Phenanthrene-Incorporated Isoamethyrin: A Near-Planar Macrocycle That Display Enhanced Aromaticity via Protonation-Triggered Conformation Changes

Controlling the aromaticity in expanded porphyrins isa forefrontresearch topic, and the strategy of using protonation-triggered conformationalchanges to fine-tune electronic properties and aromaticity has yetto be generalized in rigid and planar expanded porphyrins. Here, we synthesized phenanthrene-incorporated isoamethyrins that possessnear-planar conformations and nonaromatic characters. However, whenmethanesulfonic acid (MSA) was added, geometric deformations occurredto minimize the unfavorable strain, resulting in macrocycles thatwere weakly aromatic as a whole.