Synthesis, Redox Properties and Structural Features of Expanded Isophlorins

The expanded derivatives of isophlorin provide sufficient examples for Huckel’s 4nπ anti-aromatic systems. They vary significantly in their electrochemical properties compared to the aromatic expanded porphyrins. In comparison to the small macrocycles, the large and planar expanded isophlorins exhibit reversible two-electron oxidation. The structure of these macrocycles also undergo reversible structural transformation between planar and figure of eight conformations accompanying the redox process. The oxidized product could be identified as aromatic dication or as a polaron pair depending on the size of the macrocycle. The number of non-pyrrolic heterocyclic units is crucial to stabilize aromatic, antiaromatic or neutral radical isophlorin. A stable 25π neutral radical identified in a one-pot synthesis, exhibits reversible one electron redox to form 24π anti-aromatic cation and a 26π aromatic anion. Synthesis, experimental details and structural features of expanded isophlorins will be highlighted in this presentation.

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