Strapped porphyrin rosettes based on the melamine-cyanuric acid motif. Self-assembly and supramolecular recognition

This paper describes studies on the synthesis, self-assembly behavior, and complexing properties of several strapped porphyrin-incorporated melamine-cyanuric or melamine-barbiturate-based rosette supramolecules in chloroform-d. Strapped porpyrin cyanuric acid H₂1 and its Zn (II) complex Zn1 were designed and synthesized. Both H₂1 and Zn1 could combine melamine derivatives 11 or 12 to afford porphyrin rosettes, which are more stable than the model rosette initially reported by Whitesides due to the larger size of the porphyrin unit. The new porphyrin rosettes could efficiently complex tripyridyl derivative 13 through intermolecular, cooperative coordination between Zn (II) and pyridine. Two new pyridine-bearing barbiturates 18a and 18b were also synthesized. Mixing the identical amount of 18a or 18b with 11 or 12 in chloroform-d led to the formation of new isomeric rosettes as a result of different orientation of the pyridine unit of 18a or 18b in the rosettes. ¹H NMR study also revealed that porpyrin-bearing rosette Zn1₃·11₃ could complex pyridine-bearing rosette 11₃·18a₃, leading to the formation of new two-layer-typed supramolecular architectures.