Mechanochemical Fluorescence Switching in Polymers Containing Dithiomaleimide Moieties

Polymers that display useful mechanochemical responses, such as changes of their fluorescence characteristics, are attracting great interest. Here, we introduce the fluorescent dithiomaleimide (DTM) motif as a mechanofluorophore and report the mechanoresponse of two polymer types containing this motif. Poly(methyl acrylate) (PMA) and poly(ε-caprolactone)s (PCL) featuring one DTM moiety in the center of each chain (PMA-DTM and PCL-DTM) were synthesized by controlled radical and coordination-insertion ring-opening polymerizations using bifunctional DTM-containing initiators. Upon ultrasonic treatment of PMA-DTM or PCL-DTM of sufficiently high initial molecular weight, both the molecular weight and the fluorescence intensity decreased with similar kinetics, while no significant fluorescence changes were observed for DTM-free reference polymers. The results show that the DTM motif can serve as a mechanophore that displays a mechanically induced fluorescence turn-off.