Fig. 4.

Singlet oxygen generation and quenching. (A and B) Phosphorescence of singlet oxygen generated from A2E, atRALdi-E, and atRALdi. (A) A2E, atRALdi, and atRALdi-E (50 μM in CCl₄) were irradiated at 430 nm, and the generation of singlet oxygen was detected by its phosphorescence in the near infrared region. atRAL di-E was irradiated in the presence of TFA (atRALdi-E + TFA) or the absence of TFA (atRALdi-E) to test for the effect of protonation of the Schiff base nitrogen on the singlet oxygen yield. (B) Effect of protonation of atRALdi-E and illumination wavelength on the generation of singlet oxygen. atRALdi-E was excited at either 430 nm or 500 nm in the presence or absence of TFA. (C and D) Comparison of tendency of A2E and atRAL dimer-E (atRALdi-E) to quench singlet oxygen. A2E (C) and atRALdi-E (D) were oxidized by singlet oxygen generated from the endoperoxide of 1,4-dimethylnaphthalene. FAB-MS spectra are shown. A2E and atRALdi-E are detected as molecular ion peaks at m/z ratios of 592 and 594, respectively.