Z-scan studies and quantum chemical calculations of meso-tetrakis(p-sulfonatophenyl)porphyrin and meso-tetrakis(4-N-methyl-pyridiniumyl)porphyrin and their Fe(III) and Mn(III) complexes
✍ Scribed by I. E. Borissevitch; A. G. Bezerra- Jr,; A. S. L. Gomes; R. E. de Araújo; B. Cid de Araújo; K. M. T. Oliveira; M. Trsic
- Publisher
- John Wiley and Sons
- Year
- 2001
- Tongue
- English
- Weight
- 93 KB
- Volume
- 05
- Category
- Article
- ISSN
- 1088-4246
No coin nor oath required. For personal study only.
✦ Synopsis
Optical self-defocusing, characterized by the non-linear refractive index n~2~, was investigated by the Z-scan technique in water solutions of two porphyrins (PPhs), negatively charged meso-tetrakis(p-sulfonatophenyl)porphyrin ( TPPS ~4~) and positively charged meso-tetrakis(4-N-methyl-pyridiniumyl)porphyrin ( TMPyP ), in their free base forms and as Fe (III) and Mn (III) complexes. Significant n~2~ values were observed only for the TMPyP metal complexes, while for the other porphyrins the n~2~ values were negligible. The effect is explained by the reorientation of the porphyrin molecule due to interaction of its permanent dipole moment perpendicular to the molecular ring plane with the electromagnetic field of the exciting light pulse. The permanent dipole moment is due to the shift of the metal atom out of the molecular plane. The electrostatic interaction between the metal atom and charged substituents increases (repulsion) or decreases (attraction) the shift of the metal atom and consequently affects the dipole moment value. Ligand binding to the metal atoms also increases the out-of-plane metal shift and hence the dipole moment and n~2~ value. pH changes were shown to modify the Fe (III)-ligand structure, thus changing n~2~. The experimental data correlate well with the metal shift and dipole moment values calculated for simplified PPh structures by the ZINDO method.