A Five-layer pi-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 aD(2)-symmetric porphyrin trimer host. Two units of the two-armed porphyrin and one unit of the four-armed porphyrin self-assembled quantitatively into theD(2)-symmetric porphyrin trimer, stabilized through ammidinium-carboxylate salt bridge formation, in CH(2)Cl(2)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 degrees 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 ofK(1)(2.1 +/- 0.4x10(5) M-1) andK(2)(2.2 +/- 0.06x10(4) M-1) in CHCl(3)at room temperature.