Photoswitchable NHC-promoted ring-opening polymerizations

The UV-induced photocyclization of a dithienylethene-annulated N-heterocyclic carbene precatalyst enabled photoswitchable ring-opening polymerizations of e-caprolactone and δ-valerolactone. The polymerizations proceeded efficiently in ambient light, however UV irradiation attenuated the reaction rate (kamb/kUV = 59). Subsequent visible light exposure reversed the photocyclization and restored catalytic activity.