Wavelength-Dependent Efficiency of Sequential Photooxygenation: C=C Bond Cleavage on Open-Cage C Derivatives.

We have studied the efficiency of the C=C double bond cleavage on open-cage fullerene C derivatives by singlet oxygen using four different LED lamps including UV, blue, green, and red radiation. The results indicate that red radiation is the most efficient for this photochemical oxidation owing to the sufficient penetration of the longer-wavelength light. By applying this method to a 2-methoxyethoxymethyl-substituted azafulleroid derivative, we demonstrated the sequential double photooxygenation which provides a symmetric diketo imide derivative having a 15-membered-ring opening via stepwise cleavage of two C=C double bonds. Using a H -encapsulating derivative, we further examined the size of the opening by comparison with the structural isomer, based on H -release experiments and theoretical calculations.