No abstract

Under experimental conditions in which the interaction between triplet dye and oxygen is an initiating process (D–O mechanism), the photosensitized oxidation of leucofluorescein in the aqueous solution (reaction (1)) has been found to decrease in rate with the increasing oxygen concentration and that the magnitude of the retarding effect of oxygen is almost the same independent of sensitizing dye. This is in sharp contrast to the kinetic feature of the oxidative photobleaching of dye (reaction (2)), where the rate becomes constant beyond a certain small oxygen concentration. On the basis of these findings, it has been proposed that in reaction (1), 1O2 plays a dominant role and it is deactivated by process 1O2+3O2→23O2. As to reaction (2), strong evidence has been presented for the view that the interaction of triplet dye and oxygen in the aqueous solution produces a rather stable D+···O2− of which only a small portion decomposes irreversibly. The principal evidence is as follows; 1) the free half-oxidized dye (produced by the reaction between triplet dye and [Co(Ox)3]3− was found to oxidize FH2 with a high rate and its decay was found to be accelerated by the addition of FH2; 2) the decay of the half-oxidized species (first order decay!) produced in the aerated aqueous solution, on the other hand, was not affected by FH2 under otherwise similar conditions as in (1).

No abstract

Th effect of inorganic anions on the dimerization constant of pyronine G in an aqueous solution was examined. It was found that the effect is very specific and can not be explained simply by the effect of the ionic strength. The analysis led to the conclusion that a dimer exists as an ion-pair with the anions attached laterally to dye ions instead of being sandwiched between two dye ions. The change of absorption spectra in the alkaline solution was interpreted to be due to the formation of carbinol, and from its analysis the formation constant of carbinol was determined. Carbinol was found to have also its proper fluorescence, and from the pH change of fluorescence spectra the formation constant of carbinol was again decided, the value of which coincided well with that obtained from the absorption spectra.

Fluorescence yields of azulene derivatives with various kinds of substituents were determined in cyclohexane at room temperature. Most of them were found to emit fluorescence from the second excited state. In particular, 1,3‐dichloroazulene emits fluorescence which is twice as efficient as that of azulene. The quantum yield of “anomalous fluorescence” was found to be sufficiently well correlated with the energy gap δE between the first and the second excited states and to decrease with the decrease in δE. The rate constant of radiationless transition was calculated from the fluorescence yield and the calculated radiative lifetime. The rate constant was found to increase exponentially with decreasing δE. It was concluded that the internal conversion to the first excited state is the main route of the radiationless decay of the second excited state of azulene and its derivatives. Some discussions are given concerning the skeletal stretching modes as possible acceptors of the electronic energy upon the internal conversion S2∼→S1.