where Φ %&" , ΦTTEnT, and ΦTTA, are the efficiencies of ISC of the photosensitizer, TTEnT from the photosensitizer to the annihilator, and TTA of the annihilator, respectively, while ΦF is the fluorescence quantum yield of the annihilator. 49, The parameter 𝑓 is the spin statistical factor, which relates to the probability that (S1) is formed upon TTA, and ½ is due to the fact that one high-energy photon is emitted upon absorption of two low-energy photons during TTA-UC.