ABSTRACT 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.
Varak et al. (Thu,) studied this question.