Unlocking Multi-photoresponse in Phenothiazine Derivatives Through Photoinduced Radical and Keto-Enol Tautomerism

Open AccessCCS ChemistryCOMMUNICATIONS13 Aug 2024Unlocking Multi-photoresponse in Phenothiazine Derivatives Through Photoinduced Radical and Keto-Enol Tautomerism Duo Xu, Tao Wang, Shitai Liu, Guiqiang Pu, Jie Yang, Manman Fang, Xiaogang Liu and Zhen Li Duo Xu Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207 Department of Chemistry, National University of Singapore, Singapore 117543 , Tao Wang Department of Chemistry, National University of Singapore, Singapore 117543 , Shitai Liu Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207 Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore 117585 , Guiqiang Pu Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207 Department of Chemistry, National University of Singapore, Singapore 117543 , Jie Yang Institute of Molecular Aggregation Science, Tianjin University, Tianjin 300072 , Manman Fang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Institute of Molecular Aggregation Science, Tianjin University, Tianjin 300072 , Xiaogang Liu *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207 Department of Chemistry, National University of Singapore, Singapore 117543 and Zhen Li *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207 Institute of Molecular Aggregation Science, Tianjin University, Tianjin 300072 Hubei Key Lab on Organic and Polymeric Opto-Electronic Materials, Department of Chemistry, Wuhan University, Wuhan 430072 Cite this: CCS Chemistry. 2024;0:1–11https://doi.org/10.31635/ccschem.024.202404450 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Achieving photochromism, photodeformation, and photoinduced room-temperature phosphorescence (RTP) simultaneously in a single type of molecule-doped film is a complex and challenging task. Here, we introduce an efficient design strategy that utilizes dicarbonyl as a bridge linking between phenothiazine (PTZ) units, thereby enabling a synergistic multi-photoresponse upon photoactivation. Our study reveals that thin films of polyvinyl alcohol (PVA) doped with five PTZ derivatives (DPTZCn: n = 1–5) show photoactivated RTP. Notably, the DPTZC1 variant in PVA film uniquely undergoes photoactivated macroscopic deformation and displays enhanced photoluminescence efficiency compared to its PTZ counterparts (DPTZCn: n = 2–5) in PVA films. Further photophysical analysis indicates that the exceptional performance of DPTZC1 stems from the combined effects of keto-enol tautomerism and matrix rigidification, which also facilitate the generation of photoinduced radicals in DPTZC1 in the PVA film. We investigate the potential bionic applications of the versatile DPTZC1, providing insights into the design of intelligent, photodriven materials based on RTP. Download figure Download PowerPoint Introduction Photoresponsive properties such as photoinduced room-temperature phosphorescence (RTP), photodeformation, and photochromism, have been extensively studied for their potential in areas such as photodriven soft robotics and chemical sensors.1–15 However, integrating these properties within a single type of molecule-doped film remains a rarity, largely due to their different light irradiation response mechanisms. Achieving effective responsiveness requires a deep understanding of the material's microscopic structural changes and photoresponse mechanisms after irradiation. The concept of tautomerism, especially keto-enol tautomerism in dicarbonyl compounds, plays a pivotal role in this context.16,17 Introduced by Laar in 1886, tautomerism has found extensive applications across synthetic, biological chemistry to materials science, underpinning the development of drugs and advanced materials.18–24 For example, the enthalpic and polar properties provided by keto-enol tautomerism in β-diketone compounds enable substrate activation, facilitating reactions to proceed in good yields.25 Similarly, the construction of covalent organic frameworks with keto-enol tautomerism has demonstrated favorable properties, such as enhanced benzylamine adsorption.26 Phenothiazine (PTZ), a highly versatile organic compound, has been used in various fields, including medicine, in vivo imaging, and batteries, and more recently in optoelectronic materials.27–36 For example, Wang et al. achieved dual phosphorescence from phenoxazine- and PTZ-decorated naphthalene, which could be ascribed to two conformationally modulated T1 states.37 Another example by Gao et al. reported that PTZ derivatives