Light‐Responsive Shape: From Micrometer‐Long Nanocylinders to Compact Particles in Electrostatic Self‐Assembly

A light‐triggered shape change of supramolecular nanostructures is achieved through electrostatically self‐assembly of linear polyelectrolytes and oppositely charged dyes in aqueous solution: Upon UV‐irradiation, 1‐µm‐long, flexible cylinders with a cross‐section of 10 nm convert into ellipsoids of 400 nm × 40 nm. The nano‐object shape is encoded in the molecular dye structure. A shape transition upon irradiation can occur for electrostatically self‐assembled nanoparticles. Defined and tunable nanoparticle shapes emerge from linear flexible polyelectrolytes and ionic dyes in aqueous solution—promising for solar to mechanical energy conversion.