Introduction

Light-driven dynamic self-assembly systems with spatiotemporally tunable luminescence have emerged as a frontier in adaptive materials science1, owing to their transformative potential in photonic devices2,3, biomedical imaging4,5, drug delivery6,7,8, encrypted information storage9, and intelligent sensing platforms10. The non-invasive nature and spatiotemporal precision of photonic regulation, as evidenced by recent advances in supramolecular engineering, provide an ideal mechanism for remote manipulation of emissive properties without compromising material integrity11. Nevertheless, achieving spatiotemporal control of supramolecular self-assemblies over multichromatic fluorescence emission in self-sustaining systems remains fundamentally challenging, particularly in reconciling three critical aspects: (1) molecular-scale stereoconfigurational switching fidelity, (2) nanoscale morphological programmability, and (3) closed-loop reconfigurability with post-processing resilience.

Current strategies employing organic photoswitches, including spiropyrans12, azobenzenes13,14, diarylethenes15,16, spirooxazine17, and stilbenes18, exploit light-induced conformational changes to modulate fluorescence through π-conjugation alterations19,20. Notable advancements include amphiphilic merocyanine-based dissipative systems, where visible-light-driven spiropyran-merocyanine interconversion enables transient nanoparticle assembly with chitosan, exhibiting tunable lifetimes from minutes to hours21,22,23,24. Subsequent integration with polyethylenimine further allows morphological diversification of these nanostructures25. However, these systems crucially depend on exogenous fluorescent dyes to achieve time-dependent chromatic variations, inherently lacking intrinsic fluorescence responsivity26. Moreover, their reliance on non-renewable polymer matrices significantly limits sustainability and practical applicability.

Contemporary approaches to phototunable multichromatic systems predominantly utilize extrinsic chromophore incorporation or static covalent architectures27, inherently constrained to transitions between predetermined equilibrium states. While single-fluorophore systems theoretically promise simplified spatiotemporal control, their practical implementation faces dual challenges: achieving spectrally pure emission across broad visible wavelengths, and maintaining robust reversibility in solid-state matrices28. Pioneering work on π-extended spiropyran derivatives has demonstrated exceptional photochromic breadth (Δλ > 200 nm) through intramolecular charge transfer modulation, attaining 95% photoisomerization yield29. Nevertheless, such molecular designs encounter intrinsic limitations including solvent-dependent performance degradation and laborious synthetic protocols, particularly when transitioning from solution-phase to solid-state applications29,30.

In contrast, supramolecular engineering strategies leveraging programmable host-guest interactions present avenues for achieving spatiotemporally resolved fluorescence modulation31,32,33,34,35. Representative systems employ π-π stacking modulation in pyrene-acylhydrazine conjugates, where γ-cyclodextrin-mediated encapsulation enables spectral shifting from blue to yellow emission28. More recently, cucurbit[8]uril-mediated co-assembly of spiropyran-functionalized cyanostilbene copolymers has achieved visible-light-driven reversible transitions between blue and orange states, coupled with 2D-to-1D morphological switching36. These systems fundamentally rely on external chemical stimuli (e.g., enzymatic inputs) or continuous energy dissipation, exhibiting their potential autonomy in creating transient optical states. However, the absence of hierarchical structural control across molecular-to-macroscopic scales hinders the development of integrated photonic platforms.

The integration of spatiotemporally programmable fluorescent self-assemblies into autonomous macroscopic substrates represents a critical step toward practical applications, yet confronts persistent challenges in preserving dynamic reconfigurability while ensuring mechanical integrity37. While hydrogel38,39, polymeric film40,41,42,43, and membrane- based44 platforms have demonstrated partial success, cellulosic paper emerges as a superior substrate due to its unique combination of sustainability45, structural robustness, and facile processibility46,47. Conventional photochromic materials fabrication, however, remains constrained by covalent fixation strategies that inherently sacrifice recyclability and temporal control precision. For instance, UV-polymerized spiropyran-embedded hydrogels require specialized patterning equipment and exhibit gradual photobleaching48. Similarly, covalent grafting of diarylethenes onto cellulose via thiol-X coupling achieves only irreversible monochromatic switching, necessitating complex dye blending for multicolor displays49.

To transcend these limitations, we design and construct a visible-light-responsive supramolecular system based on protonated vinylpyridinium-derived merocyanine (VPMEH) and cucurbituril macrocycles (Fig. 1). This non-covalent design enables three synergistic functionalities, including time-programmable fluorochromism between orange and green through host-guest stoichiometric modulation, morphology-dependent emission enhancement, and spontaneous thermal recovery without external energy input. The VPMEH-cucurbituril systems maintain >95% emission intensity retention over 5 light irradiation-thermal relaxation cycles. When coupled with cellulose nanofibrils through multivalent hydrogen bonding, the system achieves multi-state color switching on free-standing paper substrates. Moreover, the self-assembly and paper fabrication processes are entirely driven by non-covalent interactions, which not only enables multiple reuse cycles but also ensures portable and foldable processibility. Crucially, our light-fueled dissipative assembly operates through autonomous energy dissipation pathways, fundamentally differing from previous equilibrium-bound systems. This paradigm not only establishes a blueprint for reprocessable cellulosic-based photonic materials but also unlocks opportunities in secure information architectures and biodegradable optoelectronics.

