Reversibly Slowing Dewetting of Conjugated Polymers by Light

Dewetting, i.e., the retraction of a fluid from a surface it "dislikes", is a macroscopic phenomenon controlled through parameters like viscosity and surface tension on length-scales much larger than the size of the molecules. So far, dewetting was known to proceed in the same manner, independent of the dewetting film being illuminated by light or not, e.g., through an optical microscope. Here, we demonstrate that the velocity of dewetting of conjugated polymers can be reversibly tuned through appropriate exposure to light. We relate this observation to the absorption of photons of suitable energy resulting in the generation of excitons which may partially delocalize along and across polymer chains and so induce changes in polymer chain conformation. Such changes, in turn, may cause stiffening or overlap of polymer chains and thus lead to macroscopically detectable differences in behavior of an ensemble of conjugated molecules expressed via material properties like viscosity.