We next turned our attention to the photophysical characterization in an OLED-relevant host matrix, 1,3-bis(N-carbazolyl)benzene (mCP) as it has a suitably high triplet energy (E T = 3.0 eV). The mCP matrix can also contribute to the suppression of non-radiative processes in the emitters, and host-guest interactions can also regulate triplet vibronic coupling and energies. We first studied the steadystate PL behavior of the two emitters in mCP at various doping concentrations (Figure ). As doping concentration increases from 1 wt% to 10 wt%, there is only a 10 nm red-shift of the PL in PhCz-O-DiKTa, while in PhCz-DiKTa there is a slightly larger 20 nm spectral red-shift. This study reveals that there is very little aggregation at these doping concentrations as suggested by the absence of strong intermolecular interactions in the crystal structures. A remarkable enhancement in the F PL values of 80% and 91% for PhCz-O-DikTa and PhCz-DiKTa in N 2, respectively, was recorded at 10 wt% doping compared to those at 1 wt% (F PL < 55%) and 5 wt% (F PL < 70%) doping (Table ). Thus, 10 wt% emitter-doped mCP films were selected for further photophysical measurements. The corresponding photophysical data are summarized in Tables and. Similar spectral profiles of the steady-state (SSPL), prompt, and delayed emissions were recorded in PhCz-O-DikTa and PhCz-DiKTa, with the SSPL maxima, l PL , of ~ 500 nm and ~ 525 nm (Figures and), respectively; the FWHMs of PhCz-O-DikTa and PhCz-DiKTa are 57 nm and 72 nm, respectively. The spectral FWHM broadening probably results from the enhanced electronic coupling from interactions of dimeric species in addition to host-guest interactions compared to the emission of isolated monomers (Figure ). Multiexponential decay kinetics were observed, with prompt fluorescence lifetimes, t P , for PhCz-O-DikTa and PhCz-DiKTa of 8.0 ns and 10.1 ns (Figure ), respectively, and delayed fluorescence lifetimes, t DF , of 653.5 µs and 103.8 µs in vacuum (Figure ), respectively. Temperaturedependent transient PL decay behavior revealed that both compounds are TADF emitters (Figure ).