can enhance RTP performance due to their quasi-axial and equatorial conformations in different states.38 Moreover, Chen et al. proposed that emission behavior of the triplet state in PTZ-benzophenone derivatives can be modulated through selecting specific geometries of the intramolecular charge transfer states.39 We reason that the combination of PTZ with keto-enol tautomerism might augment RTP and create a synergistic multi-photoresponse in new material systems. In this system, the PTZ units can effectively engage in charge transfer processes, while the keto-enol equilibrium modulates these processes (Scheme 1). This synergy allows for a material system with nuanced responsiveness, capable of reacting to multiple photoresponses such as changes in light, color, and mechanical force. Scheme 1 | Design strategy using dicarbonyl as a linker between two PTZ units and possible mechanism of multiphotoresponse. The small molecule DPTZC1 was uniformly doped into the PVA film and then excited with 365 nm UV. (i) After UV irradiation, enol structures are continuously formed, which exhibit macroscopic deformation. (ii) Radical cations are stabilized through keto-enol tautomerism. (iii) These radical cations can generate hole-electron pairs, possibly with a large number of triplet excitons forming upon their recombination, which offer another possibililty to produce the triplet excitons. PVA contributes to this process by forming numerous hydrogen bonds, which stabilize the triplet excitons. Download figure Download PowerPoint For a proof of concept, we introduced five PTZ derivatives (DPTZCn: n = 1–5), each consisting of two PTZ units connected by a dicarbonyl linker (see Supporting Information Scheme S1). These PTZ derivatives differ in the spacer between the PTZ units. Once doped into a polyvinyl alcohol (PVA) film, all five derivatives exhibited photoactivated RTP. Notably, DPTZC1 exhibited the highest photoluminescence (PL) quantum yield, which can be attributed to the keto-enol tautomerism in its β-diketone linker, accompanied with macroscopic deformation of the film. Moreover, in the DPTZC1-doped PVA film, photoinduced cationic radicals were detected, as evidenced by both electron paramagnetic resonance (EPR) signals and photochromic behavior. These multifunctional characteristics of DPTZC1 enable potential applications in anticounterfeiting and bionics. Experimental Methods General Unless otherwise specified, the reagents used in the experiments were purchased commercially and the purity was of analytical grade. All chemicals were purchased from Sigma Aldrich PTE. LTD. (Singapore) and were not subjected to additional purification. Chromatographically pure toluene was used after anhydrous and oxygen-free treatment with a solvent purification system (VSPS-5; Vigor Technologies (Suzhou) Co. Ltd., Suzhou, China). For all air-sensitive reactions, the Schlenk technique was used in a nitrogen atmosphere. Synthesis for DPTZCn (n = 1–5) PTZ derivatives DPTZCn (n = 1–5) were synthesized through a one-step acylation reaction (see Supporting Information Scheme S1). Synthesis for hybrids PVA solution (3 wt %): Stir PVA (300 mg) in dimethyl sulfoxide (DMSO) (10 g) in a 20 mL flask at room temperature for one night until completely dissolved. Polyethylene (PE) solution (3 wt %): Stir PE (300 mg) in toluene (10 g) in a 20 mL flask at 100 °C for 2 h until completely dissolved. Incorporation of DPTZC1 into PVA film (1:10): First, dissolve 6 mg of DPTZC1 in 2 mL of the 3 wt % PVA-DMSO solution (DPTZC1:PVA = 1:10). Next, apply the mixture dropwise onto a glass substrate. After application, peel the DPTZC1-incorporated PVA film off the glass substrate and allow it to dry. Incorporation of DPTZCn (n = 1–5) into PVA film (1:60): First, dissolve 1 mg of DPTZCn in 2 mL of the 3 wt % PVA-DMSO solution (DPTZCn:PVA = 1:60). Next, apply the mixture dropwise onto a glass substrate. After application, peel the DPTZCn in PVA film off the glass substrate and allow it to dry. Incorporation of DPTZC1 in PVA film (1:600): 1 mg of DPTZC1 was first dissolved in 20 mL of a 3 wt % PVA-DMSO solution (DPTZC1:PVA = 1:600), then the mixture was applied dropwise to the glass substrate, after which the DPTZC1 in PVA film was peeled off from the glass substrate and dried. Incorporation of DPTZC1 in PE film (1:60): 1 mg DPTZC1 was first dissolved in 2 mL of a 3 wt % PE-toluene solution (DPTZC1:PE = 1:60), then the mixture was applied dropwise to the glass substrate, after which the DPTZC1 in PE film was peeled off from the glass substrate and dried. Characterization 1H and 13C NMR spectra were recorded using a Bruker Advance spectrometer (Bruker Singapore Pte. Ltd., Singapore; 400 MHz for 1H, 101 MHz for 13C) in chloroform-d (CDCl3), DMSO-d6, and acetone-d6. 