where [ : 𝐸𝑚𝑖 * ] < is the initial concentration of triplet state of the emitter after the TET reaction. A maximum value of 𝛷 ((# is 0.5 (50 %), indicates that two triplet-excitons are converted into one singlet exciton. TTA is a bimolecular reaction whereby two tripletexcitons collide. Hence the longer the lifetime of the triplet-exciton and the faster the TTA reaction rate of the triplet-excitons, the higher the 𝛷 ((# becomes. A common approach to prolong 𝜏 ( is to control the molecular structure to suppress nonradiative deactivation processes and excimer formation processes . For example, 9,10-diphenylanthracene (DPA), which is used as an TTA emitter in the TTA-UC systems, has very long 𝜏 ( , over 1 ms , and achieves high 𝛷 ((# . On the other hand, molecular design focusing to improve the 𝑘 ((# is also important but has not been paid significant attention. When we only consider intramolecular TTA , we do not need to discuss diffusion rate because the collisions between chromophore molecules are not needed for TTA. However, molecular diffusion is often required for several practical TTA-UC applications in fluid environments.