With these results at hand, we investigated the TTA-UC performance of the different systems. The concentrations employed for UC measurements were 25 µM of 4CzBN and 10 mM (1 mM for 2PI and TIPS-Naph, vide infra) of the annihilator, resulting in systems with endothermic TET (i.e., TET from 4CzBN to PPD) also having FTET close to 89% (as calculated by Equation S4). Delayed UC fluorescence could be observed from all systems upon 405 nm excitation, and the UC emission spectra of TIPS-Naph and TP are presented in Figure .