Fabrication of Soft Submicrospheres by Sequential Boronate Esterification and Their Dynamic Behavior

Pyridine‐assisted sequential boronate esterification of benzene‐1,4‐diboronic acid and 1,2,4,5‐tetrahydroxybenzene has induced hierarchical molecular self‐assembly, and in turn producing well‐defined submicrospheres. Spectroscopic analyses such as FE‐SEM, TEM, DLS, NMR, XRD, and IR absorption spectroscopy indicates that the particles are composed of lamellar structures of sp 2 ‐hybridized trigonal planar poly(dioxaborole). The spontaneous self‐organization is ascribable to reactive layer‐by‐layer assembly through sequential boronate esterification of the diboronic acid and the tetrahydroxybenzene whereby initially formed oligo(dioxaborole) may provide a platform for further reactions, thus resulting in the production of submicrospheres. It is interesting to note that the dynamic covalent functionality as a result of the dioxaborole linkage induced a stimuli‐responsive change in morphology by not only a pH switch but also the exchange reaction with pentaerythritol. Further, a selective saccharide‐induced change in the submicrosphere morphology was observed through a simple exchange reaction of dynamic covalent boronate esters with saccharides in THF; the selective change in morphology is visually detected through the color change in the solution. These findings can provide a useful insight into the design of stimuli‐responsive hierarchical architectures based on boron‐containing dynamic covalent bond.