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

A tetra-functionalized pyrene precursor 4b is prepared using the Suzuki-Miyaura coupling of 1,3,6,8-tetrabromopyrene with N -Boc-2-pyrroleboronic acid. 4b displayed a blue emission with a high quantum yield (ϕ F = 0.89). 4b is subjected to [3 + 2] Lewis acid-catalyzed condensation with 2,2'-bithiophene-dialcohol 5 , affording a planar bis-N 2 S 2 internally linked with pyrene. The single-crystal X-ray structure of bis-N 2 S 2 revealed a planar conformation with all of the pyrrolic nitrogens and thiophenic sulfurs pointing toward the macrocyclic core. Further, the reduction of bis-N 2 S 2 was attempted in the presence of Zn/NH 4 Cl at room temperature in CHCl 3 . A sharp color change from pink to brown was observed presumably due to the formation of its reduced congener bis-N 2 S 2 - 2H . However, the reduced species was found to revert back to its oxidized form over a period of 25 min in CHCl 3 . Density functional theory (DFT) studies reveal that the two monocyclic halves of bis-N 2 S 2 -2H 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 bis-N 2 S 2 - 2H was confirmed by High-resolution/mass spectrometry (HR/MS) analysis. Experimental and theoretical studies reveal a weak aromatic character of bis-N 2 S 2 due to the absence of global conjugation.