Fig. 1: The design strategy of photochromic fluorescent complexes loading on cellulosic paper.
Fig. 1: The design strategy of photochromic fluorescent complexes loading on cellulosic paper.
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a Chemical structures and schematic illustration of VPMEH and VPSP. b Photoreconfigurable illustration of VPMEH and their host-guest complexation with cucurbiturils. c Schematic illustration of photoconfigurable and reprocessable cellulosic paper.

Results

Phototransformation behavior and host-guest complexation with cucurbiturils

The organic photochromic molecule, VPMEH, was designed and synthesized through a four-step procedure (Supplementary Fig. 1) and characterized by 1H-NMR,13C-NMR, and high-resolution mass spectra (Supplementary Methods and Supplementary Figs. 2–14). The two distinct states of the photoswitch, VPMEH and VPSP, were identified and analyzed by 1H-NMR (Supplementary Figs. 15–18). The spiropyran form of VPSP was obtained after irradiating 475 nm light from merocyanine form of VPMEH. Subsequently, the stereoscopic spiro-crossed VPSP reverted to the planar VPMEH structure through thermal relaxation in the dark (Fig. 2a). Specifically, the phototransformation from VPMEH to VPSP was confirmed through 1H-NMR (Fig. 2b), whereby the shift of most protons to the upfield area was observed, accompanied by a change in the molecular skeleton from merocyanine to spiropyran (Supplementary Table 1). Notably, the coupling constants of protons Hi and Hj in VPMEH were measured as 16.2 Hz and 7.2 Hz, respectively. The larger coupling constant of 16.2 Hz can be unambiguously assigned to the trans-vicinal coupling (3Jtrans) between Hi and Hj across the C = C double bond, which is characteristic of a trans-alkene configuration, while the 7.2 Hz coupling arises from a long-range coupling along the conjugated system. Upon conversion to VPSP, these coupling constants changed significantly to 7.8 Hz (Hi) and 9.6 Hz (Hj). The disappearance of the 3Jtrans coupling and the convergence of the values to those typical of aliphatic ring systems clearly indicate that the original C = C double bond has been incorporated into the rigid spirocyclic structure during the phototransformation, rather than undergoing a simple trans-to-cis configurational change. Moreover, the N-methylene protons Hf experience a marked upfield shift from δ 4.84 to 2.39 ppm (Δδ = −2.45 ppm) upon conversion of VPMEH to VPSP, in agreement with previous reports on MCH⁺-type merocyanine photoacids and consistent with the formation of an indolinium species at the indoline nitrogen50,51.

Fig. 2: Structural characterizations of VPMEH and VPSP, and their complexes with cucurbiturils.
Fig. 2: Structural characterizations of VPMEH and VPSP, and their complexes with cucurbiturils.
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a Illustration with chemical structures and DFT-optimized geometries of VPMEH and VPSP optimized by Gaussian 16 in B3LYP/6-31 + G form. The schematic corresponds to the overall (global) process rather than any single elementary equilibrium. The equilibrium is divided into three parts: VPSP ⇌ cis-VPME (isomerization), cis-VPME ⇌ cis-VPMEH (protonation/deprotonation), followed by cis-VPMEH ⇌ trans-VPMEH. 1H-NMR spectra of VPMEH (b) and VPSP (c) in DMSO-d6 at 298 K. UV-Vis absorbance spectra of VPMEH, VPSP and their complexes with cucurbiturils in aqueous solution (d) (inset: digital photographs of 1 = VPMEH, 2 = VPSP), and their changing cycles at 460 nm (e). (VPMEHinitial = 0.10 mM, [CB[7]] = 0.10 mM, [CB[8]] = 0.05 mM) f MALDI-TOF mass spectra of the complexes of VPMEH/VPSP and cucurbiturils.

UV-Vis absorption spectra (Fig. 2c) demonstrated that VPMEH exhibited a maximum absorbance at 460 nm in aqueous solution, while VPSP showed a maximum absorbance at 390 nm, accompanied by a visible color change from orange to pale yellow. The reversible conversion between VPMEH and VPSP showed excellent fatigue resistance, sustaining at least 10 cycles without significant degradation (Fig. 2d and Supplementary Fig. 19). The conversion extent was calculated to be above 95% based on the standard curve derived from absorption spectra (Supplementary Fig. 20) and reported literature24. Time-dependent kinetic studies revealed that aqueous VPMEH quantitatively converted to VPSP under 475 nm light irradiation within 20 s. VPSP then thermally relaxed back to VPMEH form in the dark for 10 min at 298 K (Supplementary Fig. 21). These dynamic processes were found to be temperature-dependent, with slower relaxation observed at lower temperatures (Supplementary Fig. 22). The pH of a 0.10 mM aqueous solution of VPMEH decreased from 5.37 to 4.34 under 475 nm irradiation and returned back in the dark (Supplementary Fig. 23). The VPMEH/VPSP transformation remained effective across a wide range of initial pH 1–7 despite proton transfer relying on the initial pH (Supplementary Fig. 24). Additionally, it works well in various solvents (Supplementary Fig. 25).