1H and 13C NMR spectra were referenced with respect to residual solvent peaks: (1H) chloroform-d, 7.26 ppm, (13C) chloroform-d, 77.16 ppm, (1H) dimethyl sulfoxide-d6, 2.50 ppm, (1H) acetone-d6, 2.05 ppm. High-performance liquid chromatography (HPLC) spectra were recorded with a Shimazu HPLC chromatograph (Shimadzu (Asia Pacific) Pte. Ltd., Singapore) using acetonitrile as solvent. High-resolution mass spectra (HRMS) were measured on an AmaZon X LC-MS (Bruker Singapore Pte. Ltd., Singapore) for electrospray ionization. Melting points were measured using a WRS-1C Melting Point Tester (HINOTEK GROUP LIMITED, Ningbo, China). Ultraviolet–visible (UV–vis) absorption spectra were acquired at room temperature using an Agilent Cary 5000 UV–vis–NIR spectrophotometer (Agilent Technologies Singapore (Sales) Pte. Ltd., Singapore). Luminescence spectra were recorded with an Edinburgh FLS1000 spectrofluorometer (Edinburgh Instruments Ltd., Livingston, United Kingdom). Time-dependent phosphorescence spectra and excitation duration-dependent RTP behavior were collected by a QE65 Pro (Ocean Optics Inc., Shanghai, China). Optical photographs of the samples were obtained using an iPhone 12. EPR spectra were recorded on a JEOL JES-FA200 spectrometer (JEOL Asia Pte. Ltd., Singapore). The sample preparation method is described in the General Synthetic Procedure for Hybrids section and the molar ratio of the samples used for testing is 1:60. In addition, the film samples are cut into pieces approximately 8 mm × 20 mm in size for testing. All ground state optimizations were carried out at the density functional theory (DFT) level with Gaussian 16 using the ωB97XD functional and the triplet zeta valence with polarization quality (TZVP) basis set. Vibrational frequency calculations were performed to ensure that the optimized geometries represent the local minima. Excited-state calculations were performed at the time-dependent DFT level using the same functional and basis set as for the ground state geometry optimization. Spin–orbit coupling matrix elements (x) were calculated based on the optimized geometry of the singlet excited state. Optimizations for the triplet excited state were conducted at the ωB97XD/TZVP level. The surface potential energy scan was conducted using the geometry of the optimized triple excited state. Molecular orbitals were visualized using GaussView 6.0. Spin–orbit coupling matrix elements between singlet and triplet excited states were calculated using the ORCA 5.0.3 program. Results and Discussion The molecular structures and purities of these compounds were confirmed by 1H and 13C NMR spectroscopy, HPLC, and HRMS (see Supporting Information Figures S1–S11). In addition, the homogeneous dispersion of DPTZCn derivatives in PVA films was determined by powder X-ray diffraction analysis (see Supporting Information Figure S12), and the molecular packing of DPTZCn (n = 1–5) crystals was examined by single crystal X-ray diffraction (see Supporting Information Table S1). The high thermal stabilities of these compounds were demonstrated through thermal gravity analysis, revealing decomposition temperatures (Td) for DPTZCn (n = 1–5) at 213, 273, 285, 295, and 283 °C, respectively (see Supporting Information Figure S13). The UV–vis absorption spectrum and steady PL spectrum of DPTZCn solution were also characterized (see Supporting Information Figures S14 and S15). We firstly investigated the photophysical properties of DPTZC1 and DPTZC2 in PVA films (molar ratio = 1:60). The steady-state PL spectrum of DPTZC1 in PVA films exhibits a structured emission profile with PL maxima at 450 and 520 nm, respectively (Figure 1a), with a recorded PL lifetime of 1.83 ns (see Supporting Information Figure S16). DPTZC2 in PVA films presents a different emission behavior, characterized by a single peak at 425 nm and an extensive emission tail (see Supporting Information Figure S17). Notably, no afterglow was observed for DPTZC1 and DPTZC2 in PVA films upon a short excitation duration using a 5 W UV torch. However, the emission color gradually evolved from blue to yellowish green as the excitation duration increased (Figure 1b,c), resulting in a detectable afterglow (see Supporting Information Figure S18). The RTP intensity of DPTZC1 in the PVA film gradually increased with UV