We next measured the time-resolved PL decay of 4PXZPh-[10]CPP in solvents of different polarity. In non-polar solvent of hexane, 4PXZPh-[10]CPP exhibit a prompt lifetime (τp) of 4.4 ns, while in more polar solvents such as toluene (PhMe), DCM, tetrahydrofuran (THF), the τp values increase to 11.0, 14.5, and 13.6 ns, respectively. In the polar solvent DMF, the τp reduces to 3.1 ns. However, no delayed emission is observed in any of the solvents within a time window of 2 µs. The S1 and T1 energies of 4PXZPh-[10]CPP were determined in both PhMe and DCM in 77 K. As shown in Figure , derived from the onset of the prompt fluorescence, the S1 of 4PXZPh-[10]CPP in DCM is stabilized to 2.75 eV compared to 2.93 eV in PhMe, which led to a smaller ΔEST of 0.50 eV in DCM than 0.68 eV in PhMe as the T1 is 2.25 eV in both solvents. More importantly, as the molecular relaxation is suppressed at low temperature, 4PXZPh-[10]CPP shows a pronounced red-shifted PL in DCM at room temperature, which will lead to a smaller ΔEST than that determined in the glass state. However, compared to the TD-DFT predicted excited-state energies (S1: 2.65 eV, T1: 2.57 eV), the T1 measured in both toluene and DCM are strongly stabilized while the S1 measured in toluene and DCM are stabilized by 0.28 eV and 0.10 eV, respectively, and this leads to a much larger experimentally determined ΔEST, which prohibits RISC from readily occurring at room temperature. = 907.8 ns (Figure ). The temperature dependence of the transient PL decay in all doped PyD2, PPF and CzSi films were performed from 300 K to 200 K. However, the delayed emission component in these films exhibited a decrease with decreasing temperature, which implies that the emission is not TADF.