[2 + 2] Photocycloaddition Reaction Regulated the Stability and Morphology of Hydrogels

Photoresponsive supramolecular gels as intelligent non-invasive responsive materials can undergo changes in color, state, morphology and electronic properties upon photo irradiation, making them attractive for a variety of applications. Herein, a novel supramolecular hydrogelator DBE with 1,4-divinylbenzene as the central core, connected via amide linkage to l-phenylalanine and peripheral hydrophilic groups, was designed to evaluate the effect of [2 + 2] photocycloaddition reaction on supramolecular hydrogels. UV irradiation decreases the solubility of the hydrogelator DBE and hence, causes the destruction of the gel. SEM images clearly show that irradiation with UV light could induce disintegration of the right-handed helical nanofibers entangled network, which turns into nanoparticles and eventually massive crystals. Circular dichroism and vibrational circular dichroism data also indicate the formation of right-handed helical nanofibers in DBE gel. FTIR and MALDI–TOF–MS spectrum confirm that the variation of stability and aggregated morphology of DBE gel after UV irradiation is attributed to [2 + 2] cycloaddition reaction of vinyl units. This study presents a wonderful model for regulating the stability and aggregated morphology of supramolecular hydrogels via photo irradiation, as well as offers new ideas for designing novel photo responsive materials.