Nevertheless, the TDA-DFT calculations did predict the nature of the T1 states correctly, with T1 state of DMAC-TPI being localised on TPI, while that of PXZ-TPI being of mixed CT/LE character. PTZ-TPI showed very weak fluorescence yet intense phosphorescence in frozen toluene matrix at 77K. This phosphorescence is dominated by triplet emission from PTZ, as the spectrum aligns with that of PTZ in Zeonex at room temperature (Figure ). The DEST of PTZ-TPI is thus of a similar magnitude to that of PTZ (0.62 eV vs 0.53 eV) and is significantly smaller than in the other two compounds (each at ~1.2 eV). As both the singlet and triplet excited states are localized on the PTZ, spin-orbit coupling is not possible according to El Sayed's rule and thus no exciton upconversion is likely to occur.