Concerning the Absorption and Photochemical Properties of an ω-4-Dimethylaminobenzal Hypericin Derivative

Summary.

 A hypericin derivative containing ω,ω ′-4-dimethylaminobenzal residues was shown to undergo an intramolecular [2 + 2] cycloaddition upon irradiation leading to a cyclobutane derivative whose main absorption band is hardly shifted as compared to hypericin. The corresponding ω-substituted derivative displayed a 34 nm bathochromic shift and a strongly reduced fluorescence quantum yield rendering it a nice candidate for a photodynamic therapy agent. Unfortunately, however, it produced virtually no photosensitized active oxygen species, making it thus unsuited for this purpose.