We expect that VPMEH will serve as a promising guest molecule for molecular recognition within typical host macrocycles, such as cucurbiturils. Therefore, we have chosen cucurbit[7]uril (CB[7]) and cucurbit[8]uril (CB[8]) as examples to study their potential dynamic host-guest binding behavior with VPMEH. UV-Vis absorption spectra (Fig. 2d) showed a slight redshift upon adding CB[7]/CB[8] to 0.10 mM aqueous solution of VPMEH, suggesting enhanced interactions between cationic pyridinium moiety of VPMEH and cucurbiturils. These interactions are likely driven by π-π stacking, ion-dipole forces, and van der Waals forces. Job’s plots from UV-Vis absorption spectra were constructed to determine the host/guest binding stoichiometry. The binding ratios of VPMEH-CB[7] and VPSP-CB[7] complexes were both 1:1 (Supplementary Figs. 26 and 27). Upon adding CB[7] to 0.10 mM aqueous VPMEH, with or without irradiation, clear isosbestic points emerged, signifying the establishment of equilibrium with 1.0 equivalent of CB[7]. The binding constants were determined to be (4.66 ± 0.24) × 104 and (4.01 ± 0.08) × 104 M–1, respectively (Supplementary Figs. 28 and 29). Interestingly, the binding ratio of VPMEH-CB[8] was found to be 2:1 whereas VPSP-CB[8] maintained a 1:1 binding ratio (Supplementary Figs. 30 and 31). The binding constants for VPMEH-CB[8] were further quantified as (0.69 ± 1.23) × 106 for K1 and (3.17 ± 3.83) × 105 M−1 for K2, respectively, which are significantly larger than the binding constant of VPSP-CB[8], (2.79 ± 0.11) × 104 (Supplementary Figs. 32 and 33).

To confirm the binding stoichiometries, MALDI-TOF mass spectra (Fig. 2e) and 1H NMR titration experiments (Supplementary Figs. 34–37) were conducted. Upon CB[7]/CB[8] were added to 0.10 mM aqueous solution of VPMEH, characteristic peaks corresponding to Hr, Hi, Hm, Hj, Hd, Ha, Hb, and Hl exhibited field shifts, indicating the inclusion of VPMEH within the cavities of CB[7] and CB[8] (Fig. 3a, b). The chemical shifts stabilized upon reaching the expected binding ratios: 2:1 for VPMEH-CB[8] and 1:1 for VPMEH-CB[7], VPSP-CB[7], and VPSP-CB[8]. The variation in binding stoichiometries is attributed to the planar geometry of VPMEH and the influence of ion-dipole interactions. 1H-1H ROESY experiments between VPMEH and CB[7]/CB[8] are further shown Supplementary Figs. 38 and 39. According to density functional theory (DFT) calculations (Fig. 3c and Supplementary Fig. 40), geometry optimization revealed that both 1:1 and 2:1 complexes of VPMEH and CB[8] are feasible structures. The 2:1 VPMEH-CB[8] complex has the lowest Gibbs free energy (ΔG = –118.15 kcal mol–1), much lower than that of the 1:1 complex (ΔG = –16.99 kcal mol–1), indicating its higher thermodynamic stability. In the 2:1 complex, the CB[8] molecule encapsulates two VPMEH molecules in a head-to-tail manner. The sulfonate indole group of VPMEH acts as a capping group, forming multiple hydrogen bonds with the carbonyl oxygen at the CB[8] portal, further stabilizing the complex. Under 475 nm irradiation, the formation of the stereoscopic spiro-crossed structure in VPSP molecules alters the host-guest interaction mode. The steric hindrance of the spiro-crossed structure disrupts the 2:1 complex, ejecting one guest molecule from the CB[8] cavity and forming a less stable 1:1 complex (ΔG = –58.18 kcal mol–1). By comparing Gibbs free energy changes during the photoinduced process, the intermediate VPMEH-INT tends to form a 1:1 complex with CB[8] (ΔG = –88.94 kcal mol–1), identified as a key transition state in the photoinduced transformation.

