The behavior of Cz-CO-PTZSO 2 is different. The steady-state PL spectra in air and vacuum at 298 K are similar (l PL = 440 nm) (Figure ), with a PL lifetime of 0.7 ns (Figure ). Although dual RTP behavior was recorded, it differs from that of Cz-C-PTZSO 2 . The blue RTP emission band from Cz-Ph is absent in Cz-CO-PTZSO 2 , but a new structured RTP emission band is present at l PL of 572 nm. At 80 K, the phosphorescence emission blue-shifts to the green emission range, whose low-temperature LTP lifetime is 89.8 ms (Figure ). We assigned dual phosphorescence to originating from dual emission from the monomer and the aggregates, which is consistent with both the theoretical calculations and the recorded PL spectra. The computed hole-electron distribution analysis revealed that the phosphorescence of Cz-CO-PTZSO 2 results from LE T 1 emission from Cz-BP (Figure ). Therefore, we measured the phosphorescence spectrum of Cz-BP at 77 K (Figure ), which coincides with the green RTP emission band of Cz-CO-PTZSO 2 . We can therefore assign this band to phosphorescence from the Cz-BP moiety. To determine the origin of the orange RTP emission, we collected RTP spectra at various delay times. The results revealed that RTP at 520 nm decays much faster than the RTP at 572 nm (Figure ), with corresponding t Ph of 12.3 ms and 244.3 ms, respectively (Figure ). By closer inspection of the phosphorescence spectra of dilute samples in 2-MeTHF glass at 77 K, we found that the RTP emission centered at 572 nm vanished (Figure ), implying that the lower-energy RTP of Cz-CO-PTZSO 2 originates from molecular aggregates. As a result, we can conclude that dual phosphorescence of Cz-CO-PTZSO 2 belongs to the mixture of T 1 emission of monomer and aggregates. The F PL values of Cz-C-PTZSO 2 and Cz-CO-PTZSO 2 at 298 K in air are 5.9% and 4.6%, respectively, which improve to 8.2% and 4.7% under a N 2 atmosphere, respectively (Table ). Therefore, the calculated RTP F PL values of Cz-C-PTZSO 2 and Cz-CO-PTZSO 2 in N 2 are approximately 4% and 0.1%, respectively (Figure ). The weaker RTP of Cz-CO-PTZSO 2 may be caused by the presence of increased nonradiative channels. Figure shows the RTP afterglows of Cz-C-PTZSO 2 and Cz-CO-PTZSO 2 in vacuum. Further, temperature-dependent PL measurements were conducted to interrogate the origin of the multiple phosphorescence. For Cz-C-PTZSO 2 , the apparent blue-shift of the phosphorescence emission occurs as the temperature decreases (Figure ), indicating that phosphorescence from Cz-Ph gradually dominates the spectral profile. At 80 K, compared to the phosphorescence spectra of Cz-Ph and PTZSO 2 (Figures and), blue-shifted and structured phosphorescence spectra at different time-gated windows was observed, which further confirmed that phosphorescence from T 1 and T 2 of Cz-C-PTZSO 2 are dominated by LE emission from Cz-Ph and PTZSO 2 (Figure ), respectively; the T 1 and T 2 energies, estimated from the emission peaks, are 2.36 eV and 2.64 eV, respectively. The related Commission Internationale de l¢Éclairage (CIE) diagram reflects the gradual emission color change across different time-gated windows (Figure ). The images of Cz-C-PTZSO 2 also evidence that the afterglow gradually varies from green to blue (Figure ). A similar scenario was observed in Cz-CO-PTZSO 2 , where temperature-dependent phosphorescence blue-shifts as a function of decreasing temperature (Figure ). However, at 80 K, phosphorescence from Cz-BP dominates the emission, independent of the time-gated window. The CIE diagram and images of afterglows document the unchanged phosphorescence color (Figures and Next, the photophysical properties of the Cz-C-TRZ and Cz-CO-TRZ crystals were investigated.