Design and Development of Donor-Acceptor Stenhouse Adducts: A New Visible Light Activated Photochromic Compound
The development of an easily synthesized, modular, and tunable organic photoswitch that responds to visible light has been a long-standing pursuit. Herein we provide a detailed account of the design and synthesis of a new class of photochromes based on furfural, termed donor−acceptor Stenhouse adducts (DASAs). A wide variety of these derivatives are easily prepared from commercially available starting materials, and their photophysical properties are shown to be dependent on the substituents of the push−pull system. Analysis of the switching behavior provides conditions to access the two structural isomers of the DASAs, reversibly switch between them, and use their unique solubility behavior to provide dynamic phase-transfer materials. Overall, these negative photochromes respond to visible light and heat and display an unprecedented level of structural modularity and tunabilty. We demonstrate the considerable potential of DASA photoswitches in two unique and powerful applications. First we have applied DASAs for the visible light-initiated recycling of homo-geneous organic catalysts. This catalyst-photoswitch construct effectively polymerized lac-tide with control over molecular weight and a low PDI. The visible-light mediated phase transfer and subsequent recovery of the thiourea catalyst allowed recycling of the organocat-alyst. Further, the potential of these photoswitches in biological applications is demonstrated through the synthesis of a functional amphiphile that displays on-demand light-mediated disassembly and cargo release. This one-photon visible light-responsive micellar system served as an efficient, on-demand drug delivery system. The efficiency and effectiveness of this system was demonstrated in an in-vitro setting, delivering the chemotherapeutic paclitaxel only on exposure to visible light.