We next measured the photophysical properties of all three compounds in an OLED-relevant nonpolar host (4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP)) at different weight concentrations ranging from 2 to 10 wt% (Figure ). The 2 wt% doped CBP films of TPAPyAP, TPAPyBP and TPAPyBPN emit at λPL of 537, 560 and 585 nm, respectively, corresponding to the emission in dilute toluene solutions. The ΦPL of the 2 wt% CBP doped films of TPAPyAP TPAPyBP and TPAPyBPN are 62, 60 and 62%, respectively (Table ). As the doping concentration increased, all compounds showed a red-shifted emission accompanied by a decrease in ΦPL. While the 10 wt% TPAPyBPN doped film in CBP exhibited a more pronounced red-shifted emission at λPL of 605 nm and a high ΦPL of 56%; thus, this doping concentration was chosen for the following characterization studies. As shown in Figure , all three compounds show unstructured ICTbased emission at room temperature. Similar to that observed in toluene at 77 K, the prompt fluorescence of 2 wt% TPAPyAP, TPAPyBP and TPAPyBPN doped in CBP film at 77 K are structureless, with associated S1 energies of 2.50, 2.33 and 2.23 eV, respectively. As expected, the phosphorescence spectra of all three compounds are structured, with T1 values of 2.18, 2.18 and 2.17 eV, matching well with the TDA-DFT calculations as a mixed 3 LE/ICT state. The ΔEST of these films of TPAPyAP, TPAPyBP and TPAPyBPN are 0.32 eV, 0.15 and 0.06 eV, respectively (Figure ). As shown in Figure , TPAPyBP and TPAPyBPN each showed multiexponential decay kinetics at room temperature, with average prompt fluorescence lifetimes, tp, of 10.0 ns and 15.0 ns, respectively (Figure ), and average delayed emission lifetimes, td, of 2.3 ms and 2.1 ms, respectively. The relative intensity of the delayed PL increases with increasing temperature from 100 K to 300 K for both compounds, thereby corroborating the TADF nature of the emission of these three compounds in the CBP films. However, TPAPyAP showed monoexponential decay kinetics with a fluorescence lifetime of 8.4 ns (Figure ), which can be explained by the large ΔEST and inefficient TADF in the doped CBP film. We also explored the photophysical properties of the three emitters in a higher polarity host, PPT (Figure ). TPAPyBPN exhibited the most red-shifted emission of 53 nm compared to that in TPAPyAP (42 nm) and TPAPyAP (48 nm). The larger red-shift in TPAPyBPN can be attributed to it having the largest dipole moment of 5.7 D. The ΦPL values of TPAPyAP, TPAPyBP and TPAPyBPN doped in nonpolar CBP are 62, 60 and 62%, respectively, and they remain high, at 75, 63 and 60 %, in polar PPT, respectively in 2 wt% doped films (Table ). As shown in Figure , the doped PPT films of TPAPyAP, TPAPyBP and TPAPyBPN all show multiexponential decay kinetics with average tp of 6.8 ns, 9.7 ns, and 14.0 ns and average td of 1.4 ms, 0.68 ms and 0.11 ms at room temperature, respectively. Temperature-dependent time-resolved PL decays evidence the TADF nature of the emission in the PPT doped films (Figure ). The S1 levels of TPAPyAP, TPAPyBP and TPAPyBPN are stabilized modestly from 2. 48