Visible light-initiated rapid self-healing of PDMS elastomers engineered through dual dynamic bonding networks for smart sensors

Abstract

Light-activated self-healing materials, which enable remote control with high spatiotemporal resolution, have recently garnered significant attention across diverse fields. However, in most cases, high-energy ultraviolet (UV) light is often required to initiate dynamic covalent bond exchange, and the repair processes take a long time (>12 h). In this work, we reported a PDMS elastomer tailored by dynamic telluride bonds and hydrogen bonds, demonstrating rapid self-healing capabilities under both UV and visible light irradiation. The light-responsive behavior of this polymer arises from the unique ability of telluride bonds to generate highly reactive telluride radical complexes under multi-wavelength light exposure. By integrating dual dynamic bonds (hydrogen bonds and telluride bonds), the Te–Te–PDMS elastomers exhibited exceptional mechanical properties (tensile strength: 1.0 MPa; elongation at break: 1390%) and rapid self-healing efficiency, achieving 98% strength recovery within 30 minutes under UV light and 97% recovery within 60 minutes under xenon light. This study presents a novel approach for designing self-healing polymers with dynamic covalent bonding systems, while advancing the prosperity of dynamic chemistry.

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New concepts

We present a class of multi-band photo-responsive rapid self-healing polydimethylsiloxane (PDMS) elastomers crosslinked through dynamic ditelluride bonds and hydrogen-bonding networks. Time-dependent density functional theory (TD-DFT) was applied to investigate the excited-state properties of ditelluride monomers, unravelling the light-activated dynamic exchange mechanism of ditelluride bonds at the electronic structure level. Integrated analytical techniques, including in situ infrared spectroscopy and electron paramagnetic resonance (EPR), revealed that the self-healing process arises from synergistic interactions between hydrogen bond reorganisation and light-initiated ditelluride bond metathesis. This dual dynamic mechanism enables the system to recover 98% of its tensile strength within 30 minutes under ultraviolet irradiation and 97% after 1 hour of visible light exposure. Compared to conventional UV-driven self-healing systems, the multi-wavelength-responsive ditelluride platform demonstrates enhanced performance, featuring accelerated repair kinetics and superior healing efficiency. These attributes facilitate adaptation to diverse operational requirements while exhibiting significant potential for applications in healthcare technologies and advanced sensing systems.

1. Introduction

Natural systems exhibit inherent damage auto-repair mechanisms, which is a vital evolutionary adaptation for prolonging organismal viability. Drawing inspiration from these biological systems, materials science has driven the emergence of synthetic self-restorative systems capable of autonomous physical rehabilitation, thereby extending material operational longevity.^1–3 Current polymer engineering deploys two distinct methodologies to realize self-healing functionality: extrinsic and intrinsic methods.^4,5 Extrinsic systems are typically engineered through the integration of microencapsulated healing agents or embedded vascular networks within polymeric matrices.^6,7 Upon crack initiation, repair agents are released at the damaged sites and subsequently solidify the fractured surfaces. This extrinsic approach offers advantages such as rapid reaction kinetics and high repair efficiency. However, when designing extrinsic self-healing systems, the following factors need to be considered: (i) the impact of the embedded carriers containing the healing agent on the mechanical properties of the host matrix and (ii) the finite shelf life of catalytic components.^5,8 Furthermore, extrinsic repair agents exhibit limited repair cycles, rendering them ineffective for repeated damage events. In contrast, intrinsic systems enable polymer self-healing through dynamic covalent bonds or non-covalent interactions. As the healing process is inherently reversible, intrinsically self-healing materials theoretically permit infinite repairs at the same damaged locus. Consequently, these systems represent a highly promising strategy for sustainable material design.

In covalently cross-linked networks engineered through dynamic bonds, reversible dissociation and reformation of these bonds are typically triggered by external stimuli, including temperature,^9,10 pH,^11,12 light,^13,14 and solvent mediation.^15,16 Among these, light-initiated dynamic covalent systems offer distinct advantages including versatile modes of light introduction, tunable wavelengths, adjustable light intensity and polarisation, exceptional temporal and spatial resolution, and the absence of chemical contamination. These characteristics have rendered photo-activated dynamic combinatorial chemistry a subject of considerable interest. Recently, light-initiated dynamic combinatorial chemistry, including the trans–cis isomerization of azobenzene,^14,17 isomerization of spiropyran,¹⁸ photoinduced π-electrocyclization of diarylethenes,¹⁹ and metathesis of chalcogen–chalcogen bonds,^20,21 has been extensively applied to the design of self-healing polymers. Nevertheless, such systems predominantly required high-energy ultraviolet (UV) irradiation to facilitate dynamic covalent bond exchange, with repair durations typically exceeding 12 h in most cases. Nevertheless, prolonged UV exposure risks compromising polymer chain integrity, accelerating material ageing, and degrading functional properties, which turns into a critical limitation impeding the practical deployment of these self-healing systems.²⁰ This necessitates the development of rapid dynamic exchange systems operable under milder activation conditions, such as visible-light-driven dynamic covalent systems. However, research efforts in this domain remain notably scarce.

