Doubly dithieno[3,2-b:2',3'-d]thiophene-fused planar core-modified heptaphyrin: Unusual synthesis, spectral and computational studies

A doubly DTT-fused, core-modified 30π nearly planar heptaphyrin is reported herein. The synthesis involves a TFA-catalyzed oxidative coupling reaction, followed by DDQ-mediated oxidation. Serendipitously, in addition to the 34π doubly fused octaphyrin, the heptaphyrin was obtained in trace amounts. The formation of the heptaphyrin was confirmed by ESI mass spectrometric analysis. UV–Vis spectroscopy, along with Δδ values obtained from 1 H NMR spectroscopy, confirms the Hückel aromatic nature of the macrocycle in both its free-base and protonated forms. Furthermore, theoretical calculations were performed on the molecule, and geometry-optimized structures revealed distinct conformational features. These computational results are consistent with the spectroscopic data, further supporting the aromatic character of the macrocycle in both its free-base and protonated states.