Researchers from the University of Michigan at Ann Arbor and the University of Illinois at Urbana-Champaign have developed a class of dendrimer molecules that "harvest" light. The molecules have a unique, treelike structure that enables them to collect light energy. Light is trapped in the dendrimer's "branches" and is funneled down in the form of energy packets called excitons. Losing a small amount of energy at each branching point, the light is trapped in a central part of the molecule. Another property of the dendrimer is its resistance to photobleaching. Scientists hope this molecule could lead to microscopic optical sensors that change color when exposed to trace chemicals, tiny molecular lights that illuminate the DNA of living cells, and organic molecules that convert sunlight into energy. The funding for this project comes from the National Science Foundation and the Office of Naval Research.