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

• Published in: Journal of organic chemistry Vol. 87; no. 22; pp. 15022 - 15030
• Main Authors: Ipe, Ruth Mariam, Nag, Probal, Mori, Shigeki, Nambiar, Anjana P., Vennapusa, Sivaranjana Reddy, Gokulnath, Sabapathi
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 18.11.2022; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Organic; Crystallography, X-Ray; Mass Spectrometry; Molecular Conformation; Physical Sciences; Pyrenes; Science & Technology; COMPLEX; PYRENE; PHOTOPHYSICAL PROPERTIES; PORPHYRIN
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/acs.joc.2c01362

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 (ϕF = 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/NH4Cl at room temperature in CHCl3. 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 CHCl3. 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.