Meso-Engineered Carbaporphyrin Dimers with Nonaromatic and Antiaromatic Properties

Carbaporphyrinoids that include polycyclic aromatic hydrocarbons (PAHs) have been drawing increasing attention in recent years. An extensive variety of PAH moieties have been introduced into the carbaporphyrinoid backbone to modulate the electronic structure and aromaticity, although meso-position-based modulation remains underdeveloped. In this work, a meso-oxo substituted dibenzo[g,p]chrysene (DBC)-bridged carbaporphyrin dimer 2 was synthesized and characterized. The compound is nonaromatic with an efficient intersystem crossing (ISC), which can be attributed to strong spin-orbit coupling (SOC) between the nonbonding and π-orbitals in the aromatic ketone subunit. The reaction of the dimer with malononitrile in pyridine affords a meso-tricyanovinyl substituted DBC-bridged carbaporphyrin 3. Contrary to the dimer, compound 3 features pronounced antiaromatic characteristics, as corroborated by combined spectroscopic and density functional theory (DFT) studies. These findings underscore that meso-functionalization offers a strategic pathway toward the design of carbaporphyrinoid frameworks with tailored electronic behavior.