Photoinduced Strain‐Assisted Synthesis of a Stiff‐Stilbene Polymer by Ring‐Opening Metathesis Polymerization

Developing a novel strategy to synthesize photoresponsive polymers is of significance owing to their potential applications. We report a photoinduced strain‐assisted synthesis of main‐chain stiff‐stilbene polymers by using ring‐opening metathesis polymerization (ROMP), activating a macrocyclic π‐bond connected to a stiff‐stilbene photoswitch through a linker. Since the linker acts as an external constraint, the photoisomerization to the E‐form leads to the stiff‐stilbene being strained and thus reactive to ROMP. The photoisomerization of Z‐form to E‐form was investigated using time‐dependent NMR studies and UV/Vis spectroscopy. The DFT calculation showed that the E‐form was less stable due to a lack of planarity. By the internal strain developed due to the linker constraint through photoisomerization, the E‐form underwent ROMP by a second generation Grubbs catalyst. In contrast, Z‐form did not undergo polymerization under similar conditions. The MALDI‐TOF spectrum of E‐form after polymerization showed the presence of oligomers of >5.2 kDa.