Substituent Effects on Shape-Memory and Photoisomerization in β-Cyclodextrin–Azobenzene Composite Gels

The integration of photochromic and shape-memory functionalities into a single polymer system offers innovative opportunities for the development of multifunctional smart materials that can sense, respond to, and adapt to external stimuli. In this study, we designed dual-responsive supramolecular organogels by incorporating methacrylate-functionalized azobenzene derivatives with electron-donating (azobenzene-OMe, ABOMe) or electron-withdrawing (azobenzene-NO 2, ABNO 2 ) substituents as guest molecules, together with acrylated β-cyclodextrin (β-CD) as the host unit. Stable organogels were obtained by combining tetra(ethylene glycol) diacrylate (TTEGDA), β-CD, and either ABOMe or ABNO 2, thereby yielding composite gels (CG) designated ABOMe-CG and ABNO 2 -CG, respectively. These gels were subsequently evaluated to determine how substituent electronics influence their mechanical, thermal, and photoresponsive behaviors. Rheological analysis, UV–vis spectroscopy, and variable-temperature/light 1 H NMR revealed that ABOMe-CG exhibited stronger host–guest interactions, leading to enhanced gel stiffness, efficient and reversible E – Z photoisomerization, and robust shape-memory recovery. Conversely, ABNO 2 -CG, incorporating the electron-withdrawing nitro group, exhibited weaker host–guest complexation, reduced mechanical stiffness, and diminished responsiveness to both thermal and optical stimuli. These findings underscore the critical influence of electronic substituents in modulating supramolecular assembly and emergent material properties. By systematically tuning molecular interactions at the host–guest interface, this study offers a rational design strategy for engineering soft materials with integrated optical and mechanical responsiveness. The resulting gels hold significant promise for advanced applications such as soft actuators, reconfigurable devices, adaptive sensors, and stimuli-responsive drug delivery systems.