At 77 K, the lPL of the steady-state PL spectrum of the 10 wt% doped film of TPPQ in CBP is 578 nm, while the delayed emission spectrum peaks at λPh of 775 nm (Figure ). The corresponding S1 and T1 energies are 2.50 and 1.88 eV, thus the DEST is 0.62 eV. The phosphorescence of TPPQ in CBP closely resembles that in glassy MCH, indicating that it occurs from the same 3 LE state. The S1 and T1 energies of the 10 wt% doped film of 4DMAC-TPPQ in CBP are 2.23 and 1.94 eV, while those of the 5 wt% doped film of 4PXZ-TPPQ in CBP are 2.07 and 1.92 eV (Figure ). The corresponding DEST for 4DMAC-TPPQ is 0.29 eV, and 0.15 eV for 4PXZ-TPPQ. Given that the T1 state energy remains effectively the same for the same LE state, the smaller DEST values for the three emitters in CBP are due to the stabilization of the S1 state. In comparison to doped film (5 wt%), the S1 energy of the neat film of 4PXZ-TPPQ is significantly red shifted at 1.85 eV (∆S1 = 0.25 eV), while the neat film of 4DMAC-TPPQ showed small red-shift at 2.12 eV (∆S1 = 0.11 eV) in comparison to the doped film of 10 wt% 4DMAC-TPPQ in CBP, however, the T1 energies of the neat films of both emitters are similarly red-shifted. The ∆EST of neat 4PXZ-TPPQ is significantly smaller at 0.04 eV, while ∆EST of neat 4DMAC-TPPQ is the same as the doped film, at 0.29 eV (Figures and, Table ). Such a large declines of S1 energy and ∆EST of a neat film 4PXZ-TPPQ in comparison to doped films could be explained by the synergistic effect of the transformation of exciton states due to the formation of aggregates and shortening intermolecular distance because of planar phenoxazine motifs, which induce π-π interactions between adjacent molecules in neat film 4PXZ-TPPQ compared with doped film. As expected, no delayed emission was observed in the 10 wt% doped film of TPPQ in CBP and the emission decays with biexponential kinetics, with an average lifetime, τPL of 42.8 ns at 300 K. By contrast, the 10 wt% doped film of 4DMAC-TPPQ and 5 wt% doped film of 4PXZ-TPPQ in CBP show multiexponential decay kinetics, with average prompt lifetime, τp of 25.2 and 17.6 ns, while average delayed lifetime (τd) are 564.5 and 303.9 μs at λPL of 635 and 680 nm, respectively at 300 K (Figure ). The corresponding estimated kRISC and kISC of the 10 wt% 4DMAC-TPPQ in CBP is 1.32 ´ 10 3 and 2.00 ´ 10 7 s -1 which slightly increase to 2.48 ´ 10 3 and 3.17 ´ 10 7 s -1 for the 5 wt% doped 4PXZ-TPPQ in CBP, respectively (Table ). On the other hand, the τp of the neat film of 4DMAC-TPPQ is 27.2 ns and the τd is 109.4 μs, while the τp and τd for the neat film of 4PXZ-TPPQ are much shorter at 3.7 ns and 2.05 μs, respectively. Therefore, the kRISC of the neat film of 4PXZ-TPPQ significantly increased (4.9 ´ 10 5 s -1 ) in comparison to the neat film of 4DMAC-TPPQ (5.03 ´ 10 3 s -1 ) which is strongly aligned with the reduced ΔEST of neat 4PXZ-TPPQ. The temperature-dependent time-resolved PL decay studies of both emitters indicate that these compounds are TADF active not only in doped films but also as their aggregates (Figures and).