Fig. 3: Proposed mechanisms of host-guest complexation and light-driven configurational change of VPMEH and CB[8] complex.
Fig. 3: Proposed mechanisms of host-guest complexation and light-driven configurational change of VPMEH and CB[8] complex.
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a Partial 1H-NMR spectra (in DMSO-d6) of VPMEH (upper) and VPMEH-CB[7] (lower). b Partial 1H-NMR spectra (in DMSO-d6) of VPMEH (upper) and VPMEH-CB[8] (lower). c Gibbs free energy profile and schematic representation of the host–guest complexes of VPMEH/VPSP/VPMEH-INT with CB[8] obtained and optimized by Gaussian 16, B3LYP/6-31 + G form.

Kinetics and reversibility of supramolecular self-assemblies

We then investigated the irradiation kinetics of VPMEH-CB[7] and VPMEH-CB[8] under 475 nm light irradiation, and the thermal relaxation kinetics of VPSP-CB[7] and VPSP-CB[8] in the dark, revealing excellent reversibility within 10 cycles (Supplementary Figs. 41 and 42). Both VPMEH-CB[7] and VPMEH-CB[8] transformed into VPSP-CB[7]/VPSP-CB[8] in 40 s under 475 nm light irradiation and relaxed back in 12 min at 298 K in the dark (Supplementary Figs. 43 and 44). The half-lives of the thermal relaxation processes from VPSP-cucurbituril complexes (187 s for CB[7] and 138 s for CB[8]) to their VPMEH forms are calculated to be longer than that of VPSP (105 s), indicating the stabilization effect of cucurbiturils on the VPSP form based on macrocyclic confinement (Supplementary Fig. 45). The pH of VPMEH-CB[7] decreased from 5.22 to 4.50 during the VPMEH-to-VPSP transformation and returned back after thermal relaxation (Supplementary Fig. 46). Similarly, VPMEH-CB[8]/VPSP-CB[8] showed reversible pH changes between 5.15 and 4.43 (Supplementary Fig. 47). The VPMEH/VPSP transformation for the complexes remained effective across a wide range of initial pH 1–7 (Supplementary Figs. 46c and 47c).

Time-dependent fluorochromism of supramolecular assemblies

VPMEH, VPSP, and their host-guest complexes with cucurbiturils were found to exhibit tunable fluorescence properties. DFT calculations of frontier molecular orbitals elucidated the fluorochromism mechanism (Supplementary Fig. 48). For VPMEH, intramolecular charge transfer was observed between the pyridinium and indole groups. A larger HOMO-LUMO gap resulted in higher energy release upon relaxation to the ground state, corresponding to the emission of photons with shorter wavelengths. As a result, the fluorescence spectrum of VPSP exhibited a blue shift compared to that of VPMEH. Fluorescence spectra revealed that VPMEH exhibited orange fluorescence (λmax = 560 nm), while VPSP showed weak green fluorescence (λmax = 510 nm) in aqueous solution due to its extended conjugation and intramolecular charge transfer from the pyridinium moiety (Fig. 4a). Concentration-dependent fluorescence studies can rule out interference, such as inner-filter effects or aggregation-caused quenching, at a concentration of 0.1 mM (Supplementary Fig. 49). The fluorescence of VPMEH/VPSP during phototransformation and thermal relaxation demonstrated excellent reversibility within 5 cycles (Supplementary Fig. 50a–b). The maximum emission at 560 nm decreased by 72% after 30 s of 475 nm irradiation, accompanied by a blue shift, and spontaneously recovered in the dark (Supplementary Fig. 50c–f, Supplementary Movies 1 and 2). Fluorescence titration experiments showed that the 560 nm emission of VPMEH-CB[7] increased by 3-fold as CB[7] were added to 0.10 mM VPMEH as emission color slightly turned to bright yellow. The fluorescence emission spectra predominantly stabilized when the VPMEH and CB[7] molar ratio exceeded 1:1, confirming the 1:1 complexation ratio (Supplementary Fig. 51). The fluorescence intensity of VPMEH-CB[7] decreased after 30 s of 475 nm irradiation with the emission color changing from bright yellow to green (Fig. 4b and Supplementary Movie 3), and recovered in the dark (Fig. 4c, Supplementary Fig. 52 and Supplementary Movie 4). The luminescence behavior was highly reversible for up to 5 cycles (Supplementary Fig. 53).

Fig. 4: Dissipative kinetics and time-dependent fluorescence characterizations of VPMEH-cucurbituril self-assemblies at 298 K.
Fig. 4: Dissipative kinetics and time-dependent fluorescence characterizations of VPMEH-cucurbituril self-assemblies at 298 K.
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a Fluorescence spectra of VPMEH, VPSP, and their complexes with cucurbiturils. b CIE 1931 images of VPMEH-CB[7] under 475 nm irradiation from 0 to 30 s and the corresponding fluorescence photographs. c Fluorescence intensity changes at 490 nm and 560 nm of VPMEH-CB[7] in aqueous solution after 40 s of irradiation under 475 nm light and kept in the dark for 420 s. d Changing cycles of fluorescence intensity at 560 nm of VPMEH and VPMEH-CB[7] in aqueous solution after 40 s of irradiation under 475 nm light and kept in the dark for 420 s. e The half-lives for the thermal relaxation processes from VPSP and their complexes with cucurbiturils to their VPMEH forms obtained from UV-Vis absorption and fluorescence kinetics with cubic error bars. n = 3 independent experiments, with the bar data indicating mean ± SD. f Confocal images of the dynamic conversion between VPMEH-CB[7] and VPSP-CB[7] in different wavelength emission channels (Channel 1 with i and ii: 400–500 nm; Channel 2 with iii and iv: 500–600 nm). The scale bar is 20 μm. ([VPMEH]initial = 0.10 mM, [CB[7]] = 0.10 mM, λex = 365 nm).

