New molecular pairs for low power non-coherent triplet-triplet annihilation based upconversion: dependence on the triplet energies of sensitizer and emitter

►Green to violet upconversion, based on a triplet-triplet annihilation process. ► Upconversion involving a porphyrin, an aromatic hydrocarbon, and incoherent light. ► Unusual energetically hindered and entropically driven upconversion phenomenon. ► Effect of concentrations of sensitizer and emitter on the upconversion intensity. ► Role of the triplet energies of the molecular pair.