QUANTUM YIELDS OF TRIPLET AND O2(1∆g) FORMATION OF 4‐THIOURIDINE IN WATER AND ACETONITRILE

The quantum yield of triplet formation, ΦT, and that of the photosensitized formation of singlet molecular oxygen, Φ∆, were determined for a rare nucleoside, 4‐thiouridine (4t‐Urd), in water and in acetonitrile, using singlet molecular oxygen phosphorescence, laser‐induced optoacoustics and time‐resolved thermal lensing. These yields, ΦT and Φ∆, the latter in aerated solutions, were found to be, respectively, in water: 0.67 ± 0.17 and 0.18 ± 0.04 and in acetonitrile: 0.61 ± 0.15 and 0.50 ± 0.20. The fraction of the 4t‐Urd triplet molecules quenched by oxygen leading to singlet molecular oxygen, S∆, was calculated to be between 0.7 and unity in both solvents, this value being indicative of a ππ* character for the lowest triplet state of 4t‐Urd.