EXCITED SINGLET-STATE PROTOTROPISM OF 9-PHENANTHROL

The actual dependence of fluorescence spectrum of an excited acid or base upon pH is determined by rates of proton exchange and rates of fluorescence. The stretched sigmoid curves obtained from fluorimetric titration of 9-phenanthrol and its anion indicate that the rates of excited-state proton exchange are comparable to the rates of deactivation of the conjugated pair. Here I analyse these curves using the lifetimes of both species, and compare the excited-state equilibrium constant obtained from the rate constants and the equilibrium constants determined by other methods.