EXCITATION OF VIOLANTHRONE BY SINGLET OXYGEN . A CHEMILUMINESCENCE MECHANISM

When a solution of violanthrone is exposed to a stream of singlet oxygen in a discharge flow system, a red luminescence is emitted from the solution. The glow is found to be independent of the O2(1Σg+) concentration. From the apparent second-order dependence of the glow on the O2(1Δg) concentration and the strong quenching effect of O2(3Σg-), it is concluded that the excitation does not occur in a termolecular collision. An alternative mechanism which involves the excitation of a postulated low-lying triplet state of violanthrone followed by an energy disproportionation between the triplet and O2(1Δg) is consistent with all the experimental results. In view of these observations, the bright chemiluminescence from the reaction mixture H2O-Cl2-violanthrone can be attributed to energy transfer from O2(1Δg) which is known to be present in the reaction mixture.