EXCITED STATE EQUILIBRATION AND THE FLUORESCENCE-ABSORPTION RATIO.

Robert S. Knox,

University of Rochester, Rochester, NY 14627-0171 USA
(e-mail: rsk@pas.rochester.edu; Fax: (716) 242 0851)

Ideally, in any system the fluorescence and absorption spectra are connected by a simple relation.  Essentially, F, the logarithm of their ratio at a given frequency is a decreasing function of photon frequency, with slope proportional to the inverse ambient temperature [1-4].  Ideal circumstances include excited state thermal equilibration.  Although impossible in principle because of finite lifetimes, this is often approximated in that F is often nearly linear (example: [5]). An effective temperature [6], defined locally on F, seems a very sensitive detector of deviations from linearity and, we believe, from equilibrium in the excited state.  Plots of this temperature display various features.  Peaks can be shown to be characteristic of slow equilibration between two internally well-equilibrated excited manifolds [6,7].  A chlorophyll-a anomaly [8] can be analyzed on this model, indicating a previously unnoticed weakly fluorescent state.  The case of chlorophyll and many others will be included in a general review of the application of the universal relation to studies of fluorescent systems.
(Supported by USDA grant NRICGO-95-37306 and by NSF grants 94-00059, 94-15583)

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5. See, e. g., J. Hevesi, L. Kozma, and L. Szalay (1966), Acta Phys. Polonica 29, 57-64
6. D. A. Sawicki and R. S. Knox (1996), Phys. Rev. A 54, 4837-4841
7. R. S. Knox (1997), Pure and Appl. Chem. 69, 1163-1170
8. R. S. Knox, P. D. Laible, D. A. Sawicki, and M. F. J. Talbot (1997), J. Luminescence 72-74, 580-581