POTENTIAL PHOTOSENSITIZERS FOR PHOTODYNAMIC THERAPY .4. PHOTOPHYSICAL AND PHOTOCHEMICAL PROPERTIES OF AZAPORPHYRIN AND AZACHLORIN DERIVATIVES

The photophysical and photochemical properties of a 5-azaprotoporphyrin derivative ([5]AZPP), a zinc-15-azaporphyrin derivative (Zn-[15]AZIDP) and an E-Z isomeric mixture of a 5-azachlorin derivative ([5]AZCH) were studied in various solvents. The quantum yields of fluorescence PHI(F)0, S1-T1 intersystem crossing PHI(T)0 and singlet oxygen (1DELTA(g) formation PHI(DELTA) were measured and the Stern-Volmer constants for the quenching of the S1 states by oxygen and the rate constants of quenching of O2(1DELTA(g)) by the different azaporphyrinoid compounds were obtained. The fluorescence quantum yield (PHI(F)0 = 0.23), the strong absorption in the red (LAMBDA(max) = 674 nm, epsilon(max) = 66 000 M-1 cm-1) and the high value of the quantum yield for singlet oxygen (1DELTA(g)) formation (PHI(DELTA) = 0.65) observed for [5]AZCH recommend azachlorin derivatives as potential markers and photosensitizers for tumour therapy.