This alignment of the state energies suggests that the emission of 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB originates from the emitting DtBuCzB core. The S1/T1 energies of 2GtBuCzCN and tBuCzCN are 3.20/2.97 eV and 3.34/2.98 eV (Figure ), respectively, measured under the same conditions, with corresponding DEST of 0.23 and 0.36 eV. This implies that kRISC in 2GtBuCzCN will be faster than in tBuCzCN and thus the former will be a much more efficient exciton harvester, reflected in their respective diverging τd of 80.4 µs and 1.1 ms (Figure ). The S1/T1 energies and DEST of tBuCzCN is also almost identical to those of tBuCzCO2H (3.39/3.02 eV and 0.37 eV, Figure ), thus leading to both compounds having similar τd of 0.9 ms (Figure ), values that are similar to that in toluene. The higher energies of these states than those of DtBuCzB explains the origin of the efficient FRET between the two within 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB. In addition, 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB have higher FPL of 71 and 56% than DtBuCzB With a vision for using these emitters in OLEDs, we next investigated the photophysical properties in mCP, which was identified as the best host material because of its suitably aligned HOMO/LUMO energy levels with the adjacent layers in the OLED stack (vide infra), its high triplet energy (3.0 eV), and the high-quality and homogeneous films that could be prepared by spin-coating. Benefitting from the "encapsuled" nature of their structures, the PL of both 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB showed a resistance to concentration quenching (Figure as the doping concentration increased from 1 to 70 wt% in mCP films, no excimer emission was observed. Impressively, the narrowband emission of 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB observed in the 1 wt% doped film in PMMA is conserved in the 70 wt% doped films, with lPL/FWHM of 496/31 and 499/29 nm, respectively (Figure ). The highest FPL values were achieved at 30 wt% doping at 94 and 98% for 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB, respectively, at this doping level, the lPL/FWHM are 492/27 and 495/26 nm (Figure ). Similarly, in these films 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB also maintain their small DEST of 0.14 and 0.15 eV, respectively (Figure ). The average prompt, tp, and delayed, td, lifetimes are 7.0 ns and 101.8 µs for 2GtBuCzCO2HDCzB and 6.4 ns and 143 µs for tBuCzCO2HDCzB. The corresponding kISC are 8.57×10 7 and 7.81×10 7 s -1 and kRISC are 2.37 ×10 4 and 1.23×10 4 s -1 for 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB, respectively, which are faster than the kRISC in PMMA doped film, which can be attributed to different host-guest interactions that affect the DEST of the emitter. .