405-nm LED light (8332C, CCS Inc.) was collimated by a convex lens (f = 25 mm) and the light was irradiated to the solution in a 10-mm quartz cuvette (Supplementary Fig. ). The spot area and the intensity were set to 1 cm 2 and 100-850 mW, respectively. The irradiation period was controlled by a homemade code using MATLAB.