Photoacid-Induced Supramolecular Network Disassembly: A Systems Approach to Stimuli-Responsive Polymers

The introduction of supramolecular (SM) motifs allows the design of stimuli-responsive polymers whose physical properties can be changed by external triggers that affect the SM binding. However, using this approach to create light-responsive materials that can be switched under isothermal conditions proves to be challenging. Here, we report a material systems approach to achieve this. Thus, SM polymer networks, in which optically inert ureidopyrimidinone (UPy) groups assemble into reversible cross-links, are combined with a trigger molecule, the photoacid generator (PAG) 2-(4-methoxy-styryl)-4,6-bis(trichloromethyl)-1,3,5-triazine (MBTT). Model experiments with a fluorescent, self-reporting UPy motif elucidate the sequence of processes that result from optical triggering, namely acid generation, protonation of UPy groups, and ultimately dissociation of the SM cross-links. The optically stimulated transformation of gels and rubbery films into viscous liquids was quantitatively monitored by opto-rheological measurements, showing that the optical stimulation and resultant mechanical responses are intimately coupled. The potential usefulness of this approach to create materials with spatially graded mechanical characteristics and as the basis for debonding-on-demand (DOD) adhesives was explored in proof-of-concept experiments.