A Five‐layer π‐Aromatic Structure Formed through Self‐assembly of a Porphyrin Trimer and Two Aromatic Guests

In this study we synthesized two‐ and four‐armed porphyrins – bearing two carboxyl and four 2‐aminoquinolino functionalities, respectively, at their meso positions – as a complementary hydrogen bonding pair for the self‐assembly of a D 2 ‐symmetric porphyrin trimer host. Two units of the two‐armed porphyrin and one unit of the four‐armed porphyrin self‐assembled quantitatively into the D 2 ‐symmetric porphyrin trimer, stabilized through ammidinium‐carboxylate salt bridge formation, in CH 2 Cl 2 and CHCl 3 . The porphyrin trimer host gradually bound two units of 1,3,5‐trinitrobenzene between the pair of porphyrin units, forming a five‐layer aromatic structure. At temperatures below −40 °C, the rates of association and dissociation of the complexes were slow on the NMR spectroscopic time scale, allowing the 1 : 1 and 1 : 2 complexes of the trimer host and trinitrobenzene guest(s) to be detected independently when using less than 2 eq of trinitrobenzene. Vis titration experiments revealed the values of K 1 (2.1±0.4×10 5  M −1 ) and K 2 (2.2±0.06×10 4  M −1 ) in CHCl 3 at room temperature.