Synthesis of Expanded Crowned Macrocycles Containing Two Pyrrolo[1,2‐a]indole Units

Abstract

AbstractExpanded crowned macrocycles containing two pyrrolo[1,2‐a]indole moieties in their macrocyclic framework have been synthesized by condensing a 1,4‐bis(2‐thienyl) benzene‐based diol with three different crown based tripyrranes under acid‐catalyzed conditions. HRMS and NMR studies were used to deduce the molecular structures of fused expanded crowned macrocycles. The studies indicated the occurrence of two intramolecular fusions between two core pyrrolic nitrogens with carbon atoms of two phenylene groups to generate two pyrrolo[1,2‐a]indole moieties as a part of expanded porphyrin framework. DFT studies indicated that the macrocycles are highly nonplanar and adopt a trapezoidal structure. The absorption spectral studies showed that the macrocycles exhibit three bands in 350–520 nm region and electrochemical studies indicated the electron‐rich nature of the macrocycles. Furthermore, the expanded crowned macrocycles form stable cation radicals upon treatment with trifluoroacetic acid as judged from absorption, electron spin resonance studies, and the cation radicals that formed absorb strongly in the NIR region. TD‐DFT studies corroborate with the experimental observations.