irradiation time, reaching saturation at 3600 s (Figure 1d). This was accompanied by an RTP quantum yield of 4.91% and a phosphorescence lifetime of 23.96 ms (see Supporting Information Table S2). This RTP behavior was ascribed to interactions between triplet excitons and 3O2. Initially, triplet excitons are quenched by 3O2, leading to the occurrence of RTP after the complete consumption of 3O2 (Figure 1e).40 DPTZC2 shows weaker RTP efficiency (0.83%) and shorter lifetime (7.54 ms) compared to DPTZC1 (see Supporting Information Figure S16 and Table S2). DPTZCn (n = 3–5) in PVA films also exhibited photoactivated RTP in PVA films but with lower RTP efficiency compared to DPTZC1. Figure 1 | (a) Steady-state PL spectra of DPTZC1 in PVA films in air at 298 K (delay time: 0.02 s, integration time: 100 ms). (b) Schematic illustration of excitation duration-dependent RTP behavior. (c) Excitation duration-dependent RTP behavior (Inset: photographs showing the afterglow of DPTZC1 in PVA under UV irradiation in air at 298 K). (d) In-situ time-resolved PL spectra for DPTZC1 in PVA with different excitation durations for 1 s, 1 min, and 6 min in air at 298 K (integration time: 100 ms). (e) Schematic illustration of the mechanism of photoactivated RTP. Molar ratio of DPTZC1:PVA = 1:60. Download figure Download PowerPoint In the DPTZCn (n = 1–5) crystal series, the steady-state PL exhibits main emission bands in the range of 505–541 nm (see Supporting Information Figure S19). The corresponding lifetimes for these emissions are 5.10, 3.09, 3.57, 4.61, and 5.58 ns (see Supporting Information Figure S20 and Table S2). Additionally, these crystals exhibit a noticeable afterglow visible to the naked eye (see Supporting Information Figure S21), with RTP emissions detected in the range of 514–550 nm. The lifetimes of these RTP emissions are 24.19, 31.84, 35.20, 38.18, and 34.72 ms, respectively, under ambient conditions. To better understand the variations in RTP performance, we investigated the light absorption behavior of DPTZC1 and DPTZCn (n = 2–5) in PVA films (molar ratio = 1:60). Under UV irradiation at 365 nm for 1 min, the initially colorless PVA film containing DPTZC1 gradually turned light orange (Figure 2a), which correlates with enhanced absorption in the range of 510–700 nm (Figure 2b). This observation aligns with previous reports that PTZ turns light orange upon air oxidation, where oxygen acts as a oxidant to promote charge separation during the photooxidation of PTZ ( Supporting Information Figure S22).41,42 We speculate that the photochromism of DPTZC1 in the PVA film is likely due to the formation of UV-induced cationic radicals (DPTZC1+•), as evidenced by a similar absorption band in cationic radicals from PTZ derivatives.43 Figure 2 | (a) Photographs showing the photochromic behavior. (b) UV–vis absorption spectra, and (c) EPR spectra of the DPTZC1 in PVA film (molar ratio = 1:60) before and after 365 nm UV irradiation for 5 min at the ambient environment. (d) Schematic illustration of the process of radical generation. (e) The diketone geometry of DPTZC1 in the S0 state (left) and the keto-enol geometry of DPTZC1+• in the radical state (right) calculated in ethanol at the ωB97XD/TZVP level. Download figure Download PowerPoint To validate out hypothesis, we conducted EPR analysis. Before UV treatment, no EPR signal was detected. However, upon UV irradiation for one minute, a notable enhancement of the EPR signal was observed, ranging from 326 to 332 G (Figure 2c). This change was further corroborated by a distinct color change of the film. Contrarily, these effects were absent in the DPTZCn (n = 2–5) series (see Supporting Information Figure S23). In the case of DPTZC1, the generated radicals are stabilized through keto-enol tautomerism (Figure 2d), a mechanism not prevalent in the other four PTZ derivatives. We next performed theoretical calculations using the DFT at the ωB97XD/TZVP level. The molecular structure with the cationic radicals exhibits a more planar structure in the PTZ fraction compared to the neutral state. More specifically, the dihedral angle of the two PTZ subunits increases from 130.68/133.16° (DPTZC1) in the neutral molecule to 132.13/174.75° (DPTZC1+•) in the molecule containing the cationic radicals (Figure 2e). This suggests, as in previous studies, that planar conformations with extended π-conjugation are more favorable for radical stabilization.44–46 This stabilization explains the observed differences: DPTZCn (n = 2–5) compounds exhibit neither a color change