Competitive occurrence of homolytic N-O and heterolytic C-O bond cleavage in excited-state 1-(arylmethyloxy)-2-pyridones
The irradiation at 340 nm of the title compounds having 9-anthryl and pyren-1-yl groups in methanol was found to give the heterolytic C-O bond cleavage products: 1-hydroxy-2-pyridone and aryl-substituted dimethyl ether (which predominate for the reaction of the former title compound) in addition to 2-pyridone, aryl-substituted methanol and aryl-substituted formaldehyde derived from the homolysis of the N-O bond (which mainly occurs in the photolysis of the latter title compound). It was also found that substitution of the methyl group for hydrogen at the 6-position of the pyridone skeleton in 1-(9-anthrylmethyloxy)-2-pyridone decreases the relative composition of the arylsubstituted dimethyl ether to some extent. These substituent effects on the product compositions were explained in terms of stereoelectronic effects on a charge transfer-type interaction between the aromatic and pyridone rings in the singlet excited state. Analyses of the ground-state conformation for the title compounds by MM2 calculations and 1H NMR spectroscopy, as well as of their singlet excited-state behaviour, substantiated the existence of a non-emissive intramolecular exciplex intermediate which plays a key role in inducing the C-O bond heterolysis.
Photoinduced heterolysis of the carbon-oxygen bond in bichromophoric 1- arylmethyloxy-2-pyridones
Irradiation of the title compound having a 9-anthryl (1a) or a 1- pyrenyl group (1b) in methanol was found to give the heterolytic C-O bond cleavage products: 1-hydroxy-2-pyridone and arylmethyl methyl ether, (which predominate for the reaction of 1a), along with 2-pyridone, aryl-substituted methanol and aryl aldehyde derived from the homolysis of the N-O bond (that mainly occurs in the photolysis of 1b). Spectroscopic analysis of the ground- state and excited singlet-state behavior of 1 revealed that a non-emissive intramolecular exciplex (whose formation rate is much faster in 1a than in 1b) plays a key role in inducing the C-O bond heterolysis.
New Photochemically Labile Protecting Group for Phosphates
New photochemically labile phosphate protecting group was developed.These phosphate esters have high molar extinction coefficient (ε340=34500 dm3 mol-1cm-1) and rapidly release parent phosphates upon irradiation (>300 nm) with high quantum efficiency for disappearance (φdis=0.22 at 340 nm).
Photoreactivity of 1-Pyrenylmethyl Esters. Dependence on the Structure of the Carboxylic Acid Moieties and the Nature of the Excited States
While the photolysis of 1-pyrenylmethyl phenylacetates in methanol gave the original phenylacetic acids, irradation of the 1-naphthoate and 9-anthracenecarboxylate leads to the formation of the intramolecular exciplexes that are inert to the photolysis.The Φf and τf values of these esters have been determined.
1-PYRENYLMETHYL ESTERS, PHOTOLABILE PROTECTING GROUPS FOR CARBOXYLIC ACIDS
1-Diazomethylpyrenes were prepared and reacted with carboxylic acids to give 1-pyrenylmethyl esters.The fluorescent esters were photolysed at 340 nm in methanol to form the starting acids and the corresponding 1-methoxymethylpyrenes in high yields.