Light and Dark Cycles Control the Structural Evolution of Photoresponsive Supramolecular Systems.

As the supply of light on Earth is cyclic and asymmetric, living systems that rely on photochemical energy have adapted to accommodate periods of light and darkness. During the day, light energy is available, while throughout the dark phases, thermal relaxation processes can be used to increase functional and structural organization. While light-driven supramolecular assembly has been reported, structural adaptation under alternating light/dark input remains largely unexplored in synthetic supramolecular systems. Here, we show how an oscillating light energy supply can facilitate the structural selection of self-assembling photoswitchable peptides compared to continuous illumination. We demonstrate that polymorphic self-assembled structures are transiently formed and sustained only under light irradiation, while alternating periods of irradiation and darkness favor the formation of a thermodynamically more stable supramolecular architecture. These findings demonstrate the key role that rest (darkness) periods can have in the self-assembly pathway selection of molecular and self-organized supramolecular photosystems.