Microscale Synthesis and Electronic Absorption Spectroscopy of Tetraphenylporphyrin H2(TPP) and Metalloporphyrins ZnII(TPP) and NiII(TPP)

The microscale syntheses of Tetraphenylporphyrin, H 2 (TPP), and the corresponding metalloporphyrins Zn II (TPP) and Ni II (TPP) are reported. H 2 (TPP) is synthesized by the condensation of benzaldehyde and pyrrole, and the subsequent metallation of H 2 (TPP) is achieved with anhydrous Zn II Cl 2 or Ni II Cl 2 in DMF. The compounds are analyzed by their electronic absorption spectra in the visible region, and by their fluorescence properties. The visible spectra are obtained on a Spectronic 20 spectrophotometer. Analysis of the electronic absorption spectra is presented on the basis of Zn II (TPP) representing the class of regular metallporphyins, and Ni II (TPP) representing the class of hypsoporphyrins. The hypsochromic (blue) shifts of the Ni II (TPP) complex is discussed in terms of significant metal to ligand pi-backbonding. A group theoretical interpretation of the simplified electronic absorption spectra of the metalloporphyrins of D 4h symmetry, relative to the free-base porphyrin H 2 (TPP) of D 2h symmetry is offered.