Cholate-interspersed porphyrin–anthraquinone conjugates: Photonuclease activity of large sized, ‘tweezer-like’ molecules

Abstract

In a new approach towards the development of a ‘dual-wavelength dual-mechanism’ type of photosensitizer for use in photodynamic therapy (PDT), covalently linked bichromophoric systems comprising of porphyrin (P) and anthraquinone (AnQ) subunits have been synthesized and fully characterized by FAB-MS, IR, UV–Visible and ¹H NMR methods. The porphyrin donor and the anthraquinone acceptor subunits of these mono- or bis-intercalating hybrid molecules are interspersed with either cholate or polymethylene spacers. There exists minimal ground- and singlet-state interaction between the porphyrin and anthraquinone subunits in the giant-sized, cholate-interspersed P–AnQ systems as revealed by a comparison of their spectroscopic and electrochemical properties with those of the corresponding individual reference compounds. On the other hand, quenching of fluorescence observed for the P–AnQ systems endowed with polymethylene spacers has been interpreted in terms of a possible intramolecular electron transfer between the singlet porphyrin and the anthraquinone acceptor. When excited into their porphyrin absorption band maxima, each new P–AnQ system could generate singlet molecular oxygen in good-to-moderate yield. Wavelength-dependent photonuclease activity of these new bis-intercalating species has been examined.