Cai Xichen, Sakamoto Masanori, Hara Michihiro, Tojo Sachiko, Ouchi Akihiko, Sugimoto Akira, Kawai Kiyohiko, Endo Masayuki, Fujitsuka Mamoru, Majima Tetsuro
National Institute of Advanced Industrial Science and Technology, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8565, Japan.
J Phys Chem A. 2005 May 5;109(17):3797-802. doi: 10.1021/jp050232q.
Stepwise photocleavage of naphthylmethyl-oxygen (C-O) bonds of mono(substituted-methyl)naphthalenes [1- and 2-ROCH2Np, R = 4-benzoylphenyl (BP), phenyl (Ph), and methyl (CH3)] and bis(substituted-methyl)naphthalenes [1,8-(ROCH2)2Np and 1,4-(ROCH2)2Np, R = BP and Ph] was observed to give the naphthylmethyl radicals (NpCH2* or ROCH2NpCH2*) in almost 100% yield with two-step or three-step excitation by the two-color two-laser or three-color three-laser irradiation, respectively, at room temperature. The C-O bond cleavage quantum yields of 1-PhOCH2Np, 2-PhOCH2Np, 1,8-(PhOCH2)2Np, and 1,4-(PhOCH2)2Np were higher than those of 1-BPOCH2Np, 2-BPOCH2Np, 1,8-(BPOCH2)2Np, and 1,4-(BPOCH2)2Np. No C-O bond cleavage occurred from 1,8-(HOCH2)2Np and 2-CH3OCH2Np in the higher triplet excited state (T(n)). The experimental results show that the C-O bond cleavage was determined not only by the position of the substituents on Np but also by the type of the substituents. The C-O bond cleavage of 1-ROCH2Np was more efficient than that of 2-ROCH2Np. In the case of 1,8-(ROCH2)2Np and 1,4-(ROCH2)2Np (R = BP and Ph), the first C-O bond cleavage from the T(n) states occurred to give ROCH2-substituted naphthylmethyl radicals (1,8- and 1,4-ROCH2NpCH2*) when the T1 states, generated with the 308-nm first laser irradiation, were excited using the 430-nm second laser. The second C-O bond cleavage occurred when 1,8- and 1,4-ROCH2NpCH2* in the ground state [1,8- and 1,4-ROCH2NpCH2*(D0)] were excited to the excited states [1,8- and 1,4-ROCH2NpCH2*(D(n))] using the third 355-nm laser during the three-color three-laser flash photolysis at room temperature. It was revealed that acenaphthene was produced as the final product during the stepwise C-O bond cleavages of 1,8-(BPOCH2)2Np and 1,8-(PhOCH2)2Np. This is a successful example of stepwise cleavage of two equivalent C-O bonds in a molecule using the three-color three-laser photolysis method.
在室温下，通过双色双激光或三色三激光照射分别进行两步或三步激发，观察到单（取代甲基）萘[1-和2-ROCH₂Np，R = 4-苯甲酰基苯基（BP）、苯基（Ph）和甲基（CH₃）]以及双（取代甲基）萘[1,8-(ROCH₂)₂Np和1,4-(ROCH₂)₂Np，R = BP和Ph]的萘基甲基-氧（C-O）键逐步光裂解，几乎以100%的产率生成萘基甲基自由基（NpCH₂或ROCH₂NpCH₂）。1-PhOCH₂Np、2-PhOCH₂Np、1,8-(PhOCH₂)₂Np和1,4-(PhOCH₂)₂Np的C-O键裂解量子产率高于1-BPOCH₂Np、2-BPOCH₂Np、1,8-(BPOCH₂)₂Np和1,4-(BPOCH₂)₂Np。在较高的三重激发态（T(n)）下，1,8-(HOCH₂)₂Np和2-CH₃OCH₂Np未发生C-O键裂解。实验结果表明，C-O键裂解不仅取决于萘上取代基的位置，还取决于取代基的类型。1-ROCH₂Np的C-O键裂解比2-ROCH₂Np更有效。对于1,8-(ROCH₂)₂Np和1,4-(ROCH₂)₂Np（R = BP和Ph），当用308 nm的第一激光照射产生T1态后，用430 nm的第二激光激发时，从T(n)态发生第一次C-O键裂解，生成ROCH₂取代的萘基甲基自由基（1,8-和1,4-ROCH₂NpCH₂*）。在室温下进行三色三激光闪光光解时，当基态的1,8-和1,4-ROCH₂NpCH₂*[1,8-和1,4-ROCH₂NpCH₂*(D0)]用第三束355 nm激光激发到激发态[1,8-和1,4-ROCH₂NpCH₂*(D(n))]时，发生第二次C-O键裂解。结果表明，在1,8-(BPOCH₂)₂Np和1,8-(PhOCH₂)₂Np的C-O键逐步裂解过程中，苊作为最终产物生成。这是使用三色三激光光解方法在分子中逐步裂解两个等效C-O键的成功实例。
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