nor an EPR signal after UV excitation. The enhanced stability of DPTZC1's radical cations would facilitate the hole-electron recombination, thereby providing more possible chance to generate triplet excitons. Consequently, the RTP performance of DPTZC1 in PVA film improves significantly, from nearly 0% before UV irradiation to 4.91% after 6 min of irradiation (see Supporting Information Table S2). In contrast, the radicals formed in the other four PTZ derivatives lack this keto-enol tautomerism stability and are quickly quenched, preventing the recombination of holes and electrons. This results in their inability to efficiently undergo intersystem crossing, leading to lower RTP efficiency. Therefore, we speculate that the photochromism observed in DPTZC1 may be due to the formation of DPTZC1+• radicals, a result of the photooxidation of DPTZC1 molecules within the PVA matrix. To assess the macroscopic photodeformation behavior, we prepared DPTZC1 in PVA films using a solution-processing method (Figure 3a). A film with a DPTZC1-to-PVA molar ratio of 1:60 was fabricated for this investigation (Figure 3b). Upon continuous UV irradiation for 60 s, the film exhibited a bending angle of ∼30°. Figure 3 | (a) Schematic of the UV-responsive deformation of DPTZC1 embedded in PVA through a solution-processing technique. (b) Before and after images illustrating the flexibility of DPTZC1 in PVA when exposed to 365 nm UV light for one minute under ambient conditions. (c) Schematic of the strain reversibility test. (d) Plot of the applied force versus the duration of UV exposure on the DPTZC1-doped PVA film. (e) Proposed mechanism of the UV-responsive reversible deformation of the DPTZC1-PVA system (molar ratio; DPTZC1:PVA = 1:60). Download figure Download PowerPoint We next conducted stress–strain experiments to examine the reversibility of the photoinduced film deformation. A standard-sized sample of 20 mm × 8 mm was used. Before testing, the film was sandwiched between two clips and prestretched with an initial stress of 10 mN (Figure 3c). After 30 s of UV irradiation, the deformation was quantified by the increase in force strength from 10 to 20 mN (Figure 3d). This strain released and automatically reverted to the initial state of 10 mN 30 s after turning off the UV light. The deformation was reversible for at least 15 cycles without obvious alteration. Further exploration into the effect of DPTZC1 doping concentration in PVA film on reversibility showed that a higher concentration (1:10) led to faster and higher film tension, reaching ∼40 mN under 30 s of UV irradiation at this doping level (see Supporting Information Figure S25). This indicates that the macroscopic deformation originates from the DPTZC1 molecules doped into the PVA film. We also investigated the photoinduced deformation of the other four PTZ derivatives in PVA films. None of these films exhibited macroscopic deformation after UV irradiation. This suggests that the significant macroscopic film deformation of DPTZC1 in PVA films is due to microscopic excited-state geometry variations, likely amplified by keto-enol tautomerism (Figure 3e). Notably, DPTZC1 crystals also undergo a color change after 365 nm irradiation (see Supporting Information Figure S26). A detailed examination of the UV–vis spectra revealed a significant enhancement at ∼447 nm. However, no EPR signal was observed. Analysis of the single crystal of DPTZC1 indicated that the color change might originate from enhanced intermolecular interactions, as evidenced by the slightly reduced centroid–centroid distance (3.751–3.741 Å) in the π–π stacking following UV irradiation (see Supporting Information Figures S27 and S28). To unravel the underlying mechanisms of RTP and photodeformation in DPTZC1, we performed DFT calculations to model its photophysical properties. The modeling was conducted at the ωB97XD/TZVP level using a polarizable continuum model in ethanol. Analysis in the optimized S0 geometry revealed that the highest occupied molecular orbital is primarily located on the PTZ subunit in both the diketone and keto-enol forms of DPTCZ1. Conversely, the lowest unoccupied molecular orbital spans the entire molecule, with this delocalization being more pronounced in the diketone form (see Supporting Information Figure S29). The calculated orbital overlap integral was 0.63. The partial separation of orbitals leads to a relatively large singlet-triplet energy gap (ΔEST: ∼1.35 eV, Figure 4a). It is important to note, however, that there are multiple higher-lying