Exploiting an ingenious combination of photochemical (i.e., light-induced) reactions and self-assembly processes, a team led by Prof. Alberto Credi of the University of Bologna has succeeded in inserting a filiform molecule into the cavity of a ring-shaped molecule, according to a high-energy geometry that is not possible at thermodynamic equilibrium. In other words, light makes it possible to create a molecular "fit" that would otherwise be inaccessible.