The HOMO-LUMO transition in 1B-CzCrs is purely SRCT, while in 2B-CzCrs it exhibits more of LRCT character, which is reflected in the lower oscillator strength (f) in the latter. Analysis of the excited-state difference density plots confirmed that the SRCT S1 state in 1B-CzCrs is extended over more of the compound compared to 2B-CzCrs. The nature of the T1 state in both molecules is essentially the same as the respective S1 states, yielding comparable ΔEST in both molecules. More notably, there are significant differences in the nature of the T2 state, with T2 of 1B-CzCrs having more of a LE character on the carbazole moiety, while that of 2B-CzCrs still retains SRCT character, similar to that of S1 state. This results in a considerably higher spin-orbit coupling (SOC) value in 1B-CzCrs compared to that in 2B-CzCrs. (Fig. ). The ΔEST was estimated from the difference in the onsets of the fluorescence and phosphorescence spectra after applying the Jacobian conversion at 0.21 and 0.24 eV for 1B-CzCrs and 2B-CzCrs, respectively (Fig. ). These values agree well with the theoretical ones calculated at the SCS-ADC(2)/cc-pVDZ level of theory (0.16 and 0.17 eV, respectively). The ΦPL values of 1B-CzCrs and 2B-CzCrs in the air are 63 and 55%, respectively, and these significantly increased to 96 and 94% under N2. This indicates the large contribution of triplets to their light-emitting process. The high ΦPL values can be attributed to their highly rigid structure, resulting in reduced nonradiative decay. However, only a short decay lifetime component was observed in the transient PL for both 1B-CzCrs and 2B-CzCrs in toluene (Figs. and). This is because, despite the high FPL, non-radiative decay competes with RISC. The lifetime slightly increases under N2, indicating that oxygen may affect the singlet radiative decay rates. a ΦPL were measured using an integrating sphere at λexc = 310 nm under N2-saturated and aerated (in parentheses) conditions. b τp was measured with a streak camera under N2-saturated and aerated (in parentheses) conditions at λexc = 355 nm. c Estimated from the onset wavelength of the steady-state PL spectrum at 77 K. d Estimated from the onset wavelength of the delayed emission spectrum (115-150 ms) at 77 K (λexc = 310 nm). e Rate constants were calculated using the reported method in the literature under the approximation of no phosphorescence contributed to the delayed emission.