Fluorescence quenching and complexation behaviour of tetraphenylporphyrin with some divalent metal ions

The fluorescence quenching and complexation behaviour of tetraphenylporphyrin (TPP) have been studied using fluorescence, electronic absorption spectra and the stopped-flow technique. The second-order fluorescence quenching rate constant (k(q)) increases in the order Ni2+ > Co2+ > Hg2+ > Sn2+ in methanol. Both Ni2+ and Co2+ ions form relatively stable complexes with TPP and the complex formation in this case is slow. In the case of Hg2+ and Sn2+, complex formation is fast and the formed complexes are less stable compared with NiTPP and CoTPP complexes. The activation and thermodynamic parameters of the complexation process have been evaluated.