Advances in Functional Photoisomerisable Low-Molecular-Weight π-Gelators

Abstract

Functional photoresponsive π-gelators represent the new generation of low-molecular-weight gelators (LMWGs) that self-assemble through noncovalent interactions, including hydrogen bonding, π–π stacking, and van der Waals forces. Photoresponsive gelators incorporate photochromic groups that reversibly restructure upon light irradiation, offering tunability of the gel–sol phase transitions. This responsiveness provides an external control over the gel behavior with non-invasive stimuli such as light, UV, or visible light, making them interesting candidates for sensors, optomechanical actuators, environmental remediation, controlled drug delivery, and adaptive materials. Photoisomerisable π-gelators are an important type of photoresponsive gelators. Azobenzene, stilbene, and cinnamate are suitable photochromic moieties, which can switch between trans–cis isomerization, when exposed to certain wavelengths of light to exhibit photoisomerisation. This review provides a critical assessment of the design principles, structural characteristics, mechanisms, and sol-gel behavior of low molecular weight gelators in response to UV–Vis light irradiation, as well as their potential applications. We have also outlined future directions for developing next-generation photoisomerisable gelators as programmable, light-controlled materials.