PHOTOPHYSICAL AND PHOTOSENSITIZING PROPERTIES OF 2‐AMINO‐4 PTERIDINONE: A NATURAL PIGMENT

Abstract

Abstract— The characteristics of the fluorescence and phosphorescence emission of 2‐amino‐4 (3H) pteridinone (or pterin) in aqueous solutions are pH dependent. The room temperature fluorescence quantum yield is low and is maximum at pH = 10 (φ F ∼ 0.057). The 77K phosphorescence emission consists of two overlapping emissions originating from τ* triplet states. In agreement with low temperature results, the 353nm laser flash photolysis makes it possible to detect at pH 9.2, two transient triplet absorptions (τ 1 ∼ 0.3 μs and τ 2 ∼ 2.3 μs). The longer lived triplet is characterized by φ TM ∼ 0.20 and ∼ (550nm) = 2000 M −1 cm −1 . It reacts with the solvent forming the semireduced pterin with a quantum yield φ R ∼ 0.06. The photosensitizing properties of pterin have been studied by laser flash spectroscopy and steady state irradiations. Photoreactions implying singlet oxygen formation are shown to occur. Laser flash spectroscopy indicates that the pterin triplet is reduced by amino acids and nucleic acid bases. Corresponding bimolecular reaction rate constants have been measured.