Fig. 3. (a) Computed mechanism of the photoisomerization [6]2− → [10]2− and free energies of intermediates and transition states in their S0 states. The energetically unfavorable and thus photochemically conducted step [6]2− → [Int1]2− is marked in red. (b) Literature-reported intermediates of the photoisomerization of triptycene 6C and their calculated free energies (this work). (c) and (d) Known boratanorcaradienes K[12] and Na[14] obtained from photoreactions of tetraarylborates K[11] and Na[13], respectively. Carbon atoms marked with asterisks bear t-Bu substituents.
