Light-Gated Amine Exchange in Diarylethene-Crosslinked Microgels

The functionalization of microgels with photoswitchable moieties enables the construction of multi-responsive systems, which are highly interesting for biological applications, for example, in drug delivery. Controlling the reversible uptake of functional molecules, however, remains a major challenge. To address this, we developed a novel aniline-type diarylethene (DAE) crosslinker and prepared a series of corresponding poly(N-vinylcaprolactam)-based microgels with varying degrees of DAE crosslinker. Upon UV light irradiation, the aniline (and thus enamine) motif of the DAE is converted to its imine form, thus allowing for reversible exchange with primary amines. Irradiating the DAE with blue light covalently locks the equilibrium and traps the amine in the microgels. The light-controlled covalent binding of fluorinated, hydrophobic, and hydrophilic amine derivatives was proven by dynamic light scattering and 19F NMR spectroscopy. Importantly, the impact of photoisomerization and amine binding on microgel properties was investigated and we were able to remotely control size as well as temperature and pH responsiveness by light. Overall, this study demonstrates optically gated uptake and release of functional amines in multi-responsive microgels and highlights their potential biological applications.