As a chalcogen element, tellurium exhibits a greater atomic radius and reduced electronegativity compared to sulphur and selenium, conferring distinct physicochemical properties.²² Research studies have demonstrated that disulphide and diselenide bonds undergo metathesis when activated by ultraviolet (365 nm) and visible light (410 nm) irradiation, respectively.^13,20,23 Particularly, polymers incorporated with diselenide linkages achieved physical damage restoration on material surfaces following 24 h xenon lamp irradiation. Nevertheless, visible-light-induced repair processes in diselenide-based polymers exhibit prolonged durations, frequently necessitating a supplementary thermal input to accelerate dynamic exchange reactions.²⁴ Compared with disulfide and diselenide bonds, the telluride bond demonstrates a substantially lower bond energy (Te–Te: 126 kJ mol⁻¹; Se–Se: 172 kJ mol⁻¹; S–S: 240 kJ mol⁻¹).²⁵ This thermodynamic profile suggests potentially reduced photon energy requirements for initiating ditelluride bond metathesis. Nevertheless, research into self-healing systems mediated by telluride bond metathesis remains scarce. Furthermore, the photochemical mechanisms underlying the light-triggered dynamic reorganisation of these bonds, and their consequent influence on polymeric self-healing efficacy, have yet to be fully elucidated.

In this study, we synthesised a series of Te–Te–PDMS elastomers with multi-wavelength light-activated self-healing capabilities. These elastomers employ a dual cross-linking architecture combining dynamic ditelluride bonds and hydrogen bonding interactions, thereby conferring enhanced mechanical robustness to the polymeric networks. Crucially, the ditelluride moieties exhibit wavelength-flexible metathesis behaviour, undergoing dynamic exchange under both UV and visible light irradiation via a radical-mediated mechanistic pathway. The strategic incorporation of ditelluride bonds into PDMS backbones enables rapid room temperature repair under polychromatic light initiation, advancing the design of dynamic covalent self-healing systems. To demonstrate practical utility, high-conductivity silver nanowire (AgNW) layers were integrated with Te–Te–PDMS substrates, and obtained conductive AgNWs/Te–Te–PDMS composites. These conductive composites have been successfully implemented as intelligent sensing interfaces for flexible electronics and electrophysiological monitoring applications.

2. Results and discussion

2.1. Structural design and preparation of Te–Te–PDMS

The architectural design and synthetic route for PDMS elastomers tailored by dual dynamic bonds are illustrated in Fig. 1a and Fig. S7 (ESI†). First, bis(3-aminopropyl)-terminated poly(dimethylsiloxane) (NH₂–PDMS–NH₂) was utilized as a flexible backbone. 3-(Isocyanatomethyl)-3,5,5-trimethylcyclohexyl isocyanate (IPDI) was employed as a chain extender. Next, 2,2′-ditellanediyldianiline (NH₂–Te–Te–NH₂) serving as the hard chain segment was added to introduce dynamic covalent bonds into the elastomer. Comprehensive synthetic procedures and spectroscopic characterisation of the NH₂–Te–Te–NH₂ monomer are detailed in Fig. S1–S6 and Table S1 (ESI†). To engineer enhanced self-restorative functionality, the system incorporates synergistic dynamic interactions through covalent ditelluride bonds and quadruple hydrogen bonding networks. As depicted in Fig. 1b, the strategic integration of NH₂–Te–Te–NH₂ monomers introduced photoresponsive ditelluride linkages, while amine–isocyanate conjugation established reversible hydrogen bonds. This dual dynamic system facilitated molecular chain reorganisation through radical-mediated ditelluride metathesis under multi-wavelength light exposure (Fig. 1c), enabling rapid autonomous repair while maintaining structural integrity.

Fig. 1 Schematic representation of the architectural design and dynamic bonding networks in Te–Te–PDMS elastomers. (a) Molecular architecture of Te–Te–PDMS. (b) Dual dynamic interactions: non-covalent (hydrogen bonds) and covalent (ditelluride bonds) interactions. (c) Wavelength-dependent photoresponsive behaviour mediated by ditelluride metathesis reactions under visible irradiation.

