The method of similarity transformation is shown to be applicable to the problem of deterministic identifiability of photophysical kinetic models with transients. A two-state excited-state model of irreversible intermolecular association with transients is demonstrated to be identifiable from two decay traces at two observation wavelengths and one co-reactant concentration, when either only the species that associates with the co-reactant is directly excited or the excited species spectra are separated such that each species can be monitored individually. When transients are absent, two decays at one co-reactant concentration do not guarantee the recovery of the model parameters, which indicates that transient effects change identifiability criteria compared to the case with time-invariant rate constants.