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Photoprocesses of Molecules with 2‐Nitrobenzyl Protecting Groups and Caged Organic Acids
Author(s) -
Bley Filiz,
Schaper Klaus,
Görner Helmut
Publication year - 2007
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2007.00215.x
Subject(s) - chemistry , quantum yield , nitroso , nitro , alkyl , yield (engineering) , solvent , aryl , photochemistry , medicinal chemistry , molecule , methylenedioxy , ring (chemistry) , organic chemistry , materials science , fluorescence , physics , halogen , quantum mechanics , metallurgy
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 (τ aci ), i.e. the major part of the aci ‐nitro decay, were determined. The carboxylic acids as leaving groups have rather small effects on τ aci . An additional nitrated phenyl ring in α‐position ( 5 ) leads generally to shorter τ aci value. Otherwise, the photogeneration of nitroso products is similar. The quantum yield ( Φ d ) varies only moderately with structure, the yield of the aci ‐nitro form and Φ d are correlated and little affected by solvent properties.