A slight fluorescence enhancement and red-shift were observed for the VPMEH-CB[8] complex upon the addition of CB[8] to a 0.10 mM VPMEH solution, with its emission color remaining orange (Supplementary Fig. 54) The fluorescence kinetics of VPMEH-CB[8] was similar with that of VPMEH-CB[7] with good reversibility (Fig. 4d, Supplementary Fig. 55–56, Supplementary Movies 5 and 6). Notably, the fluorescence variation periods of thermal relaxation processes of VPSP-cucurbituril complexes appears shorter than those in UV-Vis absorption variation, which indicates that time-evolving fluorochromism of these dissipative self-assemblies relies on transformation of both conjugated molecular structure and aggregation state (Fig. 4e). Additionally, VPMEH-cucurbituril complexes all have similar fluorescence lifetimes around 1.5 ns (Supplementary Fig. 57).

Light-driven morphological reconfiguration of supramolecular assemblies

Since the host-guest complexation and the space confinement effect led to the time-dependent fluorochromism, we further investigated the morphological change of light-driven transformable dissipative self-assemblies formed by VPMEH-cucurbituril complexes via hydrophobic and electrostatic interactions. The changes of the dissipative self-assemblies were observed through time-dependent confocal images under fluorescent field, which exhibited consistent dynamic fluorescence behaviors (Fig. 4f). Furthermore, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) revealed that VPMEH-CB[7] (Fig. 5a, e) and VPMEH-CB[8] (Fig. 5c, g) can self-assemble into cuboid nanoparticles while VPSP-CB[7] (Fig. 5b, f) and VPSP-CB[8] (Fig. 5d,h) collapsed into larger spherical nanoparticles upon 475 nm light irradiation. Dynamic light scattering (DLS) data displayed the average diameters of 249 nm and 550 nm for VPMEH-CB[7] and VPMEH-CB[8], and that of 348 nm and 717 nm for VPSP-CB[7] and VPSP-CB[8], respectively (Fig. 5i). These nanoparticles of VPMEH-CB[7] and VPMEH-CB[8] had positive zeta potential of +37.0 mV and +37.3 mV, indicating cationic characteristics. In contrast, the nanoparticles of VPSP-cucurbituril showed nearly natural zeta potential (+1.93 mV and +2.22 mV) (Fig. 5j). The rigid merocyanine moiety in VPMEH led to well-faceted cuboid nanoparticles, while the more flexible spiropyran in VPSP resulted in spherical nanoparticles. In a control experiment, DLS data of VPMEH and VPSP alone present much smaller hydration diameters without cucurbiturils, accompanied by consistent zeta potential change (Supplementary Fig. 58).

Fig. 5: Morphological characterizations of VPMEH-cucurbituril self-assemblies.
Fig. 5: Morphological characterizations of VPMEH-cucurbituril self-assemblies.
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TEM image of VPMEH-CB[7] (a), VPSP-CB[7] (b), VPMEH-CB[8] (c), VPSP-CB[8] (d). The scale bar is 500 nm. SEM image of VPMEH-CB[7] (e), VPSP-CB[7] (f), VPMEH-CB[8] (g), VPSP-CB[8] (h). The scale bar is 500 nm. i, j, DLS and Zeta potential of VPMEH-cucurbituril self-assemblies. ([VPMEH]initial = 0.1 mM, [CB[7]] = 0.1 mM, [CB[8]] = 0.05 mM).