Comprehensive spectroscopic characterisation was employed to elucidate the structural architecture of the polymeric system.¹H-NMR spectral analyses of the precursor compounds and synthesised Te–Te–PDMS elastomers are presented in Fig S3, S8 (ESI†) and Fig. 2a, b. Characteristic aromatic proton resonances at 7.66, 7.16, 6.77 and 6.50 ppm (Fig. 2a and b) correspond to benzene rings adjacent to ditelluride bonds,^15,26 confirming successful integration of Te–Te bonds within the PDMS backbone. Fourier-transform infrared (FT-IR) spectroscopic investigations revealed critical structural transformations (Fig. 2c, blue spectrum). The disappearance of the 2244 cm⁻¹ absorption band, diagnostic of isocyanate (–NCO) stretching vibrations in IPDI,^16,27 coincides with the emergence of new spectral features: (i) a 1629 cm⁻¹ band corresponding to carbonyl (C=O) stretching^15,28 and (ii) two distinct absorptions at 1570 cm⁻¹ (N–H bending) and 3338 cm⁻¹ (N–H stretching) characteristic of urethane (–NH–CO–O–) groups.^27,29 These spectroscopic changes conclusively demonstrated the anticipated amine–isocyanate conjugation between –NH₂ and –NCO functional groups, verifying successful polymer network formation.

Fig. 2 Structural characterisation of Te–Te–PDMS elastomers. (a) ¹H NMR spectrum of Te–Te–PDMS recorded in deuterated chloroform (CDCl₃). (b) Expanded spectral region of the highlighted protons in (a). (c) Comparative FT-IR analysis of IPDI, NH₂–PDMS–NH₂ precursors, and Te–Te–PDMS elastomers. (d) XPS survey spectra of NH₂–Te–Te–NH₂ monomers and Te–Te–PDMS elastomers. (e)–(h) High-resolution XPS deconvolution: (e) Te 3d and (f) C 1s core-level spectra of NH₂–Te–Te–NH₂ and (g) Te 3d and (h) C 1s spectra of Te–Te–PDMS.

X-ray photoelectron spectroscopy (XPS) analyses of NH₂–Te–Te–NH₂ and Te–Te–PDMS provided corroborative evidence for the proposed reaction mechanism. The survey spectrum of NH₂–Te–Te–NH₂ (Fig. 2d) demonstrated the presence of tellurium, carbon, nitrogen, and oxygen through characteristic elemental emission signatures. High-resolution Te 3d spectra revealed spin–orbit splitting into dual energy levels (j = 3/2 and j = 5/2),³⁰ with distinct binding energies at 583.2 eV (Te 3d3/2, Te–Te/Te–C bonds) and 572.8 eV (Te 3d5/2, Te–Te/Te–C bonds),³¹ as shown in Fig. 2e. Crucially, these tellurium speciation signatures persisted in Te–Te–PDMS spectra (Fig. 2g), confirming successful incorporation of ditelluride bonds into the PDMS backbone. Deconvolution of C 1s spectra further substantiates the chemical transformations. Peaks of NH₂–Te–Te–NH₂ monomers at 284.8 eV and 285.5 eV originated from C–C/C=C and C–N bonds, respectively^32,33 (Fig. 2f). Three components of Te–Te–PDMS elastomers, located at 284.8 eV, 285.8 eV, and 289.1 eV, originated from C–C/C=C, C–N, and C=O groups, respectively^15,34 (Fig. 2h). The emergence of the carbonyl (C=O) signature provides further evidence of amine–isocyanate conjugation between –NH₂ and –NCO groups. Collectively, these spectroscopic findings validate the successful synthesis of ditelluride-functionalised PDMS elastomers through the targeted reaction of amino-terminated precursors with IPDI, as schematically represented in Fig. 1a.

Furthermore, the physicochemical characteristics of the synthesised elastomers, including mechanical robustness, optical absorption/transmission profiles, and thermal stability of the elastomers, could be tuned by the stoichiometric ratios of NH₂–Te–Te–NH₂ and NH₂–PDMS–NH₂, as shown in Fig. S9–S14 and Fig. S15 (ESI†) demonstrates the temperature dependence of the storage (E′), loss (E′′) modulus and tanδ for optimized the Te–Te–PDMS elastomer by dynamic mechanical analysis (DMA). As shown in Fig. S15 (ESI†), the DMA curve of the Te–Te–PDMS elastomer exhibited two E′–E′′ crossover points, reflecting multiple relaxation processes caused by the microphase-separated structure within the material. The crossover point in the low-temperature region (below −80 °C) may correspond to the glass transition of the flexible chain segments (NH₂–PDMS–NH₂), while the crossover point in the high-temperature region (0–40 °C) likely corresponds to the glass transition or melting of the rigid chain segments (NH₂–Te–Te–NH₂), which is consistent with the block copolymer molecular structure we have designed.

2.2. Self-healing behavior of Te–Te–PDMS elastomers

Over recent decades, significant research efforts have focused on developing materials with self-healing capabilities to address environmental challenges posed by the slow degradation rates and poor recyclability of conventional polymers.^4,9,35,36 The Te–Te–PDMS elastomer demonstrated promising autonomous repair potential at ambient temperatures through the strategic incorporation of dynamic ditelluride bonds and hydrogen bonds within its polymer matrix. A comprehensive experimental investigation was conducted to evaluate the self-healing performance of Te–Te–PDMS specimens under varying environmental conditions. Recovery metrics were quantified through percentage comparisons between healed and pristine samples for both tensile strength retention and elongation at break restoration.