triplet excited states between the first singlet excited state (S1) and the first triplet excited state (T1). These states potentially act as reporter states for triplet excitons (see Supporting Information Figure S28). In the optimized S1 geometry, multiple singlet and triplet intersystem crossing (ISC) channels with spin–orbit coupling constants over 1.2 cm−1 were predicted (see Supporting Information Figure S30). This efficient ISC facilitates an effective spin-flip to the triplet state. Upon examining the relaxed T1 geometry, T1 spin density analysis suggested that triplet emission is dominated by the keto-enol geometry of DPTZC1 (T1 = 2.08 eV) compared with the measured RTP emission maximum T1 = 2.33 eV, estimated from the onset of RTP emission at 77 K (see Supporting Information Figure S15). The emission mainly originates from the local exciton emission of the PTZ subunit (Figure 4b, see Supporting Information Figure S31). Figure 4 | (a) Vertical excitation energy levels of DPTZC1 between keto-enol geometry and diketone geometry calculated using optimized S0 geometry in ethanol at the ωB97XD/TZVP level. (b) T1 spin density distributions (isovalue: 0.0004) and T1 vertical emission energies of DPTZC1 between the keto-enol geometry and the diketone geometry calculated in ethanol at the T1 optimized geometry at the ωB97XD/TZVP level. (c) RMSD of DPTZC1 between the keto-enol geometry and the diketone geometry in the relaxed S1 state (top) and in the radical state (bottom). Download figure Download PowerPoint To investigate the cause of the photodeformation observed in DPTZC1, we focused on analyzing the structural differences between its diketone and keto-enol forms. This analysis involved calculating the root mean square displacement (RMSD) to measure the extent of structural deviation between these two geometries. When examining the relaxed geometry of S1, we observed a relatively large structural deviation expressed quantitatively with an RMSD value of 3.72 (Figure 4c). This marked microscopic structural variation is crucial as it translates into the observed macroscopic deformation of the film. Furthermore, the RMSD calculations in the radical state also revealed a considerable structural deformation, with an RMSD of 2.98. This finding is noteworthy as it highlights the structural changes occurring at the molecular level upon excitation. An important aspect of this system is the role played by PVA. To investigate the effect of the matrix on the phosphorescence properties of the materials, another polymer, PE, was introduced into the doping system. Its corresponding photoactivated RTP and chromic properties were then investigated for comparison (see Supporting Information Figure S24), which showed no significant changes before and after UV irradiation. This further proves that PVA is able to provide robust hydrogen bonds that aid in stablizing triplet excitons. Upon light irradiation, this stabilization mechanism facilitates the tendency of keto-enol tautomerism to favor the enol structure. This keto-enol tautomerism not only stabilizes the radicals at the molecular level but also manifests macroscopically as the observed photoinduced deformation for the material, thus providing another method for the construction of new functional materials including RTP ones for potential applications.47–52 Leveraging the unique attributes of RTP as well as the processability, flexibility, and recoverability of DPTZC1-doped PVA films, we have conceptualized several potential applications. These films are produced through a drop coating method, where DPTZC1 is dispersed in a PVA solution containing 3 wt % DMSO. We emulated the dynamic curvature of a frog's tongue under UV irradiation to demonstrate the film's responsive and adaptive nature (Figure 5a). Moreover, we created a biomimetic mimosa leaf using the DPTZC1-PVA mixture at a ratio of 1:60. This leaf model exhibits gradual curling in response to the duration of UV light exposure (Figure 5b). The DPTZC1-PVA film system can also be employed in anticounterfeiting and information display technologies (Figure 5c). One of the most important properties of this flexible film is its strong yellow–green afterglow, which is prominently visible even at room temperature after ceasing exposure to a 365 nm UV torch. Figure 5 | (a) Schematic illustration and photographs of the DPTZC1 in PVA simulating tongue muscle curl in frogs (Molar ratio of DPTZC1:PVA = 1:10). (b) Schematic illustration and photographs of the DPTZC1 in PVA simulating mimosa curlin