Hierarchical integration into recyclable cellulosic emitter

Due to the reprocessable advantages of paper over other substrates, we have selected needle bleached kraft pulp (NBKP) paper as representative cellulosic paper to fabricate composite materials based on VPMEH-cucurbituril dissipative self-assemblies (Fig. 6a). We prepared NBKP-VPMEH, NBKP-VPMEH-CB[7], and NBKP-VPMEH-CB[8] composite cellulosic papers through conventional technology of handmade paper.(Fig. 6b). Because solid-state nature of NBKP paper restricts molecular motion, the macrocyclic cucurbiturils are necessary to assist the loading of VPMEH on the paper, thereby providing sufficient space for molecular phototransformation and dissipative self-assembly. Confocal images confirmed the presence of intense luminescence on the cellulose fibers, indicating successful immobilization of VPMEH-cucurbituril self-assemblies and retention of their fluorescence properties (Fig. 6c). VPMEH-CB[7] showed variation in fluorescence intensity, while VPMEH-CB[8] exhibited variation in emission color. VPMEH-cucurbituril dissipative self-assemblies appeared the different fluorochromism behavior of VPMEH-cucurbituril self-assemblies in cellulosic paper compared to those observed in solution, probably because these dissipative self-assemblies are in different microenvironments (Fig. 6b,c). Fourier transform infrared (FTIR) spectroscopy (Supplementary Discussion 1 and Supplementary Fig. 59) and UV-Vis absorption spectra (Supplementary Fig. 60) also showed the well-dispersion of VPMEH-cucurbituril self-assemblies onto the paper. SEM further exhibited changes in the surface morphology of the VPMEH- cucurbituril self-assemblies onto the paper (Fig. 6d and Supplementary Fig. 61). VPMEH-CB[8], with its 1:2 binding capacity, exhibited better potential on space-confinement effect than VPMEH-CB[7], which might promote aggregation-induced emission characteristics. The VPMEH-CB[8] self-assemblies loading on the paper demonstrated superior tunable fluorescence performance compared to their behavior in solution (Fig. 6e and Supplementary Fig. 62).

Fig. 6: Morphological characterizations of VPMEH-cucurbituril self-assemblies-loaded cellulosic paper.
Fig. 6: Morphological characterizations of VPMEH-cucurbituril self-assemblies-loaded cellulosic paper.
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a Schematic diagram illustrating the fabrication of cellulosic paper loaded with VPMEH-cucurbituril self-assemblies. b Fluorescence spectra of cellulosic paper loaded with VPMEH-CB[8] self-assemblies. c Photographs of the prepared paper under 365 nm irradiation are shown with a scale bar of 10 mm. d Confocal images of cellulosic paper loaded with VPMEH-cucurbituril self-assemblies. The scale bar is 100 μm. e SEM image of cellulosic paper loaded with VPMEH-cucurbituril self-assemblies. The loaded VPMEH-CB[8] self-assemblies are marked by red circles. The scale bar is 1 μm.

Finally, we displayed the visual pattern on the cellulosic paper that separately loading VPMEH-CB[7] and VPMEH-CB[8] (Fig. 7a). The NBKP-VPMEH-CB[7] complex initially exhibited a green color. Upon irradiation with 475 nm light through a mask, a non-fluorescent pattern of “SEU” appeared on the paper, corresponding to the photoconversion of VPMEH-CB[7] to VPSP-CB[7] (Fig. 7b). This pattern self-erased in the dark due to the thermal relaxation of VPSP-CB[7] back to VPMEH-CB[7]. Similarly, the NBKP-VPMEH-CB[8] complex initially displayed an orange color. Upon irradiation with 475 nm light through a mask, a green color pattern of “CCE” appeared on the paper, resulting from the transformation of VPMEH-CB[8] to VPSP-CB[8]. This pattern also self-erased in the dark through thermal relaxation. Moreover, the self-assembly and paper fabrication processes are entirely driven by non-covalent interactions, which not only enables multiple reuse cycles but also ensures portable and foldable processibility (Fig. 7c, d and Supplementary Fig. 63). Building on these findings, we developed an in situ optical anti-counterfeiting method utilizing VPMEH-cucurbituril self-assemblies. By immobilizing these dissipative self-assemblies onto paper, we achieved precise control over the fluorescence properties of the material, offering an effective strategy for advanced anti-counterfeiting applications.

Fig. 7: VPMEH-cucurbituril self-assemblies-loaded cellulosic paper and its application in anti-counterfeiting.
Fig. 7: VPMEH-cucurbituril self-assemblies-loaded cellulosic paper and its application in anti-counterfeiting.
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Schematic representation (a) and photographs (b) of patterns on cellulosic paper loaded with VPMEH-cucurbituril self-assemblies after irradiation under 475 nm light followed by exposure to darkness. The scale bar is 0.5 cm. Photographs of recycling patterns (c) and free-standing of handmade cellulosic paper (d). The scale bar is 2 cm.

Conclusions

We have developed a visible-light-responsive dissipative supramolecular self-assembly system based on VPMEH and macrocyclic cucurbiturils. This system exhibits temporally programmable multimodal fluorescence behavior in aqueous solution through alternating 475 nm irradiation and thermal relaxation, demonstrating quantitatively reversible fluorescence intensity modulation via host-guest interactions and tunable emission switching between orange and green with exceptional reversibility. When integrated into freestanding cellulosic paper, the system achieves dual-color fluorescence switching, enabling dynamic pattern encryption/decryption and spatiotemporal concealment. Notably, the entire self-assembly process is governed by non-covalent interactions, which not only ensures robust recyclability and multiple reusability but also maintains structural integrity during reconfiguration. This work establishes a photoreconfigurable fluorochromic platform that bridges dynamic molecular recognition with macroscopic optical functionality, offering sustainable solutions for advanced information encryption, multi-level anti-counterfeiting, and smart optoelectronic applications in cellulose-based intelligent materials.

