Phototropic self-growing hydrogels based on a tricyanofuran derivatized photoswitch

Phototropism is ubiquitous in plants that endows them directional movement and substantial growth toward light sources. Simultaneous replication of such phototropic movement and volumetric growth in synthetic polymers is important but currently remains challenging. Here, we report the molecular design of a photoswitchable tricyanofuran (TCF) based hydrogel that can concurrently display such phototropic movement and self-growth in water under stimulation of light and pH. The macroscale growth of the hdyrogel originates directly from the molecular charge rise of the TCF switch upon isomerization induced by light or pH, which dramatically improves the polymer hydrophilicity and facilicates water diffusion into the network. As the growing rate under each stimulation is independently regulated, we successfully developed TCF hydrogels displaying heterogeneous growth accompanied with phototropic bending deformation by taking the advantage of the differential growing rates induced by light and pH. Importantly, the phototropic deformation direction during the growing process can be flexibly switched to be either positive or negative by tuning the light irradiation and pH conditions for applications in replicating the structure and function of natural light-responsive systems. Our work provides a novel molecular design strategy for advancing the development of biomimetic systems with capability of phototropic deformation and self-growth.