On the syntheses and photochemical properties of heterocyclic ketones as photosensitizers

Article abstract of DOI:10.1016/0584-8539(94)80115-0

The syntheses, and the electrochemical and photochemical properties of the fluorenone analogues 9H-pyrrolo<1,2-a>indole-9-one (1), and 9H-pyrido<3,4,b> pyrrolizin-9-one (2), which absorb in the visible region (ε^400nm=4711 mol^-1 cm^-1 for 1 and ε^400nm=8721 mol^-1 cm^-1 for 2), are described. 9-Fluorenone as well as compounds 1 and 2 were able to reduce methyl viologen in the presence of 2-propanol under irradiation with UV light (λ>280 nm).Compounds 1 and 2 showed an interesting absorption and fluorescence behavior depending on concetration, solvent and pH value.Aqueous solutions of compound 1 gave two fluorescence maxima at 395 and 478 nm, when excited by λ^EX=302 and 368 nm, respectively.In contrast, aqueous solutions of compound 2 showed only one emission maximum at 417 nm (excited by λ^EX=296 or 378 nm).Fluorescence quantum yields (solvent: propanol, excitation wavelength λ^EX=436 nm) for compounds 1 and 2 were 0.2percent.Compounds 1 and 2 showed irreversible reduction potentials at -850 and -560 mV (vs NHE), respectively.The results were compared with benzophenone and 9-fluorenone.