The synthesis and photophysical properties of polyether substituted phthalocyanines of potential use in photodynamic therapy

Abstract

The synthesis, photophysical properties and singlet oxygen yields of a range of polyether substituted metallo and free-base phthalocyanines are reported and discussed in the context of the potential use of these compounds as alternatives to haematoporphyrin derivatives (HpD) in the photodynamic therapy (PDT) of cancer. The triplet states of the phthalocyanines have been studied in benzene and methanol using nanosecond laser flash photolysis and pulse radiolysis. Triplet state absorption maxima occur at ca. 510 to 525 nm and the quantum yields of triplet formation (ϕ_T) lie in the range 0.14 to 0.32. Triplet state lifetimes are in the range 26 to 155 µs. Energy transfer from the triplet state (T₁) of the phthalocyanines to ground state molecular oxygen O₂³Σ_g^- to produce singlet oxygen O₂¹ω_g is efficient and evidence is presented for the establishment of an equilibrium in perdeuterated benzene, eqn. (a).Singlet oxygen quantum yields (ϕ_Δ), determined by time resolved near infrared luminescence, are comparable with the triplet yield suggesting a high proportion of quenching encounters result in the formation of singlet oxygen.The photophysical properties of the metallophthalocyanines are dependent on the relative atomic mass and the magnetic properties of the central metal ion.