IDENTIFIABILITY OF IRREVERSIBLE INTERMOLECULAR 2-STATE EXCITED-STATE PROCESSES

This report analyzes which kinetic and spectral parameters can be reco vered by global compartmental analysis for intermolecular two-state ex cited-state processes when k(21)[M] (Scheme 1) is negligible. The time -resolved fluorescence of such a photophysical system will decay as a biexponential function with invariant decay times. The ratio of the am plitudes associated with the decay times will depend on [M]. Although the association rate constant k(21) is known to be zero, this knowledg e is not helpful in determining unique values for the remaining parame ters. It is shown that the available information which can be derived from time-resolved fluorescence data only is strongly limited. When k( 12) is not negligible, the values of k(01), (k(02) + k(12)), and the r elation connecting k(12) and the ground-state dissociation constant ca n be obtained from two decay traces collected for two different concen trations of M. For such a system it is impossible to determine the gro und-state dissociation constant from time-resolved fluorescence measur ements exclusively. The identifiability analysis shows that additional decay curves measured at different concentrations of M and excitation or emission wavelengths do not provide independent information useful for the unique determination of the remaining parameters. If the grou nd-state dissociation constant can be obtained from fluorimetric titra tion, the photophysical system becomes identifiable. In the limiting c ase when k(12) = 0, the relation between k(12) and the ground-state di ssociation constant vanishes. The addition of quencher to intermolecul ar two-state excited-state processes when k(21)[M] is negligible does not provide additional information useful for the unique determination of the kinetic and spectral parameters.