Promoting the Furan Ring-Opening Reaction to Access New Donor-Acceptor Stenhouse Adducts with Hexafluoroisopropanol.

Donor-acceptor Stenhouse adducts (DASAs) are visible-light-responsive photoswitches with a variety of emerging applications in photoresponsive materials. Their two-step modular synthesis, centered on the nucleophilic ring opening of an activated furan, makes DASAs readily accessible. However, the use of less reactive donors or acceptors renders the process slow and low yielding, which has limited their development. We demonstrate here that 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) promotes the ring-opening reaction and stabilizes the open isomer, allowing greatly reduced reaction times and increased yields for known derivatives. In addition, it provides access to previously unattainable DASA-based photoswitches and DASA-polymer conjugates. The role of HFIP and the photochromic properties of a set of new DASAs is probed using a combination of 1 H NMR and UV/Vis spectroscopy. The use of sterically hindered, electron-poor amines enabled the dark equilibrium to be decoupled from closed-isomer half-lives for the first time.