THE EFFECT OF SOLVENT DEUTERATION ON THE PHOTOPHYSICS OF SULFONATED ALUMINUM PHTHALOCYANINE

The photophysics of disulphonated aluminium phthalocyanine in protiated and deuterated aqueous phosphate-buffered saline solution are reported. In the deuterated solvent the rate coefficients of fluorescence and intersystem crossing are unaffected by the heavier isotope; however, the rate of internal conversion from S1 to S0 has been shown to be considerably reduced. This results in increased quantum yields of fluorescence and triplet-state formation and also increased triplet and singlet lifetimes in deuterium oxide (PHI(f)=0.40+/-0.04, tau(f)=5.1+/-0.1 ns and tau(t)=600+/-30 mus in H2O and PHI(f)=0.52+/-0.06, tau(f)=6.8+/-0.1 ns and tau(t)=1590+/-100 mus in D2O). The implications of this with respect to the determination of the quantum yields of singlet oxygen formation in D2O are discussed.