A porphyrin molecule that generates, traps, stores, and releases singlet oxygen

Tetraphenylporphyrin (H2TPP), covalently linked to four 2-pyridone moieties was synthesized (II) and studied. This composite molecule, in combination with light and ground state oxygen, has the ability to generate, trap, store, and release singlet oxygen. The process can be operated reversibly without detectable decomposition or side reactions using light with wavelength greater than 500 nm. Oxidation of the target molecule, 2-chloroethyl ethyl sulfide (CEES), by singlet oxygen released from the endoperoxide of the porphyrin-2-pyridone molecule (I) is demonstrated. Spectroscopic and kinetic data do not reveal evidence of perturbation between the porphyrin and pyridone ring systems of II. The decomposition kinetics for the endoperoxide adduct I are first order with activation parameters ΔH‡ = 26.7 (kcal/mol) and ΔG‡ = 24.0 (kcal/mol). Experimental and computational studies of unattached N-benzyl-2-pyridone peroxide are reported and compared to the experimental data for I.