Synthesis and characterization of an expanded antiaromatic macrocycle porphyrin analogue

Abstract

Expansion of porphyrin-like macrocycles can provide insights into the relationship between structural, optical, and electronic features. Here, we report the synthesis of a new nominally antiaromatic expanded porphyrin-like macrocycle (6) prepared via the condensation of 1,4-bis-(3,4-diethyl-2-pyrryl)benzene dialdehyde (4) with hydrazine. The absorption and emission features of this new macrocycle were compared to those of the parent bipyrrole-derived macrocycle, a system first reported in 1997. Attempts to oxidize both macrocycles (5 and 6) were unsuccessful, a failure ascribed to the steric limitations imposed by two substituents present on the [Formula: see text]-positions on the di-substituted pyrrolic precursor. This stands in contrast to what was observed for the original bipyrrole system bearing only a single [Formula: see text]-substituent on each of the pyrrolic moieties. The present results underscore the possible role of structure in governing electronic transitions in expanded porphyrins while highlighting the facility of hydrazine-based condensations in accessing readily large pyrrolic macrocycles.