Bley Filiz, Schaper Klaus, Görner Helmut
Institut für Organische Chemie und Makromolekulare Chemie, Universitätsstr. 1, Düsseldorf, Germany.
Photochem Photobiol. 2008 Jan-Feb;84(1):162-71. doi: 10.1111/j.1751-1097.2007.00215.x.
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.
通过时间分辨紫外可见光谱，研究了一系列2-硝基苄基烷基酯和芳基酯（1a - 4e）以及双（硝基苯基）甲基乙酸酯（5a - 6b）在308 nm光诱导下亚硝基产物的形成以及酸式硝基形式中间体的情况。当2-硝基苄基衍生物1被4,5-二甲氧基（2）和4,5-亚甲基二氧基（3/4）基团取代时，三重态作为主要瞬态出现。然而，这种具有电荷转移特性的三重态并非经由酸式硝基转化为2-亚硝基形式途径的一部分。测定了最长寿命组分（tau(aci)）的活化能和指前因子，即酸式硝基衰变的主要部分。作为离去基团的羧酸对tau(aci)的影响相当小。α位的另一个硝化苯环（5）通常会导致tau(aci)值更短。否则，亚硝基产物的光生成情况相似。量子产率（Phi(d)）仅随结构有适度变化，酸式硝基形式的产率与Phi(d)相关，且受溶剂性质影响较小。
