Executive SummaryThe research performed during the period of Award DE-FG02-01ER15270 was dedicated to achieving an improved understanding of artificial solar light-harvesting molecules. These organic molecules may be components of low-cost solar energy systems.We were interested in a particular class of such molecules, multibranched dendrimers, which can mimic the light-harvesting function of the biological light-harvesting complex.The dendrimers investigated were composed of a phenylene ethynylene (PE) framework which had previously been shown to exhibit very high energy harvesting efficiencies.Using both theoretical and experimental methods, we found that the energy-containing excited states in these conjugated networks begin as localized states, but quickly undergo a limited delocalization to a new state which determines the energy transfer rate. By achieving an improved understanding of the fundamental photophysics of PE dendrimers, we are now in a position to evaluate their potential as light-harvesting components of lowcost solar cells. In addition, we also demonstrated the phenomenon of exciton fission in a single covalent molecule for the first time. Exciton fission represents a way to double (in principle) the yield of electron-hole pairs generated by solar photons, and thus represents a way to significantly increase the efficiency of organic solar cells. Both accomplishments 1