Impact of Zn2+ introduced into the central cavity of meso-tetra(4-pyridyl)porphine on its spectroscopic features

Abstract The effect of metal ion (Zn2+) introduced into the center cavity of macrocyclic meso-tetra(4-pyridyl)porphine, H2TPyP, on its spectroscopic feature is explored. Thin films of H2TPyP and ZnTPyP are successfully prepared using the thermal evaporation technique. The linear and nonlinear spectroscopic characterizations of H2TPyP and ZnTPyP films are investigated as comparative study. Our results indicate that some perturbations in the absorption spectroscopy of the H2TPyP due to Zn complexation to form ZnTPyP led to reduce four quasi degenerated Q-bands to two Q-bands and in addition to the Soret (B) band splits into two sub-bands (Bx & By) called Davydov splitting. The indirect allowed transition dominated the electronic absorption bands for both H2TPyP and ZnTPyP films and the values of optical band gap enhanced due to metalation of H2TPyP into ZnTPyP. A single oscillator model is applied to normal dispersion behavior of refractive index spectrum for H2TPyP and ZnTPyP films and from which, the dispersion parameters are calculated and exhibited an increased in their values due to insertion of Zn atom into H2TPyP. The nonlinear optical parameters such as third order susceptibility (χ(3)), nonlinear refractive index (n2) and nonlinear absorption coefficient (βc) are derived from dispersion parameters and showed a decrease in their values for ZnTPyP films with respect to H2TPyP films due to the introduction of Zn atom in central cavity of porphyrin macrocycle.