Then, emission from aggregates dominates the overall RTP emission, accompanied by a small contribution from the TRZ phosphorescence at around 500 nm. The RTP afterglow color of Cz-C-TRZ varies from blue to orange (Figure ). Temperature-dependent phosphorescence measurements also documented that multiple emissive triplet states exist in Cz-C-TRZ (Figure ). At 80 K, LTP emission negligibly changes with time (Figure ), reflected by the observed unchanged LTP afterglow (Figure ). To further confirm that the orange RTP is from aggregates, we prepared Cz-C-TRZ crystals via slow sublimation, which we hypothesized would leave samples with increased p-p stacking. These samples of Cz-C-TRZ show stronger orange RTP and negligible blue RTP (Figures and) due to aggregates. The RTP lifetime and RTP F PL of Cz-C-TRZ crystals acquired via temperature gradient vacuum sublimation increase to 540.3 ms and 3.0% (Figure , Table ), respectively, compared to the respective values of the Cz-C-TRZ crystals (t ph = 190.7 ms, RTP F PL = 0.6%) isolated from toluene. At 80 K, green LTP from TRZ centered at 500 nm was also observed likely due to the suppression of nonradiative processes (Figure ), whose lifetime is prolonged to 820.8 ms (Figure ). For Cz-CO-TRZ, steady-state PL spectra show an unstructured emission centered at 486 nm at room temperature (Figure ), whose overall F PL and lifetime in air are 13.9% and 2.4 ns, respectively (Table , Figure ). Unfortunately, no RTP was observed, probably resulting from strong nonradiative decay. A broad and structured LTP profile was recorded at 80 K (Figure ). Time-gated PL measurements reflect that the LTP results from LE emission contributions from each of Cz-Ph, Cz-BP, and TRZ (Figure ) based on the cross-comparison with the LTP from each of these isolated compounds (Figures and). The low-temperature multiple phosphorescence bands may result from restricted molecular conformations lead to weak electronic coupling at low temperature.