Bis-subporphyrin-like boron( <scp>iii</scp> ) complexes derived from indolo[2,3- <i>a</i> ]carbazole-based cyclic bis-BODIPYs exhibiting persistent helical chirality

Herein, we report the synthesis of 11,12-dihydroindolo[2,3-<i>a</i>]carbazole (InC) 1 incorporating expanded porphyrinoid 8, and its boron(iii) complexes (8·BF₂ and 8·BF). These macrocycles exhibit a 'figure-eight' conformation that exists as a pair of helical enantiomers (<i>P</i>,<i>P</i> and <i>M</i>,<i>M</i>), confirmed by X-ray crystallographic analysis. The 'figure-eight' structures are stabilized by intramolecular hydrogen bonds such as NH⋯N and NH⋯F interactions. The synthesized macrocycles demonstrate excellent stability under ambient conditions. Further, the helically-locked structure 8·BF exhibited closely held InC units with a distance of 6.17 Å and enabled facile optical resolution using chiral HPLC. Circular dichroism spectroscopy of enantiopure 8·BF shows the Cotton effect at 692 nm extending to the near-IR region with Δ<i>ε</i> up to 150 M^-1 cm^-1. The chiral induction of racemic macrocycle 8 was employed using enantiopure mandelic acids.