Optimized Cz dimers: Stg, syn, and anti conformations
Before we discuss the relative stabilities of optimized dimers, we first briefly compared the calculation data in this study and experimental values in the literature,[8] for the singlet (E(S1)) and triplet (E(T1)) excited state energies, and their difference, ΔEST, of the Cz monomer; see Table 1. As reported previously,[15, 36-37] the data in Table 1 clearly show that all the methodologies in this test consistently overestimate E(S1) and E(T1) compared to experiments; the calculated E(S1) and E(T1) are ca. 0.38~0.49 eV and ca. 0.15~0.40 eV higher than the experimental values, respectively. However, their energy differences, ΔEST, are computed to be ca. 0.06 to 0.31 eV higher, meaning that the singlet and triplet excitation energy were calculated in a reasonably balanced way. We most importantly note that the SOS-CIS(D0)/aDZ calculation level yields the best values compared to the experimental data in the literature; the differences between the calculated values at this level and experimental data are ca. 0.38, 0.32, and 0.06 eV, for the E(S1), E(T1), and ΔEST, respectively. Thus, the stabilities of Cz dimers are judged mainly by the energy values derived at this level of theory.
Table 1. Adiabatic excitation energies (in eV) for the lowest-lying singlet (S1) and triplet (T1) states, and their difference of carbazole moleculea