Noncovalent Intermolecular Interaction in Cofacially Stacked 24π Antiaromatic Hexaphyrin Dimer

pi-pi Stacking is omnipresent not only in nature but in a wide variety of practical fields applied to our lives. Because of its importance in a performance of natural and artificial systems, such as light harvesting system and working layer in device, many researchers have put intensive effort into identifying its underlying nature. However, for the case of pi-pi stacked systems composed of antiaromatic units, the understanding of the fundamental mechanisms is still unclear. Herein, we synthesized a new type of planar beta,beta'-phenylene-bridged hexaphyrin (1.0.1.0.1.0), referred as naphthorosarin which possesses the 24 pi-electron conjugated pathway. Especially, the corresponding antiaromatic porphyrinoid shows the unique property to form dimeric species adopting the face-to-face geometry which is unprecedented in cases of known annulated naphthorosarins. In order to elucidate the intriguing properties derived from the stacked dimer, the current study focuses on the experimental support to rationalize the observed pi-pi interactions between the two subunits.