Shining light on cyclopentadienone–norbornadiene Diels-Alder adducts to enable photoinduced click chemistry with cyclopentadiene

A new Diels−Alder (DA)-based photopatterning platform is presented, which exploits the irreversible, light-induced decarbonylation and subsequent cleavage of cyclopentadienone−norbornadiene (CPD−NBD) adducts. A series of CPD−NBD adducts have been prepared and systematically studied toward the use in a polymeric material photopatterning platform. By incorporating an optimized CPD−NBD adduct into polymer networks, it is demonstrated that cyclopentadiene may be unveiled upon 365 nm irradiation and subsequently clicked to a variety of maleimides with spatial control under mild reaction conditions and with fast kinetics. Unlike currently available photoinduced Diels−Alder reactions that rely on trapping transient, photocaged dienes, this platform introduces a persistent, yet highly reactive diene after irradiation, enabling the use of photosensitive species such as cyanine dyes to be patterned. To highlight the potential use of this platform in a variety of material applications, we demonstrate two proof-of-concepts: patterned conjugation of multiple dyes into apolyacrylate network and preprogrammed ligation of streptavidin into poly(ethylene glycol) hydrogels.