Synthesis, Structure, and Optical Properties of a Bis-Macrocycle Derived from a Highly Emissive 1,3,6,8-Tetra(1-pyrrol-2-yl)pyrene.

A tetra-functionalized pyrene precursor is prepared using the Suzuki-Miyaura coupling of 1,3,6,8-tetrabromopyrene with -Boc-2-pyrroleboronic acid. displayed a blue emission with a high quantum yield (ϕ = 0.89). is subjected to [3 + 2] Lewis acid-catalyzed condensation with 2,2'-bithiophene-dialcohol , affording a planar internally linked with pyrene. The single-crystal X-ray structure of revealed a planar conformation with all of the pyrrolic nitrogens and thiophenic sulfurs pointing toward the macrocyclic core. Further, the reduction of was attempted in the presence of Zn/NHCl at room temperature in CHCl. A sharp color change from pink to brown was observed presumably due to the formation of its reduced congener -. However, the reduced species was found to revert back to its oxidized form over a period of 25 min in CHCl. Density functional theory (DFT) studies reveal that the two monocyclic halves of exhibit differences in aromaticity depending on amino and imino pyrroles present inside each individual core. Such a conversion was also monitored by ultraviolet-visible (UV-vis) absorption spectral studies, and the exact composition of - was confirmed by High-resolution/mass spectrometry (HR/MS) analysis. Experimental and theoretical studies reveal a weak aromatic character of due to the absence of global conjugation.