Primary investigations examined the influence of illumination conditions on repair efficacy. Specimens underwent 30 min healing intervals under four distinct regimes: dark conditions, blue light (460 nm), xenon lamp illumination, and UV light (365 nm). Fig. 3a and b presents the stress–strain profiles and corresponding recovery ratios, revealing tensile strength restoration rates of 98%, 83%, 77% and 51%, respectively, for UV, blue light, xenon illumination and dark conditions. It should be noted that an infrared camera was employed to monitor the temperature rise on the elastomer surfaces during a 10-minute illumination period. The results demonstrated that under irradiation from all three light sources, the equilibrium surface temperature of the elastomer did not exceed 35 °C (Fig. S16, ESI†), suggesting that the temperature increase induced by the light had a negligible impact on the self-healing performance of the Te–Te–PDMS elastomer. These findings demonstrated that photonic activation significantly enhanced the mechanical property restoration of Te–Te–PDMS elastomers. Furthermore, the material's exceptional self-healing capacity enabled complete morphological restoration within the 30-minute repair window, as evidenced by the visual documentation in Fig. 3c.

Fig. 3 Photoresponsive self-healing performance of Te–Te–PDMS (R = 2 : 8) elastomers. (a) Stress–strain profiles of pristine vs. healed samples after 30 min irradiation under distinct light sources. (b) Quantified recovery ratios for tensile stress (σ) and elongation at break (ε) post-healing under relevant irradiation conditions. (c) Macroscopic visualisation of the crack closure before and after photomediated repair. (d) Temporal evolution of the mechanical recovery under xenon lamp irradiation (5 mW cm⁻²). (e) σ and ε recovery as a function of irradiation duration (0–60 min). (f) Wavelength, healing duration, and healing efficiency of the reported light-activated self-healing systems.^{13,14,16,21,37,38} (g) In situ time-lapse optical microscopy imaging of interfacial healing (0/10/30/60 min intervals).

Moreover, the self-healing efficacy of Te–Te–PDMS specimens under xenon illumination was systematically investigated across varying exposure durations. As illustrated in Fig. 3d and e, both tensile strength and elongation-at-break restoration percentages demonstrated a progressive enhancement with increased exposure time. Specimens subjected to 60 min of xenon illumination achieved near-complete recovery, with the tensile strength and elongation-at-break restoration levels reaching 97% and 95%, respectively. Fig. 3f comparatively analyses the repair kinetics and efficiencies of reported photoactivated self-healing systems.^{13,14,16,21,37,38} Notably, the ditelluride-containing Te–Te–PDMS specimens exhibited markedly accelerated repair kinetics relative to benchmark systems, alongside significantly reduced energy demands for bond reorganisation. Furthermore, the Te–Te–PDMS elastomer demonstrated excellent healing capabilities over five time cutting-healing cycles (Fig. S17, ESI†).

The recovery process of damaged specimens under xenon lamp illumination was monitored in situ via optical microscopy. As shown in Fig. 3g, progressive reduction of the fracture surface was observed over a 60-minute healing period, with complete morphological restoration achieved at the endpoint. The initial contact of the separated halves (0-minute healing duration) exhibited micrometre-scale interfacial gaps, while prolonged illumination facilitated gradual scar resolution until full cohesion was attained. Subsequent tensile testing evaluated elongation recovery in specimens subjected to 30-minute xenon illumination (Fig. S18, ESI†). Both pristine and repaired specimens demonstrated comparable extensibility, sustaining approximately 800% strain prior to failure, thereby confirming restored mechanical integrity. We further studied the recovery of the Te–Te–PDMS samples’ mechanical properties under natural daylight. As depicted in Fig. S19 (ESI†), after 4 h of sunlight-assisted repair during afternoon temperatures of 31–35 °C, both the tensile strength and elongation at break recovered to over 80%. In addition, the PDMS elastomers both before and after the self-healing process were stretched and released under 100% strain over successive cycles (1000). As presented in Fig. S20 (ESI†), the area of the hysteresis loop decreased somewhat in the initial 20 cycles but could be stable in subsequent cycles, demonstrating the long-term durability and excellent fatigue resistance of Te–Te–PDMS elastomers both prior to and following self-healing.

