Tetracene Dimers: A Platform for Intramolecular Down- and Up-conversion

Photon energy conversion can be accomplished in manydifferentways, including the two opposing manners, down-conversion (i.e., singletfission, SF) and up-conversion (i.e., triplet-triplet annihilationup-conversion, TTA-UC). Both processes have the potential to helpovercome the detailed balance limit of single-junction solar cells.Tetracene, in which the energies of the lowest singlet excited stateand twice the triplet excited state are comparable, exhibits bothdown- and up-conversion. Here, we have designed meta-diethynylphenylene- and 1,3-diethynyladamantyl-linked tetracenedimers, which feature different electronic coupling, to characterizethe interplay between intramolecular SF (intra-SF) and intramolecularTTA-UC (intra-TTA-UC) via steady-state and time-resolved absorptionand fluorescence spectroscopy. Furthermore, we have used Pd-phthalocyanineas a sensitizer to enable intra-TTA-UC in the two dimers via indirectphotoexcitation in the near-infrared part of the solar spectrum. Thework is rounded off by temperature-dependent measurements, which outlinekey aspects of how thermal effects impact intra-SF and intra-TTA-UCin different dimers.