Photoswitchable Liquid‐to‐Solid Transition of Azobenzene‐Decorated Polysiloxanes

Having external control over fundamental properties of polymers, such as their physical state, is a crucial yet challenging design criterion for smart materials. Liquifying polymers through photochemical events has significantly advanced various research lines. However, the opposite process solidifying polymer that intrinsically in liquid state reversibly with light unattained. Herein, light-controlled liquid-to-solid transition polysiloxanes reported, which are decorated small number azobenzene-functionalized ureidopyrimidinone (Azo-UPy) pendants. The UPy moieties toggle between intra- and intermolecular hydrogen bonding via trans→cis photoisomerization azobenzene. This transformation on molecular level leads to formation strong supramolecular cross-links, which, turn, results macroscopic solidification material. photoswitching event enables post-synthetic tailoring polymers’ mechanical properties, thus providing an alternative addition plasticizers or hardeners. Moreover, adhesion strength photochromic material increases by factor 6 upon exposure UV light. In situ illumination during rheological measurements reveals delicate interplay wavelength dependent penetration depth efficiency. conceptually new (de)bonding demand strategy paves way creating light-responsive materials exciting applications temporal adhesion, recycling, lithography, processing.