Methods

Synthesis of 3-(2-((E)-4-((E)-2-(1-ethylpyridin-1-ium-4-yl)vinyl)-2-hydroxystyryl)-3,3-dimethyl-3H-indol-1-ium-1-yl)propane-1-sulfonate (VPMEH)

(E)-1-ethyl-4-(4-formyl-3-hydroxystyryl)pyridin-1-ium (125 mg, 37 mmol) and 3-(2,3,3-trimethyl-3H-indol-1-ium-1-yl)propane-1-sulfonate (100 mg, 36 mmol) were added into anhydrous ethanol (2 mL) in a single-necked round-bottomed flask equipped with reflux condenser tube. The mixture was allowed to reflux overnight. The red solid VPMEH (184 mg, 77%) was obtained by filtration, washed with cold diethyl ether, and dried in the vacuum overnight. The structure was determined by 1H-NMR, 13C-NMR, 2D 1H-1H NOESY, and high-resolution mass spectra (HRMS) (Supplementary Figs. 10–13). 1H-NMR (600 MHz, DMSO-d6): δ 11.34 (s, 1H), 9.02 (d, J = 6.0 Hz, 2H), 8.58(d, J = 16.2 Hz, 1H), 8.47(d, J = 8.4 Hz, 1H), 8.33 (d, J = 6.6 Hz, 2H), 8.03 (d, J = 7.2 Hz, 2H), 7.99 (m, 2H), 7.88 (d, J = 7.2 Hz, 1H), 7.63 (t, J = 7.2 Hz, 2H), 7.48 (d, J = 8.4 Hz, 1H), 7.28 (s, 1H), 4.84 (t, J = 7.8 Hz, 2H), 4.57 (q, J = 7.2 Hz, 2H), 2.67 (t, J = 6.6 Hz, 2H), 2.20 (m, 2H), t (s, 6H), 1.55 (t, J = 7.2 Hz, 3H). 13C NMR (151 MHz, DMSO-d6): δ 181.93, 159.59, 152.61, 147.65, 144.72, 144.08, 142.18, 141.42, 139.88, 130.74, 129.72, 129.67, 126.74, 124.90, 123.54, 123.51, 119.35, 116.93, 115.60, 112.81, 63.26, 55.93, 52.37, 47.76, 46.04, 26.86, 25.14, 16.67. ESI-HRMS: m/z calculated for m/z C30H33N2O4S+ [M−Br]+, 517.21555; found, 517.21442.

Preparation of cellulosic paper

The needle bleached kraft pulp (NBKP) paper was prepared according to conventional technology of handmade paper52,53. 102 g of dry NBKP board was soaked in deionized water for 12 h and then torn into small pieces. A variable-speed Wali refiner (IMT-VL02, China) was utilized to refine the pulp to a freeness of (55 ± 2) °SR. Subsequently, the refined pulp was dispersed in deionized water using a standard fiber disintegrator (IMT-SJ01, China) to obtain a pulp solution with a concentration of 0.5 wt%. Hand sheets were formed from the pulp solution with a basis weight (65 g m–2)54.

Appropriate amounts of VPMEH-cucurbituril complexes were prepared and completely dissolved in 200 mL of deionized water to prepare 1 mM ablto the prepared solution, and the mixture was continuously stirred at room temperature for 2 h in the dark. The resulting slurry was filtered under vacuum, and the filter cake was compressed to form VPMEH-cucurbituril self-assemblies-loaded NBKP paper. Finally, the paper was pressed and dried overnight in an oven at 60 °C. For comparison, pure NBKP paper was prepared using the same procedure, but without the addition of the VPMEH-cucurbituril complexes.

Reprocessing of cellulosic paper

Small pieces of pure NBKP and VPMEH-CB[8] self-assemblies-loaded NBKP paper were individually cut and soaked in water. The pulp was subsequently refined using a refiner. During the re-preparation of cellulosic paper, customized molds were incorporated into the filtration step to fabricate distinct patterns.

Light irradiation experiments

The visible light irradiation experiments (λ = 475 nm) were carried out using a photochemical reaction apparatus with a 500 W Hg lamp and CEL-HXF300 14 V 50 W xenon lamp with optical filter. The optical power density was 15 mW cm–2 unless otherwise mentioned.

Optical anti-counterfeiting experiments for NBKP-VPMEH-cucurbituril cellulosic papers

Cellulosic paper with VPMEH-CB[7] self-assemblies was masked using a “SEU” stencil and irradiated with 475 nm light for 2 min. Subsequently, the 475 nm light was turned off, and the paper was kept in the dark for 30 min. Afterward, another photograph was captured under 365 nm light. The same procedure was applied to the NBKP-VPMEH-CB[8] paper, with a stencil patterned with “CCE”. Due to the visible blue stray light of the 365 nm light source and the diffuse reflection on the paper surface, the masked region of the paper appeared background blue color instead of dark under 365 nm irradiation.

