Visible Light-Responsive Microgels Modified with Donor–Acceptor Stenhouse Adducts

Donor–acceptor Stenhouse adducts (DASAs) as T-type organic photochromic molecules have recently attracted a lot of attention because of their negative photochromic and versatile synthesis. Herein, we synthesized for the first time a series of novel visible light- and temperature-responsive poly(N-vinylcaprolactam) microgels decorated by DASA molecules via a robust and straightforward post-modification synthesis route that allows covalent attachment of DASA molecules via the epoxy groups present in the microgel structure. The synthesized microgels exhibit homogeneous distributions and temperature responsiveness in aqueous solutions. The photoswitching behaviors of the microgels in different solvents [water, toluene, dichloromethane (DCM), and tetrahydrofuran (THF)] were systematically investigated. The fabricated microgels demonstrate an irreversible photoswitching behavior in water and toluene. Contrarily, reversible photoswitching behaviors of the microgels in DCM and THF were observed. The size of the microgels in aqueous solutions can be modulated by visible light irradiation. Additionally, the microgels were employed as carriers to undergo a visible light-triggered release of fluorescent dye, suggesting their applicability for the photostimulated delivery of hydrophobic drugs.