SYNTHESIS OF BENZOCHLORIN MONOMER, DIMER, AND PORPHYRIN-BENZOCHLORIN HETERODIMER FROM 5-ARYL-OCTAETHYLPORPHYRINS AND 5,15-DIARYL-OCTAETHYLPORPHYRINS

Vinylogous Vilsmeier formylation of nickel(II) 5,15-di-p-tolyl-octaethylporphyrin gave the corresponding meso-(2-formylvinyl)porphyrin, which, on treatment with trifluoroacetic acid, provided the corresponding benzochlorin derivative. In the case of the copper(II) complex, Lewis acid such as BF3 . Et2O and SnCl4 catalyzed the cyclization to the benzochlorin without demetallation. Similar vinylogous Vilsmeier formylation of the nickel(II) and copper(II) complexes of 5-p-tolyloctaethylporphyrin resulted in the selective formation of 5-p-tolyl-10-(2-formylvinyl)porphyrin. Subsequent cyclization of these metal complexes took place with marked different regioselectivity; the nickel(II) complex favors the cyclization at near the 5-p-tolyl substituent, while the copper(II) complex favors the cyclization at the opposite site. Application of these synthetic methods to the 4,4'-biphenylylene-bridged diporphyrin led to the synthesis of porphyrin-benzochlorin heterodimer and benzochlorin homodimer. The steady-state fluorescence spectrum of free base form of the heterodimer suggested the intramolecular singlet excitation energy transfer from the porphyrin to the benzochlorin.