UV-Vis spectroscopy

UV-Vis absorption spectra were recorded in a quartz cell (light path 10 mm) on a Shimadzu UV-2600 spectrophotometer at room temperature unless otherwise noted. The solvent used in UV-Vis experiments were DI H2O.

Fluorescence spectroscopy

Fluorescence spectra were recorded in a conventional quartz cell (light path 10 mm) on a Shimadzu fluorescence spectrophotometer RF-6000 at room temperature unless noted. The excitation wavelength was 365 nm unless mentioned. The fluorescence lifetimes were recorded in a conventional quartz cell (light path 10 mm) on a Horiba PluoroLog 3.

SEM imaging

Scanning electron microscopy (SEM) were recorded on a FEI Inspect F50. For the preparation of VPMEH-CB[7] and VPMEH-CB[8] self-assemblies, the corresponding solutions were applied dropwise onto the surface of a single-side-polished silicon wafer and dried in the dark. The self-assemblies corresponding to VPSP-CB[7] and VPSP-CB[8] were obtained by drying corresponding VPMEH-CB[7] and VPMEH-CB[8] precursors under 475 nm light irradiation. ([VPMEH]initial = 0.10 mM, [CB[7]] = 0.10 mM, [CB[8]] = 0.05 mM).

TEM imaging

Transmission electron microscopy (TEM) was recorded on a Talos F200X. The testing point resolution was 0.25 nm, the resolution was 0.12 nm, and the testing voltage was 200 kV. The samples of VPMEH-CB[7] and VPMEH-CB[8] were prepared by dripping the corresponding water dispersion solution on the surface of copper grid coated with carbon film and standing in the dark to dry. The self-assembled nano-particles corresponding to VPSP-CB[7] and VPSP-CB[8] were obtained by transferring VPMEH-CB[7] and VPMEH-CB[8] precursors to the surface of copper grid covered with carbon film and drying under 475 nm light irradiation. ([VPMEH]initial = 0.10 mM, [CB[7]] = 0.10 mM, [CB[8]] = 0.05 mM).

Confocal laser scanning microscopy

Laser confocal images were recorded on a TCS SP8 STED 3X for monitoring the conversion between self-assembled VPMEH-CB[7] and VPSP-CB[7] over time. VPMEH-CB[7] solution ([VPMEH]initial = 0.10 mM, [CB[7]] = 0.10 mM) were dripped into a laser confocal dish and placed on the laser confocal microscope. The dynamic processes were collected by confocal scanning as time-series of images with emission channels of 400-500 nm and 500-600 nm. The dynamic processes of VPMEH-CB[7] to VPSP-CB[7] were collected with an interval of 5 s under 475 nm light irradiation, and the dynamic processes of VPSP-CB[7] to VPMEH-CB[7] were collected in the dark with an interval of 1 min. For monitoring the conversion between self-assembled VPMEH-CB[8] and VPSP-CB[8] on NBKP paper, 1 ×1 cm VPMEH-CB[8]-loaded cellulosic paper were placed on laser confocal microscope. The conversion processes were collected by confocal scanning images with emission channels of 400–500 nm and 500–600 nm.

Dynamic light scattering spectroscopy and zeta potential experiments

VPMEH-cucurbituril self-assemblies were investigated on a laser light scattering spectrometer (Brookhaven NanoBrook Omni) equipped with the Pt electrode at 298 K. The hydrodynamic diameter (Dh) was determined by DLS experiments.

NMR spectroscopy

1H and 13C NMR spectra were recorded on a Bruker 600 MHz spectrometer at room temperature and were analyzed through MestReNova.

ESI-HRMS experiments

ESI-HRMS were recorded on Thermo Scientific Q Exactive combined quadrupole Orbitrap Mass Spectrometer.

MALDI-TOF Mass Spectra experiments

MALDI-TOF MS were recorded on a Bruker UltrafleXtreme. Samples of VPMEH-CB[7] and VPMEH-CB[8] were prepared by drying in the dark. Samples of VPSP-CB[7] and VPSP-CB[8] were prepared by drying corresponding VPMEH-CB[7] and VPMEH-CB[8] precursors under 475 nm light irradiation55,56. ([VPMEH]initial = 0.10 mM, [CB[7]] = 0.10 mM, [CB[8]] = 0.05 mM).

Fourier transform infrared FTIR spectroscopy

FTIR spectra were recorded on DEEP-FTIR-2 (BJSCISTAR Ltd. Co).

Density-functional theory (DFT) calculation

All the DFT computations were performed using the Gaussian 16 Software Package57. The Def2SVP basis set58 was employed to expand the wave functions. For the electron-electron exchange and correlation interactions, the functional B3LYP59, a form of the hybrid functional, was used throughout. The vander-Waals interaction was described using the DFT-D3BJ method60 that proposed by Grimme.