OXYGEN QUENCHING OF EXCITED ALIPHATIC-KETONES AND DIKETONES

The oxygen quenching rate constants of aliphatic ketones (acetone, 2-p entanone, 2-hexanone, 4-heptanone) and diketones (biacetyl and camphor quinone) have been determined for the singlet- and triplet-excited sta te by time-resolved fluorescence and triplet transient absorption spec troscopy, and the quantum yields for singlet oxygen formation were mea sured. It was observed that the quenching rate constants for the singl et state of aliphatic ketones are considerably smaller than for their triplet states. The efficiencies for singlet oxygen production of the aliphatic ketones were 0.2-0.3, while those of most diketones fall in the 0.4-0.6 range. The changes in the efficiencies for singlet oxygen production and of the oxygen-quenching rate constants for singlet- and triplet-excited n,pi states, ketones and azoalkanes are discussed in terms of variations in excited state energies and charge-transfer int eractions with oxygen.