Photodiemisfry and zyxwvutsrqponm Photobiology. zyxwvutsrqpo Val. zyxwvutsrqp 58, zyxwvutsrqponml No. zyxwvutsrq 1, pp. 3 1-36, I993 Printed in the United States. All rights reserved 003 1-8655/93 $05.00+0.00 z 8 1993 American Society for Photobiology ABSORPTION AND FLUORESCENCE SPECTROSCOPIC STUDIES ON DIMERIZATION OF CHLOROALUMINUM (111) PHTHALOCYANINE TETRASULFONATE IN AQUEOUS ALCOHOLIC SOLUTIONS MINJOONG YOON*’, YOUNCJIN CHEON’ and DONGHO KIM2 lDepartment of Chemistry, Chungnam National University, Taejon zyxw 305-764, Korea and ’Spectroscopy Laboratory, Korea Research Institute of Standards and Science, Taejon 305-606, Korea (Received 23 July 1992; accepted 4 January 1993) Abstract-Dimerization of chloroaluminum (111) phthalocyanine tetrasulfonates (AIPCS) has been observed in dif- ferent aqueous alcoholic solvents at room temperature by absorption and fluorescence spectroscopic methods. Both absorption and fluorescence spectral bands of the dimer are red shifted by zyxwv cu 550 cm-’ from the monomer Q bands in the corresponding spectra, suggesting that the interaction energy between the two monomer subunits is very weak. The fluorescence lifetime of the dimer is longer (cu 9.5 ns) than that of the monomer (cu 7-8 ns). These spectral behaviors of AlPCS dimer contrast with those of transition-metallaloid phthalocyanine dimers, which usually have a nonfluorescent face-to-face stacking conformation. The dimer fluorescence is interpreted to be due to the fact that the lowest excited singlet state of the dimer is lower in energy than a charge-resonance state, based on the exciton- coupling theory applied to the face-to-face slipping conformation. The dimerization constant determined spectro- metrically decreases with an increase of water content in the aqueous alcoholic solution. Propanol and ethanol have been observed to be more effective than methanol in promoting dimerization. These results indicate that a specific interaction of water with AIPCS plays an important role in the inhibition of dimerization of AIPCS. INTRODUCTION Somc water-soluble metallophthalocyanine sulfonatcs (me- tallo-I’C’S)? have been attracting many investigators’ atten- tions as promising candidates for replacing hematoporphy- rins in photodynamic therapy (PDT) oftumors’.’ due to their stronger absorption in the 680-700 nm region, thc spectral region of high penetration in the skin;’ and their photochem- ical stability. Thc efficient photosensitized killing of malig- nant cclls by phthalocyanine sulfonatcs (PCS)4 has been re- ported to be accomplished by the singlet oxygen (‘0,) generation, and the elficiency of photosensitization has been suggested to be rclatively correlated with the ‘02 quantum yields of the PCS compounds. The photosensitization elfi- ciency ol‘metallo-PCS depends on the central metal, and the compounds containing Al or Zn are the most active? These two compounds have the highest ‘0, quantum yields. Nev- crthclcss somc conflicting arguments on thc photosensitiza- tion mechanism5 arc still not completely ruled out. Most PCS compounds arc soluble in water and very sus- ceptible to formation of dimers or aggregates, but AIPCS (Fig. zyxwvutsrqpo 1) remains monomeric in watcr. It is known that dimcrs are much more inactive than monomers as sensitizers.’ This is one of the reported reasons why AIPCS is a more eficient sensitilcr than ZnPCS for photokilling of mammalian cells6 even though the ‘02 quantum yield ofZnPCS is larger (0.45) *To whom correspondence should be addressed. tAhOrcrrurions: AIPCS, chloroaluminum (111) phthalocyanine tetra- sulfonate; HO, highest occupied; LU, lowest unoccupied; MCA, multichannel analyzer: metallo-PCS, metallophthalocyanine sul- fonatc; MO, molecular orbital; OEP, 2,3,7,8,12,13, I7,l S-octaeth- ylporphin; PDT, photodynamic therapy; TCSPC, time-correlated single photon counting; TPP, 5,10,15,20-tetraphenylporphin; ZnPC‘S, Yinc phthalocyanine tctrasulfonate. than that of AlPCS (0.32).4 Thus, in contrast to the convcn- tional concept, there appears to be no direct quantitative correlation bctween ‘0, formation and cell killing. Possible diffcrcnces between ZnPCS and AIPCS in their intracellular structures and photophysical properties may affect their photosensitization efficiencies. Indecd, for ZnPCS- or Al- PCS-sensitized photohemolysis of human red blood cclls, the endogenous sensitizer has been demonstrated to be more predominantly rcsponsible rather than the extraccllular one.6 Because the intracellular microcnvironment should be dif- ferent from the extraccllular one, incorporation of thc sen- sitizers in biological cells must lcad to modification, which presumably involves thc structural change, disaggregation or aggrcgation. The aggregation of phthalocyanines is normally morc pro- nounced in water than in organic However, AIPCS in water remains monomeric in contrast to ZnPCS, implying that the medium effect on aggregation property of AlPCS may be diffcrcnt from that of other metallo-PCS. This means that the medium effect on aggregation of phthalocyanines cannot bc applied to all the metallo-PCS, and the intracellular structural change of AIPCS may bc different from the cor- responding change of other metallo-PCS. Thus, in order to cxplore this possibility, we havc attempted to investigate concentration dependencies of absorption spectroscopic properties of AlPCS in water and diffcrent aqueous alcoholic solutions. The results indicate that dimerization of AlPCS takes place in aqueous alcoholic solution but not in water. The dimerization constant decreases steadily with the water content. The dirner fluorescence was also observed in parallel with the dimer absorption, which is red shifted form the monomer absorption maximum. These obscrvations are quite opposite to those on the dimcrization properties of the other metallo-PCS. To our knowledge, this report is the first ob- servation of the dimer fluorescencc of AIPCS. 31