Photoprocesses of molecules with 2-nitrobenzyl protecting groups and caged organic acids.
The 308 nm photoinduced formation of the nitroso product and the intermediacy of the aci-nitro form(s) were studied for a series of 2-nitrobenzyl alkyl and aryl esters (1a-4e) and bis-(nitrophenyl)methyl acetates (5a-6b) by time-resolved UV-vis spectroscopy. A triplet state appears as major transient, when 2-nitrobenzyl derivatives 1 are substituted by 4,5-dimethoxy (2) and 4,5-methylenedioxy (3/4) groups. This triplet of charge transfer character is, however, not part of the route via the aci-nitro into the 2-nitroso form. The activation energy and preexponential factor of the longest lifetime component (tau(aci)), i.e. the major part of the aci-nitro decay, were determined. The carboxylic acids as leaving groups have rather small effects on tau(aci). An additional nitrated phenyl ring in alpha-position (5) leads generally to shorter tau(aci) value. Otherwise, the photogeneration of nitroso products is similar. The quantum yield (Phi(d)) varies only moderately with structure, the yield of the aci-nitro form and Phi(d) are correlated and little affected by solvent properties.
Bley
Filiz
F
Institut für Organische Chemie und Makromolekulare Chemie, Universitätsstr. 1, Düsseldorf, Germany.
Schaper
Klaus
K
Görner
Helmut
H
D000085:Acetates / Q000737:chemistry; D000143:Acids / Q000737:chemistry*; D015394:Molecular Structure; D009578:Nitrobenzenes / Q000737:chemistry*; D009930:Organic Chemicals / Q000737:chemistry*; D010777:Photochemistry; D014050:Toluene / Q000737:chemistry
D000085:Acetates; D000143:Acids; D009578:Nitrobenzenes; D009930:Organic Chemicals; D014050:Toluene