Two photoswitchable arylazopyrozoles form hydrogels at a concentration of 1.2 % (w/v). With molecular weight 258.28 g mol?1, these are the lowest known hydrogelators that respond reversibly to light. Photoswitching E- Z-form by exposure 365 nm light results in macroscopic gel?sol transition; nearly an order magnitude reduction measured elastic and loss moduli. In case meta-arylazopyrozole, cryo...