Answers are grounded in this paper and cite their sources.
Light out of darkness? Most sensitizers for triplet–triplet annihilation (TTA) upconversion are strongly phosphorescent. A new RuII–coumarin dyad, on the other hand, has a non-emissive 3IL excited state (ΦP=0.2 %) but shows a good upconversion quantum yield (ΦUC=2.7 %, see picture, TTET=triplet–triplet energy transfer).
No takes yet. Share an insight, caveat, or question.
Ji et al. (2011) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: