Fluorescent cyclodextrin carriers for a water soluble ZnII pyrazinoporphyrazine octacation with photosensitizer potential

A nitro-benzofurazan-triazolyl carboxymethylated ?-cyclodextrin (NBFT-CM?CyD) and an oligomer of carboxymethyl ?-cyclodextrin (sodium salt), crosslinked with epichlorohydrin and labeled with rhodaminyl groups (p?CyD-Rh), exhibit very high affinity in aqueous solution for the octacationic photosensitizer [(CH3)8LZn]8+ neutralized by I- ions (L = tetrakis-2,3-[5,6-di(2- (pyridiniumyl)pyrazino]porphyrazinato dianion). [(CH3)8LZn]8+ forms complexes with 1:2 and 2:2 CyD: [(CH3)8LZn]8+ stoichiometry, characterized in terms of binding constants and UV-Vis absorption and fluorescence properties.1 The selfassociation tendency of [(CH3)8LZn]8+, leading to a monomer-dimer equilibrium shifted toward the dimer even at very low concentrations (?10-6 M), is not contrasted by either NBFT-CM?CyD or the p?CyD-Rh oligomer. Indeed both completely convert the [(CH3)8LZn]8+ monomer fraction to the dimer form in the bound state. Quenching of fluorescence observed in [(CH3)8LZn]8+ upon binding with the hosts is consistent with conversion of the monomer to the negligibly fluorescent dimer. The complexes formed with the CM?CyD units of the p?CyD-Rh oligomer have average association constants larger by 6-7 order of magnitudes than those with the CM?CyD monomer in the NBFT-labeled derivative.