues throughout the manuscript.\n3. Some recent studies on third-order optical limiting should be cited to provide a more comprehensive background. I\nsuggest including the following references: 10.1002/cjoc.70314 and 10.1002/cjoc.202400423.\n4. The authors propose a coordination-bond anchoring strategy for InPc, which is supported by promising DFT calculations.\nHowever, further discussion is needed on how the coordination bonding specifically affects the electronic properties of InPc\nand the intersystem crossing (ISC) mechanism. The manuscript would benefit from a more detailed explanation of how these\nfindings translate into enhanced optical limiting performance. Additionally, it would be helpful to include a comparison with\nother known strategies for improving the performance of optical limiters, providing broader context and situating the\nproposed strategy within existing literature.", "reviewer_3": "In the submitted manuscript, the authors present a novel all-solid, passive optical limiter integrating indium phthalocyanine\nanchored to functional moieties within polymer microspheres. The system is investigated using both DFT theoretical\ncalculations and experimental spectroscopic techniques. At first glance, the manuscript appears well-written and contains a\nnumber of nicely prepared figures. However, a more detailed evaluation reveals that the current scientific depth and rigor do\nnot seem sufficient for Nature Communications.\nBelow, I list specific issues and inaccuracies identified during the review. All of these points must be addressed and\ncorrected (or clearly justified) by the authors:\nPage 7, Figure 2 (h) and (i) — These datasets represent FT-IR and Raman spectra and should be labeled accordingly,\nrather than being referred to as “curves” in the caption. These are \"spectra\", not \"curves\".\nPage 10, Figure 3 (g) — The traces shown are transient absorption (TA) spectra recorded at different delay times after the\nexcitation pulse, not “different time scales” as stated.\nInterpretation of TAS results (Page 11, lines 238–250) — I strongly disagree with the interpretation provided. As an expert in\ntime-resolved spectroscopy, I believe the data clearly indicate a sub-nanosecond transient — likely an excited singlet state\n(S1→Sn transition) — with a lifetime of approximately 300 ps. This lifetime could reasonably reflect the rate of intersystem\ncrossing to the triplet state (k ≈ 3 × 10¹⁰ s⁻¹). Moreover, because the TA signal does not return to zero, it is evident that the\ntriplet state persists for a much longer duration (microseconds or even milliseconds). Such long-lived dynamics cannot be\ncaptured within the ∼3 ns time window of the experimental setup. Therefore, the interpretation given in lines 248–249 is\nincorrect or, at best, insufficiently supported.\nUltrafast lifetime of 28.78 ps — This should be significantly rounded (e.g., to ~29 ps), as the time resolution of the setup is\nvery unlikely to justify two-decimal precision. Additionally, this lifetime appears to arise from a purely mathematical global-\nfitting procedure and may lack clear physical significance. The authors should investigate whether a single-exponential\ndecay with an offset provides an equally valid description. It is also essential to state whether a chirp correction was applied.\nThe experimental configuration must be described in greater detail, as these results are central to the discussion of excited-\nstate dynamics.\nPage 13, line 353 — 532 nm refers to a wavelength, not a wavenumber, and should be corrected accordingly.\nAbsorbance spectra labeling — The notation “OD” on the y-axis should be removed. Absorbance is dimensionless; labeling\nit with a “unit” could be misleading.\nIn summary, although the work may hold potential for publication in a more specialized journal, it requires substantial\nrevision before being considered suitable for publication. Therefore, I recommend MAJOR REVISION."}, "author_response": "Dear editor and reviewers ,\nThank you for your kind attention and considering our work in “All-solid passive organic limiter\nvia coordination-bond anchoring strategy”. We appreciate you and the reviewers for your helpful\ncomments and valuable suggestions. According to the comments for three reviewers, we have made\nthe following revisions: added intensity-dependent nonlinear absorption experiments, provided finer\ndetails of the synthesis to ensure the reproducibility of our results, discussed the influence of\ncoordination bonding on the InPc electronic properties, modified the interpretation of time-resolved\ndata, and included more details on the experimental setup. Our point-by-point responses are\nprovided below.\n[... Author responses to Reviewers 1, 2, and 3 ...]"}, {"round": 2, "reviewer_comments": {"reviewer_1": "I would like to thank the authors for their thorough and well-organized revision. The comprehensive rebuttal and the\nmodifications made to the manuscript—particularly the addition of the intensity-dependent nonlinear absorption experiments,\nthe deepened DFT analysis of the coordination bonds, and the refined interpretation of the time-resolved data—have fully\nresolved my previous concerns.\nThe 'all-solid passive organic optical limiter via coordination-bond anchoring strategy' presented in this work is scientifically\nsound and demonstrates significant potential for practical laser protection applications. The revisions have substantially\nelevated the quality of the manuscript. I have no further questions or requests for revision. Congratulations on a fine piece of\nwork.", "reviewer_2": "The article has been revised very carefully, and I recommend accepting it."}, "author_response": "Dear editor and reviewers ,\nThank you for the positive decision and for guiding our manuscript toward publication. We have\ncarefully addressed all editorial requests, including meticulous formatting, figure corrections, and\nthe submission of editable source files, data, the Change of Authorship Request Form, and the\nupdated Competing Interests Statement, as detailed in the Author Checklist and Cover Letter.\n[... Author responses to Reviewers 1 and 2 ...]"}]

Decision letter