Synthesis and Studies of Pyrene-Embedded Stable Nonaromatic Dithiaheptaphyrin(1.0.0.1.1.2.1)s

We report the synthesis of three novel 1,4-pyrene-embedded heptaphyrins in 5% yields via a [5 + 2] condensation of 1,4-pyrene pentapyrrane with dipyrromethene diols under mild acid-catalyzed conditions, followed by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) oxidation. The key precursors, 1,4-pyrene pentapyrrane and 1,4-pyrene diol, were prepared from the literature-known 1,4-dithienylpyrene. While the previous pyreniporphyrinoids predominantly employed 1,3- or 1,3,6,8-linkages, this study represents the first-time use of exclusive 1,4-pyrene linkage to synthesize expanded macrocycles. These macrocycles were thoroughly studied using MALDI-MS, NMR, UV-visible absorption spectroscopy, electrochemical techniques, and theoretical calculations. The pyrene-embedded heptaphyrins are stable and display characteristic nonaromatic absorption features with absorption band at ~371 nm arising from pyrene moiety, while the sharp band at 478 nm and broad band in the 529-806 nm originating from the macrocyclic framework. Upon protonation, this broad band undergoes a significant bathochromic shift into the near-infrared (NIR) region, whereas the other two absorption bands remain unchanged or exhibit only a marginal red shift. Furthermore, electrochemical studies show that the macrocycles are electron-rich, exhibiting two irreversible oxidations and a reversible reduction. Ground-state optimization of the macrocycles reveals highly distorted, non-coplanar geometries with disrupted π-delocalization. Their nonaromatic character is further supported by NICS(0) calculations.