2.3. Self-healing mechanism of Te–Te–PDMS elastomers

Generally, the self-healing mechanism of intrinsic self-repairing materials generally comprises three key stages: (i) mobility and diffusion of molecular chain segments, (ii) recontacting of dissociated active sites, and (iii) reformation of dynamic bonds and reconfiguration of cross-linking networks.³⁹ In the present system, the Te–Te–PDMS elastomers exhibited a glass transition temperature (T_g) of approximately −120 °C (Fig. S11b, ESI†). This sub-ambient T_g ensured that the material retained sufficient molecular mobility to enable segmental diffusion under ambient conditions (25 °C), fulfilling the first-stage requirement for autonomous repair. Additionally, the molecular chains of Te–Te–PDMS elastomers contain numerous N–H and C=O functional groups, which facilitated the formation of both intramolecular and intermolecular hydrogen bonds.^16,28 As a characteristic category of dynamic non-covalent interactions, hydrogen bonds exhibited reversible dissociation and reconstruction under specific conditions. This dynamic behaviour played a crucial role in the restoration of crosslinked network structures.^9,15 The formation of hydrogen bonding interactions induces a discernible lengthening of carbonyl bond distances, manifesting as reduced frequency values in carbonyl stretching vibrations.⁹ Consequently, in situ infrared spectroscopy has become an established analytical technique for investigating hydrogen bonding phenomena in these systems. Fig. 4a presents temperature-dependent in situ FTIR spectra of the Te–Te–PDMS specimen across the 25–150 °C range. Thermogravimetric analysis confirmed that no polymer degradation occurred within this temperature interval (Fig. S11a, ESI†). The absorbance peaks at approximately 1572 cm⁻¹ and 1627 cm⁻¹ were assigned to hydrogen-bonded C=O stretching vibrations and N–H bending vibrations, respectively. These spectral features exhibited progressive intensity reduction with rising temperatures. Notably, the 1627 cm⁻¹ peak underwent a blueshift to 1629 cm⁻¹, while the 1572 cm⁻¹ peak redshifted to 1570 cm⁻¹, indicative of thermal conversion from hydrogen-bonded C=O/N–H associations to free functional groups. Collectively, these observations demonstrated the material's inherent hydrogen-bond abundance under ambient conditions (25 °C), with dynamic reconstruction of this cross-linking network enabling partial mechanical restoration in Te–Te–PDMS elastomers, providing a mechanistic rationale for retained self-healing capability under dark conditions where telluride bond activity is minimal (Fig. 3a). In addition to the contribution of dynamic hydrogen bonding, the light-initiated metathesis reaction of ditelluride bonds is posited to enhance the self-healing efficiency of Te–Te–PDMS samples. To validate the radical-mediated exchange mechanism, electron paramagnetic resonance (EPR) spectroscopy was conducted under varying light conditions. The spin-trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was employed to capture transient tellurol radical intermediates. As illustrated by the black curves in Fig. 4b and c, no radical signal was observed under dark conditions. However, upon exposure of the samples to UV or xenon light for two minutes, the DMPO-tellurol radical signal emerged immediately. The emergence of these spectral signatures is attributable to the cleavage effect of the nitrogen atom and the β-hydrogen abstraction and nitrogen-centred radical stabilisation mechanisms,⁴⁰ with the reactions between ditelluride and DMPO depicted in Fig. S21 (ESI†). Under different light conditions, the EPR spectra exhibited different signal intensities, indicating different radical stabilities.²⁰ Furthermore, the test results revealed that the isotropic EPR signals (g value) of the Te–Te–PDMS samples under UV light and xenon light irradiation were 2.00727 and 2.00699, respectively, corresponding to the value of a free electron (2.0023). Thus, the EPR results confirmed that light irradiation leads to the conversion of ditelluride bonds to tellurol radicals in Te–Te–PDMS elastomers, which means that there are more reactive sites. Moreover, the Te–Te–PDMS molecular chains have good mobility at room temperature, as analysed above, which was favourable for the reorganization of ditelluride bonds and the randomization of the interface. As a result, Te–Te–PDMS elastomers could achieve rapid self-healing under UV light and visible light irradiation.

Fig. 4 Mechanistic elucidation of Te–Te–PDMS self-healing behaviour. (a) Time-resolved FT-IR spectral evolution of Te–Te–PDMS under 30–150 °C. (b) and (c) In situ EPR spectra under (b) UV light and (c) xenon lamp irradiation, confirming radical-mediated bond exchange. (d) and (e) DFT-optimized geometries: (d) ground-state (S₀) vs. (e) excited-state (S₁) configurations of NH₂–Te–Te–NH₂, revealing Te–Te bond elongation (2.85 Å → 3.12 Å). (f) Electron density difference isosurfaces (isovalue = 0.005) for S₀ → S₁ transition of NH₂–Te–Te–NH₂. The red and ice-blue regions correspond to the increased and decreased electron density post-excitation, respectively. (g) Proposed mechanistic framework integrating radical recombination and hydrogen bond reorganisation during photothermal healing.

