D. Murtinho et al., Novel porphyrins and a chlorin as efficient singlet oxygen photosensitizers for photooxidation of naphthols or phenols to quinones, J CHEM S P2, (12), 2000, pp. 2441-2447
Citations number
46
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2
Four porphyrins and one chlorin having aromatic groups at the meso position
have been synthesized and tested as potential sensitizers for the photooxi
dation of phenols. The yields of conversion of 1,5-dihydroxynaphthalene and
2,3,5-trimethylphenol to their corresponding quinones have been determined
following photolysis in air-saturated acetonitrile-dichloromethane solutio
ns in the presence of these compounds, and are higher than those obtained u
sing other photosensitizers. The reactions are shown to proceed via formati
on of singlet oxygen ((1)Delta (g)), followed by its addition to the phenol
. A mechanism is presented. Rates of reaction of singlet oxygen with the su
bstrates were determined by studying the decay of the O-1(2)* emission. Sin
glet oxygen quantum yields and formation efficiencies for the photosensitiz
ers have been determined by laser flash photolysis and photoacoustic calori
metry. In addition, for two of the porphyrins, these were also measured usi
ng time-resolved luminescence. In all cases, highly efficient singlet oxyge
n formation is observed. The stabilities of the sensitizers to prolonged ph
otolysis were studied. The compound 5,10,15,20-tetrakis(2,6-dichlorophenyl)
porphyrin was found to be a particularly efficient photosensitizer for oxid
ation of phenols. It is suggested that this is due both to its high singlet
oxygen yield and to its good photostability.