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

In a new approach towards the development of a 'dual-wavelength dual-mechan ism' type of photosensitizer for use in photodynamic therapy (PDT), covalen tly linked bichromophoric systems comprising of porphyrin (P) and anthraqui none (AnQ) subunits have been synthesized and fully characterized by FAB-MS , IR, UV-Visible and H-1 NMR methods. The porphyrin donor and the anthraqui none acceptor subunits of these mono- or bis-intercalating hybrid molecules are interspersed with either cholate or polymethylene spacers. There exist s minimal ground- and singlet-state interaction between the porphyrin and a nthraquinone subunits in the giant-sized, cholate-interspersed P-AnQ system s as revealed by a comparison of their spectroscopic and electrochemical pr operties with those of the corresponding individual reference compounds. On the other hand, quenching of fluorescence observed for the P-AnQ systems e ndowed with polymethylene spacers has been interpreted in terms of a possib le intramolecular electron transfer between the singlet porphyrin and the a nthraquinone acceptor. When excited into their porphyrin absorption band ma xima, each new P-AnQ system could generate singlet molecular oxygen in good -to-moderate yield. Wavelength-dependent photonuclease activity of these ne w bis-intercalating species has been examined.