Doubly Fused Unsymmetrical Calixdicarbahexaphyrins

Three novel doubly fused unsymmetrical calixdicarbahexaphyrins were synthesized by mild acid-catalyzed (4+2) condensation of dicarbatetrapyrrane with dipyrroethene diol followed by oxidation. The condensation formed doubly fused calixdicarbahexaphyrins instead of pi-conjugated dicarbahexaphyrins, due to the unusual fusion of the pyrrole N with the alpha-carbon of the adjacent pyrrole ring to form a tripentacyclic ring and one usual fusion of the pyrrole N with the adjacent phenylene C to form a fused moiety containing two pentacycles and one hexacycle ring. Both fusions occurred on one side of the macrocycle, making the macrocycles unsymmetric. The crystal structure obtained for one of the macrocycles exhibited a saddle-shaped structure with two benzene rings and four pyrrole rings connected via two ethylene and four methene meso-carbon atoms. The crystal structure also revealed unusual fusions in the macrocyclic framework and the presence of one sp(3) carbon that disrupts the pi-electron delocalization. H-1,H- 1-H-1 COSY, NOESY, C-13, and HMBC NMR techniques were used to characterize the macrocycles. The absorption spectra of the macrocycles showed one intense sharp band at similar to 485 nm along with a shoulder in the lower-energy region, suggesting its non-aromatic nature. Electrochemical studies indicated their electron rich nature, and DFT/TD-DFT studies corroborated the experimental observations.

Automated summary

A series of novel doubly fused unsymmetrical calixdicarbahexaphyrins were synthesized through acid-catalyzed condensation. The macrocycles exhibited unsymmetrical structure with unusual fusions and disrupted π-electron delocalization. Experimental and theoretical studies confirmed their characteristics and properties.