(401 nm) and 1.1 × 10 4 M -1 cm -1 (388 nm). The tendency of the ε values match the TDA-DFT results where the oscillator strengths (f) reduce from 0.37 for 4CzPyz to 0.22 and 0.05 for 3CzBPz and 2CzBPz, respectively. The three compounds exhibit structureless emission in toluene with λPL of 473 nm, 450 nm, and 440 nm for 4CzPyz, 3CzBPz, and 2CzBPz, respectively. The blue-shifted emission of 3CzBPz, and 2CzBPz are ascribed to the weaker character of the acceptors. The three emitters exhibit a moderately high ΦPL in degassed toluene, of 71%, 65%, and 64% for 4CzPyz, 3CzBPz, and 2CzBPz, respectively, which are slightly reduced to 66%, 63%, and 61% after exposure to oxygen. The S1 and T1 values were extracted from the onsets of the fluorescence and phosphorescence spectra, respectively, in 2-methyltetrahydrofuran (2-MeTHF) glass at 77 K (Figure The time-resolved PL decays of these materials were measured in 10 -5 M degassed toluene solution (Figure ). 4CzPyz, 3CzBPz, and 2CzBPz exhibit prompt lifetime (τp) of 6. The smaller degree of red-shifting of the emission spectra and smaller µe in 2CzBPz suggest that there is greater LE character to the S1 state in this compound than in 3CzBPz and 4CzPyz. With a view to using these compounds as emitters in OLEDs, we then investigated the photophysics of the three emitters in solid-state matrices. The photoluminescence spectra of three emitters are insensitive to the medium, with λPL of 486 nm, 463 nm, and 446 nm for 4CzPyz, 3CzBPz and 2CzBPz (Figure ), which are only modestly red-shifted compared to the corresponding λPL of 473 nm, 450 nm, and 440 nm in toluene, respectively. The highest ΦPL value for 4CzPyz was achieved in 10 wt% doped PPT film at 75%, which is significantly higher than the 36% previously reported in the 10 wt% doped DPEPO film. The ΦPL values for 3CzBPz and 2CzBPz in PPT are 56%, and 38%, respectively, which are slightly lower than corresponding values in DPEPO (Figure ). The tendency of the ΦPL of the three emitters match the TDA-DFT calculated trend in oscillator strength. The three emitters in 10 wt% doped PPT films exhibit unstructured emission, with FWHM of 64 nm, 63 nm and 44 nm for 4CzPyz, 3CzBPz and 2CzBPz, respectively, and the phosphorescence is of dominant CT character with broader (FWHM ~ 120 nm) and featureless emission (Figure ). The calculated ΔEST values of the three emitters determined from the onsets of the prompt fluorescence and phosphorescence spectra, are 0.23 eV (same value as previously reported in DPEPO), 24 0.29 eV, and 0.34 eV for 4CzPyz, 3CzBPz and 2CzBPz (Figure ), respectively.