We present an unusual upconversion process based on the sensitized tripletatriplet annihilation where the triplet energy of the donor exceeds that of the acceptor. Either a palladium octaethyl-porphyrin (PdOEP) or a platinum octaethyl-porphyrin (PtOEP) are the sensitizers, whereas tetraphenyl-pyrene (TPPy) is the emitter. The two couples convert the green to violet light in deoxygenated toluene with different efficiencies. The quantum yields of the upconversion processes (IBBUC) were calculated at different concentrations and intensities. We focused on low power non-coherent irradiation to simulate the solar energy supply. To demonstrate the important role played by the rate of the energy transfer from sensitizer to emitter in optimizing IBBUC, we tested the effect of the substitution of TPPy with 9,10-diphenylanthracene.