Here, we studied the physical properties of NH₂–Te–Te–NH₂ molecules through quantum chemical simulations to advance the understanding of ditelluride bond metathesis exchange mechanisms and facilitate practical implementation. Fig. 4d presents the optimised ground-state geometry (S₀ state) of NH₂–Te–Te–NH₂ calculated at the PBE/def2-TZVP level, which served as the reference coordinate system for all subsequent molecular orientation analyses. As shown in Fig. 4d, the structural characteristics of the Te–Te bond were well exemplified by NH₂–Te–Te–NH₂, exhibiting a Te–Te bond length of 2.73 Å and a C–Te–Te–C dihedral angle of 60.7°. These parameters showed close agreement with published data for the aliphatic ditellurides of the type RTe–TeR.²⁴

The time-dependent density functional theory (TD-DFT) method was systematically performed to study the excited-state characteristics of NH₂–Te–Te–NH₂ molecules. The optimised excited-state geometry (S₁ state) of NH₂–Te–Te–NH₂ was obtained, as illustrated in Fig. 4e. The computational results revealed a significant structural alteration in NH₂–Te–Te–NH₂ following the S₀ → S₁ electronic transition, predominantly manifested by an elongation of the Te–Te bond distance. The electron density difference between the ground and excited states (S₀ → S₁) was analysed using the Multiwfn 3.7 (dev) code.⁴¹ As demonstrated in Fig. 4f, the red and ice-blue regions correspond to the increased and decreased electron density post-excitation (isovalue = 0.005), respectively. Notably, upon S₀ → S₁ excitation, electron density redistribution occurs predominantly around the tellurium atoms: a decrease in the bonding orbital region (ice-blue) and an increase in the antibonding orbital region (red). Analysis of the molecular orbital characteristics further indicates that the S₀ → S₁ transition in NH₂–Te–Te–NH₂ corresponds to a π → π* excitation.

Furthermore, the excitation energies and oscillator strengths of the first 50 excited states were calculated, and the simulated UV-vis absorption spectrum of the NH₂–Te–Te–NH₂ molecule was generated based on these data, as illustrated in Fig. S22a (ESI†). A prominent absorption band spanning 300–500 nm (peak at 388 nm) was observed, arising from the S₀ → S₁ (461 nm), S₀ → S₂ (397 nm), and S₀ → S₃ (362 nm) electronic transitions. Further electronic structure analysis revealed the molecular orbitals (MO) involved in these transitions. These transitions were dominated by the MO₇₃ → MO₇₄, MO₇₂ → MO₇₄, and MO₇₁ → MO₇₄ transitions, respectively, with the relative contributions of these transitions detailed in Fig. S23 (ESI†). Crucially, computational results demonstrated that the first three excited states of NH₂–Te–Te–NH₂ exhibited intrinsic correlations with the structural configuration of ditelluride bonds. The experimental UV-vis absorption spectrum (Fig. S22b, ESI†) displayed strong agreement with the simulated predictions (Fig. S22a, ESI†). Collectively, these findings suggested that ditelluride-containing molecules undergo photoinduced molecular orbital transitions under ultraviolet or visible light irradiation, generating highly reactive telluride radicals. This mechanistic insight provides a coherent explanation for the light-initiated metathesis behaviour of ditelluride bonds.

By combining the excited-state characteristics of the NH₂–Te–Te–NH₂ monomers, obtained from TD-DFT calculations (Fig. S22 and S23, ESI†), with the repair efficiencies observed under different wavelengths of light (Fig. 3a and b), we concluded that under blue light, Te–Te–PDMS molecules primarily underwent an S₀ → S₁ transition (461 nm), generating highly reactive self-healing sites (tellurol radicals). However, as shown in Fig. S22 (ESI†), the oscillator strength of this transition is relatively low, leading to a correspondingly low healing efficiency in the Te–Te–PDMS elastomer. The xenon lamp used in the experiments emitted predominantly within the 400–780 nm range, which could induce both S₀ → S₁ (461 nm) and S₀ → S₂ (397 nm) transitions in Te–Te–PDMS molecules. Since the latter transition has a higher oscillator strength, the elastomer exhibited greater healing efficiency under this irradiation. Furthermore, ultraviolet light could promote S₀ → S₂ (397 nm) and S₀ → S₃ (362 nm) transitions, both of which possess high oscillator strengths, thus resulting in the highest healing efficiency for the elastomer within 30 minutes.

Based on the aforementioned analyses, it is proposed that the superior self-healing performance of Te–Te–PDMS elastomers primarily arose from the light-initiated metathesis of ditelluride bonds, involving their reversible cleavage and reformation on the fractured surfaces of the samples. Additionally, dynamic hydrogen bond reorganisation contributes synergistically to the self-healing process. A schematic representation of this dual-mechanism is presented in Fig. 4g. Crucially, the high chain mobility and efficient molecular diffusion within the polymer matrix enable autonomous self-repair under ambient conditions.

