Kinetics and Equilibria of Excited State Protonation Reactions

KINETICS AND EQUILIBRIA OF EXCITED STATE PROTONATION REACTIONS 

In the earlier work (Forster, 1951 Weller, 1952) when the principal experimental information involved fluorescence intensities, the most useful algebraic expressions were those relating relative quantum yields of the conjugate acid base pair to the solution acidity. In favourable cases such expressions were used to obtain rate constants for the forward and reverse reactions, and hence equilibrium constants, though it was always necessary to make allowance 

The groundwork for the solution of the types of problem encountered was laid by Forster (1951) and Weller (1952, 1954, 1957a, 1957b, 1958a, 1958c, 1961) and some examples will now be given to illustrate their method of approach. 

BH+(Sj) and B(SX), the protonated and unprotonated base species in the Sx state, will be represented by and y respectively, and the rate constant suffixes denote transitions to the ground state by solvent and other quenching (q), and by fluorescence (f), or transitions by intersystem crossing to the triplet state (T). Primed constants refer to the base species B(SX) and unprimed to the conjugate acid BH+(S ). In the protonation equilibrium the rate 

Clearly, in cases in which only BH+ or B is excited (and no instantaneous conversion takes place before the steady state is set up), (15) and (16) are considerably simplified by setting x0 = 0 or y0 = 0. In specific cases the use of justifiable simplifications about the magnitudes of the components of a and a can simplify the expressions still further. For example, if y0 = 0 and the pH is high enough for k2 to be very small compared with all the other rate 

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Kinetics and Equilibria of Excited State Protonation Reactions. ... 

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