High pressure luminescence of metalloporphyrins in liquid solution

High pressure luminescence measurements have been made on free-metal tetraphenyl-porphyrin (H2-TPP), as well as on Mg-TPP, Zn-TPP, and cuoctaethylporphyrin Cu-OEP, in a variety of organic liquid media. Radiative and nonradiative rates have been calculated as function of pressure for all compounds studied. It has been shown that the changes of the radiative rates are due to the change of the square of the refractive index with pressure. In the case of H2-TPP, Mg-TPP, and Zn-TPP only fluorescence was observed and the nonradiative rates are determined by viscosity. In the case of Cu-OEP only phosphorescence was detected from two states (2T1 and 4T1). The relative energies of these two excited states have been found to be pressure dependent. The radiationless rate 4T1→S0 scaled very well with the 4T1→S0 energy difference, while the intersystem crossing rate 2T1→4T1 is controlled by the 2T1→4T1 energy gap. Solvents which freeze at intermediate pressure have been also used in order to study the effects of the phase transition on the luminescence of the compounds studied