2.4. Application of Te–Te–PDMS elastomers

The Te–Te–PDMS elastomers, engineered through dynamic ditelluride bonds and hydrogen bonds, demonstrated outstanding mechanical robustness and self-healing capabilities, positioning them as promising candidates for flexible strain-sensing applications. To exploit these properties, silver nanowires (AgNWs), with high optical transparency and superior electrical conductivity, were incorporated as fillers via spray-coating onto Te–Te–PDMS substrates, yielding conductive polymer composites (AgNWs/Te–Te–PDMS). Fig. 5a schematically depicts the composite's fabrication protocol, while Fig. 5b, c and Fig. S24–S28 (ESI†) characterized the structures of the AgNWs. The composite's macroscopic homogeneity is demonstrated in Fig. 5d, with detailed interfacial analysis provided in ESI† micrographs.

Fig. 5 Fabrication and structural characterisation of AgNWs/Te–Te–PDMS composites. (a) Fabrication workflow of AgNWs/Te–Te–PDMS composites. (b) and (c) Morphologies of AgNWs and Ag: (b) TEM image and (c) EDS elemental mapping. (d) Digital photograph of the free-standing composite film. (e)–(g) Microstructure of AgNWs/Te–Te–PDMS composites: (e) optical micrograph showing the AgNWs’ percolation network, (f) surface topography by SEM, and (g) cryo-fractured cross section revealing the thickness of the conductive layer.

The conductive network architecture of the composites was systematically investigated using optical microscopy and scanning electron microscopy (SEM). Owing to the inherent optical transparency of the Te–Te–PDMS elastomers, the three-dimensional percolative network formed by silver nanowires (AgNWs) was clearly visible under optical microscopy (Fig. 5e). AgNWs with a high aspect ratio established an interconnected, scaffold-like conductive framework within the polymer matrix, conferring superior electrical conductivity to the composites. Remarkably, the AgNW conductive layer minimally impacts the composite's optical transmittance, as quantified in Fig. S27 (ESI†). The SEM micrographs (Fig. 5f and g) further revealed that discrete nanowires assembled into thickness-tunable conductive networks.

Fig. 6a illustrates the strain-dependent response of AgNWs/Te–Te–PDMS composites, characterized by a monotonic increase in the normalized resistance change (ΔR/R₀) with applied tensile strain, operating within a 0–45% strain range. Notably, the linear response regime (0–10% strain range) achieved a gauge factor (GF) of 4.7. Fig. 6b–d demonstrates the composite's capabilities for real-time monitoring of biomechanical activities, including finger flexion, wrist articulation, and phonation activity. When mounted onto human subjects, the sensor exhibited consistent signal fidelity during both subtle laryngeal vibrations during speech and high-amplitude joint movements, maintaining stable baseline recovery under cyclic loading. This functionality validated its suitability for wearable biomechanical sensing applications requiring high dynamic-range detection.

Fig. 6 Multimodal applications of Te–Te–PDMS elastomers in wearable sensing technologies. (a) Strain-dependent resistive response of AgNWs/Te–Te–PDMS composites (GF = 4.7). (b)–(e) Biomechanical sensing capabilities: (b) finger flexion tracking (0–90° range), (c) wrist articulation monitoring and (d) laryngeal vibration detection during phonation. (e) Wireless epidermal electrophysiological platform with Bluetooth telemetry. (f) ECG acquisition. (g) Phalangeal motion capture: (i)–(v) sequential flexion of the digits (thumb to the little finger). (h) Temporally correlated EMG signals during digit actuation.

Beyond strain sensing applications, the AgNWs/Te–Te–PDMS composites demonstrated multifunctional utility as dry epidermal electrodes for human electrophysiological monitoring. While conventional Ag/AgCl hydrogel electrodes retain the clinical standard for electrocardiogram (ECG) and electromyography (EMG) signal acquisition, their practical limitations, including hydrogel dehydration-induced performance degradation under ambient conditions and risks of cutaneous hypersensitivity reactions,⁹ necessitated alternative solutions. The solvent-free AgNWs/Te–Te–PDMS system addresses these challenges through intrinsic elastomeric compliance and stable bulk conductivity, enabling conformal epidermal interfacing without allergic risks. As schematised in Fig. S28 (ESI†), the wireless monitoring platform integrated a battery-powered acquisition unit with Bluetooth telemetry, interfaced via two AgNWs/Te–Te–PDMS electrodes. Fig. 6e and f demonstrates high-fidelity ECG capture from precordial placement, with all characteristic waveform components (P, Q, R, S, T, and U) resolved at clinical-grade resolution. Parallel EMG monitoring capabilities were validated through forearm-mounted electrodes (medical tape adhesion), where Fig. 6g and h exhibits temporally correlated signal responses to phalangeal flexion-extension cycles. Distinctive signal peaks were observed during dynamic movements, while quiescent states maintained electrophysiological silence. Crucially, each digit's motion profile generated unique neuromuscular activation patterns, demonstrating the system's capacity for gesture discrimination in kinematic analysis. These results indicated that Te–Te–PDMS elastomers could act as versatile platforms for integrated wearable diagnostics spanning clinical medicine and biomechanical research.

