The photophysical properties of photochromic spirodihydro-indolizines (DHI) with podand structures can be tuned by selective cation binding. Complexation of alkaline earth metal ions by the DHI provokes changes in the electronic states of the host molecules, which is evident in changes in the absorption spectra. Thus binding constants could be determined by uv spectroscopy. Two methods have been used to evaluate the titration data : The double-reciprocal Benesi- Hildebrand plot and the direct fit of the observation equation by nonlinear least-squares analysis.