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Typical cross-linked polymer networks have rubbery elasticity and do not exhibit thermoplasticity such as linear polymers. However, thermodynamically cross-linked polymer networks exhibit certain t...

The magical fantasy of decades-old transformer characters is becoming closer to scientific reality, as transformable materials can change their shapes in response to thermal, mechanical, electrical, and chemical stimuli. However, precise and prompt control of plastic shaping remains to be wanted. Photoresponsive materials provide a promising alternative for rapid optomechanical shaping with limited success. Here, we report a new class of photoplastic transformation based on dynamic covalently crosslinked polytriazole (PTA) networks, in which crosslinking points are comprised of photocleaveable hexaarylbiimidazole (HABI). Upon sub-500 nm light irradiation, HABI is dissociated into two triphenylimidazole radicals (TPIRs) followed by spontaneous recombination back to the initial state. This photoswitching effect is demonstrated to generate nonthermal shape change in the PTA-HABI gel network at will upon light stimulus. A unique photoalignment phenomenon has also been discovered which can form oriented nanoscale patterning in the PTA-HABI gel network upon laser irradiation. The solvent-free PTA-HABI elastomer exhibits photoenhanced automatic self-healing properties at temperatures ranging from 25 °C to freezing points, which is attributed to the dynamic equilibrium between TPIRs and HABI. A photoplastic spring is fabricated and exhibits photoswitchable plastic behavior, i.e., a reversible transformation between plastic strain and elastic strain upon light irradiation. HABI-based polymer networks, including solvated gel and solvent-free elastomer, are promising as smart materials for nonthermal photoactivated shape changing, transformation, and self-healing applications.

Photo-driven hydrogel actuators have attracted tremendous attention due to their underwater photo-mechanical applications, but these critical limitations include reliance on harmful UV light, slow driving speed and limited transformation morphologies need to be further resolved. Here, the transparent polyurethane (PU) hydrogels containing dual networks of dynamic covalent crosslinked hexaarylbiimidazole (HABI) and permanent-crosslinked pentaerythritol units are fabricated and exhibit diversified anisotropic transformations in response to visible light. The underwater three-dimensional (3D) actuations including curling, twisting and folding can be spatiotemporally programmed and achieved within tens of seconds. The biomimetic flower and hydrogel wheel enable rapid photo-driven locomotion. The hydrogel actuators possess great fatigue resistance and reusability. Our work provides new insights to the design of underwater biomimetic intelligent actuators based on photochemically transformation.