| Abstract
| - 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 naphthylmethylradicals (NpCH2• or ROCH2NpCH2•) in almost 100% yield with two-step or three-step excitation by thetwo-color two-laser or three-color three-laser irradiation, respectively, at room temperature. The C−O bondcleavage quantum yields of 1-PhOCH2Np, 2-PhOCH2Np, 1,8-(PhOCH2)2Np, and 1,4-(PhOCH2)2Np were higherthan those of 1-BPOCH2Np, 2-BPOCH2Np, 1,8-(BPOCH2)2Np, and 1,4-(BPOCH2)2Np. No C−O bond cleavageoccurred from 1,8-(HOCH2)2Np and 2-CH3OCH2Np in the higher triplet excited state (Tn). The experimentalresults show that the C−O bond cleavage was determined not only by the position of the substituents on Npbut also by the type of the substituents. The C−O bond cleavage of 1-ROCH2Np was more efficient than thatof 2-ROCH2Np. In the case of 1,8-(ROCH2)2Np and 1,4-(ROCH2)2Np (R = BP and Ph), the first C−O bondcleavage from the Tn 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-nmsecond laser. The second C−O bond cleavage occurred when 1,8- and 1,4-ROCH2NpCH2• in the groundstate [1,8- and 1,4-ROCH2NpCH2•(D0)] were excited to the excited states [1,8- and 1,4-ROCH2NpCH2•(Dn)]using the third 355-nm laser during the three-color three-laser flash photolysis at room temperature. It wasrevealed that acenaphthene was produced as the final product during the stepwise C−O bond cleavages of1,8-(BPOCH2)2Np and 1,8-(PhOCH2)2Np. This is a successful example of stepwise cleavage of two equivalentC−O bonds in a molecule using the three-color three-laser photolysis method.
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