Fig. 4. FMOs (a) and state energy diagrams (b) of compounds biA1a–d computed at the rCAM-B3LYP/cc-pVDZ level. Molecular orbitals similar with the (Hückel) biA1 model distribution (left) marked with green checkmarks, otherwise marked with red crosses. Red ovals in structures biA1c and biA1d indicate steric hindrance.
