So-called cooperative behavior, in which molecules in a crystal change their structure in concert with one another, is common in biological molecules and metals. Such behavior, however, is rare in molecular crystals, and scientists don’t quite understand why. Now researchers using the Advanced Photon Source (APS), a U.S. Department of Energy Office of Science user facility at Argonne National Laboratory have found they can induce cooperative behavior in an organic semiconductor and have developed an explanation for why it happens.