Fluorescence depolarization of solutions and ordered systems. Photochemical reactions in the excited states. II. General considerations (b)

A theory of time-resolved polarized fluorescence spectroscopy of photoreactive molecules is discussed. This theory is applicable to solutions as well as to ordered molecular systems. The approach discussed differentiates the physico-chemical properties of molecules in ground, initially excited and in relaxed excited states, by assuming the state-dependent alignment interactions and rotational dynamics of solute molecules and their photoproducts. Such cases as state-dependent geometrical transformations of solutes and their photoproducts as well as orientation-dependent rates for state-to-state kinetic relaxation are also discussed. It is also shown that in the case of flexible fluorophores dissolved in an ordered system the measurements of polarization-free signals can provide information on their aligning properties and rotational dynamics within an ordered environment. The theory presented in this article is directed to the problem of application of polarized fluorescence spectroscopy in multidimensional molecular photochemistry. It can also be used in studies of biological systems as well as in studies of media properties as probed by photoreactive molecules of known photochemical properties.