Photo-Reversibility of Cinnamylidene Acetic Acid Derived Crosslinks in Poly(ε-caprolactone) Networks


Photoswitchable polymeric materials comprise moieties that undergo light-induced chemical reactions or conformational alteration. The reversibility of photo-responsive molecular switches has an influence on material functions observed on the macroscopic level such as reversibility of shape switching, especially with regard to the number of cycles. Cinnamylidene acetic acid (CAA) has received attention due to its reversible dimerization by [2+2] cycloaddition reactions. In the present study, possible side-reactions during photo-scission of the CAA dimers as netpoints in poly(ε-caprolactone) based materials were studied by fluorescence spectroscopy, HPLC and 1H,1H-COSY. Liberation of fluorescent fragments, which have their origin in the various dimer structures, could only be found in small amounts, while a non-identified species seems to be generated during dimerization and photo-scission. The results furthermore suggest that CAA-based switches in PCL-networks do not provide full reversibility of netpoint formation under the examined conditions, due to non-selective side-reactions, which could lead to an attenuation of the macroscopic effect in multiple photo-cycles. In perspective, the design of CAA derivatives with enhanced photo-reversibility should be targeted.
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