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 D2‐symmetric porphyrin trimer host. Two units of the two‐armed porphyrin and one unit of the four‐armed porphyrin self‐assembled quantitatively into the D2‐symmetric porphyrin trimer, stabilized through ammidinium‐carboxylate salt bridge formation, in CH2Cl2 and CHCl3. 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 K1 (2.1±0.4×105 M−1) and K2 (2.2±0.06×104 M−1) in CHCl3 at room temperature. [ABSTRACT FROM AUTHOR]