Phosphorescence dione

In the Leonard series of four- to eight-membered tetramethyl-cycloalkane diones mentioned earlier in connection with the angular dependence of the four-membered compound gave no-emission, five- and six-membered showed only fluorescence, and the two larger ring members exhibited both fluorescence and phosphorescence 9). The separation between absorption and fluorescence varied as expected from the assumption of planar emitting and non-planar absorbing species. 

Radical 80 has been prepared as its perchlorate salt by anodic oxidation in ethyl acetate in the presence of hthium perchlorate. The reactivity toward nucleophiles of material so prepared was investigated nitrite and nitrate ions give 2-nitrodibenzo[l,4]dioxin although the mechanisms of the reactions are not clear. Pyridine gives 7V-(2-dibenzo[l,4]dioxinyl)pyridinium ion (84). Other nucleophiles acted as electron donors and largely reduced 80 back to the parent heterocycle they included amines, cyanide ion and water. In an earlier study, the reaction of 80 with water had been examined and the ultimate formation of catechol via dibenzo[l,4]dioxin-2,3-dione was inferred. The cation-radical (80) has been found to accelerate the anisylation of thianthrene cation-radical (Section lII,C,4,b) it has been found to participate in an electrochemiluminescence system with benzo-phenone involving phosphorescence of the latter in a fluid system, and it has been used in a study of relative diffusion coefficients of aromatic cations which shows that it is justified to equate voltammetric potentials for these species with formal thermodynamic redox potentials. The dibenzo[l,4]dioxin semiquinone 85 has been found to result from the alkaline autoxidation of catechol the same species may well be in-... 

Diones are characterized by weak fluorescence and relatively intense phosphorescence. For biacetyl, which has been investigated by many workers under a wide variety of conditions, the phosphorescence quantum yield (fa) in the gas phase 49> (27°) at 405 or 436 nm was 0.145 and the fluorescence quantum yield (fa) was 0.0023. Relative intensities (fa fa) determined in another laboratory 114> at 3650 or 4358 A (26°) were 58 ( 8) 1. This ratio decreased with increasing temperature phosphorescence was completely quenched by added oxygen 114>. 

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