Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1238452 | Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy | 2007 | 6 Pages |
Abstract
The spectrophotometric titration by sodium hydroxide of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin ((OH)1PH2) is studied as a function of solvent composition of DMF-H2O binary solvent mixture ([OHâ]Â =Â 0.04Â M). Combining the structure changes of the porphyrin and the “four orbital” model of Gouterman, many features of the optical spectra of this deprotonated para-hydroxy-substituted tetraphenylporphyrin in different composition of binary solvent mixtures can be rationalized. In highly aqueous solvents, the changes of the titration curves are shown to be mainly due to hydrogen-bonding of the oxygen of the phenoxide anion group by the hydroxylic solvent, Which decreases the energy of the phenoxide anion Ï orbital. Thus the phenoxide anion Ï orbital cannot cross over the porphyrin Ï orbital being a different HOMO. However, its energy is close to that of the porphyrin Ï orbitals. As a result, in the visible region, no charge-transfer band is observed, while in the visible-near region, the Soret peak split into two components. In nonaqueous solvents, the changes are mainly attributed to further deprotonation of pyrrolic-Hs of (OH)1PH2 by NaOH and coordination with two sodium ions to form the sodium complex of (OH)1PH2, which turns hyperporphyrin spectra of deprotonated of phenolic-H of (OH)1PH2 into three-banded spectra of regular metalloporphyrin.
Related Topics
Physical Sciences and Engineering
Chemistry
Analytical Chemistry
Authors
Hongwei Guo, Junguang Jiang, Yingyan Shi, Yuling Wang, Shaojun Dong,