Zwitterionic locking of spiropyran-based block copolymer self-assembly

This study explores the role of zwitterionic interactions in the self-assembly behavior of block copolymers containing polydimethylsiloxane (PDMS) and spiropyran (SP) in response to reversible UV-induced isomerization from SP to merocyanine (MC). This alters the polarity and rigidity of the self-assembled copolymer, modulating intermolecular interactions among the copolymer blocks. The self-assembly behavior of SP- and MC-containing block copolymers was investigated in both solution and bulk states, highlighting interactions among zwitterionic MC units. Notably, the relaxation kinetics of MC-to-SP ring closure were highly sensitive to the medium, as confirmed via UV–vis spectroscopy. Structural reorganization following photoisomerization was characterized via dynamic light scattering, atomic force microscopy, and small-angle X-ray scattering, revealing changes in polymer aggregate size and domain spacing, attributable to strong zwitterionic interactions in both solution and bulk. These findings demonstrate the role of photoinduced zwitterionic interactions in block copolymer self-assembly and provide insights into the design of photoresponsive polymeric materials.