Investigation of Intramolecular Triplet–Triplet Annihilation Upconversion by Double Sensitization

Intramolecular triplet-triplet annihilation upconversion (TTU) using dimers composed of two anthracene units has distinct advantages over intermolecular TTU, as it can enable upconversion even in diluted states. However, clear evidence of the occurrence of intramolecular TTU remains insufficient. In this study, we focus on the double-sensitization mechanism, which is caused by double triplet energy transfer from triplet sensitizers to the dimers. It is a phenomenon inherent in intramolecular TTU. We provide direct evidence of intramolecular TTU by investigating the dependence of the TTU phenomenon on dimer concentration under conditions where the double-sensitization mechanism is dominant.