IS IT REALLY THE JABLONSKI DIAGRAM?

Alexander A. Krasnovsky (deceased 1993)

A.N. Bach Institute of Biochemistry
Moscow, Russian Federation

Some question the common practice of referring to the figure showing singlet and triplet states as a Jablonski Diagram (see the module on Basic Photophysics). They point out that Jablonski did not propose a triplet manifold of states to explain phosphorescence (delayed fluorescence), a phenomenon distinct from fluorescence.

Perrin was the first to claim the existence of a metastable state between the ground and fluorescent states of dyes. He proposed that thermal activation of this state is a reason for the appearance of delayed fluorescence of dyes. (Perrin F. Ann. Phys. (Paris) 12, 169, 1929).

A few years latter Jablonski developed this idea. He proposed that radiative transition from the metastable to the ground state is a reason for low-temperature phosphorescence of dyes (A. Jablonski. Nature 131, 839, 1933; Z. Physik. 94, 38, 1935). Thus, Jablonski became an author of the modern scheme of radiative transitions in dye molecules. However, neither Perrin nor Jablonski, understood the nature of the metastable state.

Kautsky noticed that delayed fluorescence and phosphorescence are quenched much more strongly by oxygen than is the fluorescence of dyes. Therefore, he proposed that the metastable state might be an important intermediate in photooxygenation reactions (H. Kautsky. Trans. Farad. Soc. 35, 216-219, 1939). Frank and Livingston proposed that this metastable state could be responsible for a variety of photochemical and photobiological reactions (J. Frank and R. Livingston. J. Chem. Phys. 9, 184-190, 1941).

The idea that the metastable state is a triplet state was first proposed by A.N. Terenin (Acta Physico-chinica USSR, 18, No 4, 210- 241, 1943), and G.N. Lewis and M. Kasha (J. Am. Chem. Soc. 66, 2100-2116, 1944). The fluorescence state was defined to be a singlet state. In both papers, the authors claimed that the triplet state (due to a much longer lifetime) might be a more efficient promotor of photochemical reactions than the singlet state. Hence, the diagram often referred to as a Jablonski diagram, is really a Perrin-Jablonski diagram modified by Terenin and Lewis-Kasha.

Relevant Reference:
C.A. Parker. Photoluminescence of Solutions, Elsevier, 1968, p. 44.

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