Quenching of Singlet Oxygen by 1,3,5-Triaryl-2-pyrazolines

Article abstract of DOI:10.1021/jo00152a025

The efficient quenching of photochemically generated singlet oxygen by four 1,3,5-triaryl-2-pyrazolines (5-8) and p-(diethylamino)benzaldehyde diphenylhydrazone (9) has been investigated by inhibition of the photosensitized oxygenation of 1,3 diphenylisobenzofuran and 2-methyl-2-pentene. 1-Phenyl-3--5--2-pyrazoline (8) quenches singlet oxygen without any reaction at all, and the quenching rate constant reaches a maximum of 5.8 x 10⁹ M^-1 s^-1.The quenching ability correlates with the value of their one-electron oxidation potentials (E_p).