The steady-state PL (SS PL) and phosphorescence (Ph) spectra were measured in 2methyltetrahydrofuran (2-MeTHF) at 77 K to determine the singlet and triplet energies and, thus, the ΔEST values of the four emitters (Figure ). The singlet and triplet energies were determined from the onsets of the SS PL and Ph spectra, respectively. The S1/T1 energies for tCzBT1B (2.57/2.50 eV) and tCzBT2B (2.57/2.51 eV) are close to those of the corresponding states of BTC-BNCz (2.59/2.48 eV, measured in frozen toluene), whereas for tDPABT1B and tDPABT2B the S1/T1 energies are slightly destabilized at 2.64/2.51 eV and 2.66/2.52 eV, respectively. The moderately small ΔEST values (<0.14 eV) of the four emitters are consistent with the SCS-ADC2 calculated values. The transient PL (TR PL) decays of tDPABT1B and tDPABT2B show monoexponential kinetics, with prompt lifetimes (τp) of 3.8 and 3.9 ns, respectively, while there is no delayed emission observed in toluene. By contrast, the TR PL decays of tCzBT1B, and tCzBT2B show biexponential kinetics, with τp of 3. We next investigated the photophysical properties of tCzBT1B, and tCzBT2B in PhCzBCz, as this host was used with BTC-BNCz in the literature report. We investigated tDPABT1B and tDPABT2B, compounds that have higher excited-state energies, in 2,6-DCzPPy as this host as it has a better alignment of its S1/T1 energies (3.35/2.88 eV) than PhCzBCz (3.31/2.95 eV) to induce more efficient energy transfer from host to emitter; further, it has greater bipolar carrier transport ability. Based on the concentration screen, the highest ΦPL for tCzBT1B (85%) and tCzBT2B (88%) were obtained as 4 wt% doped films in PhCzBCz, with λPL of 492 nm for both emitters. The reported photophysics for the 3 wt% doped film of BTC-BNCz in PhCzBCz is comparable (λPL of 488 nm and ΦPL of 95%). For tDPABT1B and tDPABT2B, the highest ΦPL, 68 and 70%, espectively, are achieved as 4 wt% doped films in 2,6-DCzPPy films, with λPL of 478 and 477 nm, respectively; moderately improved compared