The excited-state properties were calculated using time-dependent density functional theory (TD-DFT) within the Tamm-Dancoff approximation (TDA-DFT) based on the optimized ground-state geometries . The S1/T1 energy levels are 2.05 / 1.82 eV for T-tBuCz-AQ which decreases to 1.81 / 1.62 eV for T-MeOCz-AQ. These energy levels for C-tBuCz-AQ and C-MeOCz-AQ are further stabilized to 1.88 / 1.79 eV and 1.68 / 1.51 eV respectively. However, in the case of tBuCz-PA and DMAC-PA, the S1/T1 energy levels are found to be 2.27 / 2.11 eV and 1.79/ 1.77 eV respectively (Table ). The calculated ∆EST values are in the range of 0.19-0.23 eV. Natural transition orbital (NTO) analysis of T-tBuCz-AQ reveals that both the S1 and T1 state particles are located on the tBuCz donors while the holes are localized on the anthraquinone, illustrating its CT character (Table ). Similar NTO distributions were noted for the S1 and T1 states of T-MeOCz-AQ, while for C-tBuCz-AQ and C-MeOCz-AQ, the hole is located on one of the two Cz donors and the particle is localized on the anthraquinone, indicating CT character of these states. Similar hole and particle localizations on donor (Cz/ DMAC) and anthraquinone were noted for tBuCz-PA and DMAC-PA. The spin-orbit coupling matrix elements (SOCME) between S1 and T1 at the optimized S1 geometry of T-tBuCz-AQ (<S1|ĤSOC|T1> = 0.07 cm -1 ) and C-tBuCz-AQ (<S1|ĤSOC|T1> = 0.06 cm -1 ) are larger than those of T-MeOCz-AQ (<S1|ĤSOC|T1> = 0.02 cm -1 ) and C-MeOCz-AQ (<S1|ĤSOC|T1> = 0.001 cm -1 ), despite similar NTOs for all four compounds; a similar trend in SOCME values between S1 and T2 was also observed (Table ). For tBuCz-PA and DMAC-PA, the hole and particle are localized on the donor (tBuCz/ DMAC) and pyrazoloanthrone, respectively, in both S1 and T1 states, implying their CT character. However, as both the hole and particle in the T2 are localized on the pyrazoloanthrone this state has LE character. As a result, the SOCME values between S1 and T2 are much larger than between S1 and T1 for tBuCz-PA and DMAC-PA (Table ).