Reentrant phase transition via light–heat antagonism in a single polymer system

Abstract

Inspired by nature's reliance on antagonistic interactions to orchestrate complex dynamics, synthetic systems often replicate this by integrating multiple competing components—a strategy frequently hampered by synthetic complexity and kinetic mismatch. Here, we report a single-component spiropyran-functionalized polymer system that exhibits programmable reentrant phase transitions mediated by light–heat antagonism in reversible spiropyran isomerization. Within this system, light and heat competitively drive the interconversion of spiropyran between its ring-closed SP⁻ and ring-opened MCH forms, allowing precise modulation of intermolecular electrostatic interactions and thereby enabling real-time control over polymer conformation and phase transitions. Following this principle, we demonstrate versatile reversible switching of a single polymer system among nonthermoresponsive, monothermoresponsive (UCST-type), and reentrant thermoresponsive states—the latter displaying LCST behavior at low temperatures and UCST behavior at high temperatures. This light–heat regulatory mechanism is further extended to hydrogels, where it enables programmable reentrant volumetric transitions and autonomous oscillatory deformation. By employing noninvasive light to flexibly tailor multimode responsiveness in a single system, our work establishes a robust and generalizable platform for dynamically programmable matter with prospects in soft robotics and biomedicine.