Low-power sensitized upconversion by way of triplet-triplet annihilation (TTA-UC) is a broadly useful process that enables the conversion of optical light into photons of higher energy. Unlike other upconverting processes such as second harmonic generation or two-photon absorption, TTA-UC makes it possible to upconvert light that is not monochromatic even at low power densities. These characteristics are ideal for a variety of applications that range from the optimization of photovoltaic devices to bio-imaging. While TTA-UC had been known to occur in solution for some 50 years, it was - by members of our team - only recently achieved in solid polymers. Building on this breakthrough, our program seeks to unravel the parameters that govern the TTA-UC process in solid materials, with the objective to create a basis for the rational design of upconverting materials with ultimate properties.  While the original work in the group focused on the preparation of upconverting elastomeric films, our current research focuses on the development of polymeric and molecular upconverting glasses. In parallel, we are developing a series of molecular probes and architecturally defined molecules and macromolecules to investigate the influence of confinement and connectivity on energy transfer and particularly on the triplet-triplet annihilation step.