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 lotof attention because of their negative photochromic and versatilesynthesis. Herein, we synthesized for thefirst time a series of novelvisible light- and temperature-responsive poly(N-vinylcaprolactam)microgels decorated by DASA molecules via a robust andstraightforward post-modification synthesis route that allowscovalent attachment of DASA molecules via the epoxy groupspresent in the microgel structure. The synthesized microgelsexhibit homogeneous distributions and temperature responsivenessin aqueous solutions. The photoswitching behaviors of themicrogels in different solvents [water, toluene, dichloromethane (DCM), and tetrahydrofuran (THF)] were systematicallyinvestigated. 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 aqueoussolutions can be modulated by visible light irradiation. Additionally, the microgels were employed as carriers to undergo a visiblelight-triggered release offluorescent dye, suggesting their applicability for the photostimulated delivery of hydrophobic drugs.