Furthermore, the self-healing behaviour of the conductive AgNWs/Te–Te–PDMS composites was investigated. Initially, the conductive composite was connected to a 12 V circuit with a light-emitting diode (LED) bulb, which emitted a bright blue light (Fig. 7a). Subsequently, the conductive composite was cut into two segments using a razor blade, resulting in the immediate extinguishing of the LED bulb (Fig. 7b). The damaged composite was then subjected to repair under exposure to a xenon lamp, as shown in Fig. 7d. After 1 h of healing, the LED bulb resumed emitting light (Fig. 7c). The evolution of the surface structure of the conductive composite was observed using an optical microscope. As illustrated in Fig. 7e–g, the damaged conductive composite exhibited micron-sized grooves within its conductive layer and elastomer matrix. Following 1 h of healing, the physical damage to the elastic matrix was entirely restored, and the damaged area of the conductive layer significantly reduced, allowing the conductive pathways formed by silver nanowires to be re-established. Test results of the composite's resistivity indicated that both once-repaired and twice-repaired composites were able to restore their conductivity (Fig. 7h). Fig. 7i and j show the ECG curves obtained from the original and healed AgNWs/Te–Te–PDMS composites acting as sensing electrodes. It was noted that all characteristic waveform components (P, Q, R, S, T, and U) were resolved at high resolution, suggesting a recovery of the sensing performance of the conductive composite material. Fig. 7k illustrates the schematic diagram of the recovery process of the conductivity of the AgNWs/Te–Te–PDMS composite. These results demonstrated that the rapid self-healing properties of the elastic substrate promote efficient functional recovery in sensor devices, potentially enhancing material longevity and contributing to environmental sustainability.

Fig. 7 The self-healing behaviour of AgNWs/Te–Te–PDMS composites. (a)–(c) Digital photographs for the self-healing process of the AgNWs/Te–Te–PDMS composite connected to a circuit with LED bulbs. (d) Digital photograph of the damaged conductive composite material being repaired under xenon lamp illumination. (e–g) Optical micrographs of the AgNWs/Te–Te–PDMS composite in original, damaged and healed condition. (h) Electrical resistivity (ρ) of the original and damaged composite after the first and second cutting–healing cycles. The ECG curves measured using the (i) original and (j) healed samples as the sensing electrodes. (k) Schematic illustrations for the self-healing process of the AgNWs/Te–Te–PDMS composite.

3. Conclusions

In summary, a series of Te–Te–PDMS elastomers exhibiting exceptional mechanical robustness and rapid photoactivated self-repair were engineered through the synergistic integration of dual dynamic networks: hydrogen-bonded motifs and ditelluride covalent linkages. The successful formation of these supramolecular architectures was confirmed through comprehensive spectroscopic analyses (¹H NMR, FT-IR, and XPS) coupled with UV-vis absorption studies. Crucially, harnessing the unique photoresponsivity of ditelluride bonds, the elastomers demonstrated remarkable healing efficiencies under UV light (98% recovery within 30 minutes) and xenon lamp irradiation (97% recovery within 60 minutes). Mechanistic studies employing in situ EPR spectroscopy and quantitative computational modelling elucidated a radical-mediated exchange process governing the light-triggered bond reorganisation. Building upon these material properties, AgNWs were integrated into the Te–Te–PDMS matrix to fabricate conductive polymer composites. These multifunctional materials exhibited dual utility as strain sensors for biomechanical monitoring and dry epidermal electrodes capable of clinical-grade electrophysiological signal acquisition (ECG/EMG). This work not only depicts a novel strategy for wavelength-selective photoactivated self-healing systems via dynamic ditelluride bond engineering, but also substantially enriches the field of dynamic chemistry.

Author contributions

Mingfeng Dai: conceptualization, methodology, and writing original draft. Xiang Han: data curation and investigation. He Zhang: software and visualization. Jing Yan: validation and investigation. Ruipeng Han: resources. Longkun Que: formal analysis. Yifan Guo: conceptualization. Zuowan Zhou: supervision, project administration, and writing – review & editing.

Conflicts of interest

There are no conflicts of interest to declare.

Data availability

The data supporting this article have been included as part of the ESI.†

Acknowledgements

Financial support from the Sichuan Provincial Science and Technology Planning Project (Grant No. 2020YFN0150 and 2020ZDZX0016) is gratefully acknowledged. The authors also extend their appreciation to Ms Yanzhou Lei of the Analytical and Testing Centre, Southwest Jiaotong University, for her expert assistance in transmission electron microscopy (TEM) characterisation.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d5mh00655d

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