title: Solvent effects on spectrophotometric titrations and vibrational spectroscopy of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin in aqueous DMF.
abstract: The spectrophotometric titration by sodium hydroxide of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin ((OH)(1)PH(2)) is studied as a function of solvent composition of DMF-H(2)O binary solvent mixture ([OH(-)]=0.04 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 pi orbital. Thus the phenoxide anion pi orbital cannot cross over the porphyrin pi orbital being a different HOMO. However, its energy is close to that of the porphyrin pi 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)(1)PH(2) by NaOH and coordination with two sodium ions to form the sodium complex of (OH)(1)PH(2), which turns hyperporphyrin spectra of deprotonated of phenolic-H of (OH)(1)PH(2) into three-banded spectra of regular metalloporphyrin.
authors.affiliation: State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, PR China.
authors.forename: Hongwei
authors.initials: H
authors.lastname: Guo
authors.forename: Junguang
authors.initials: J
authors.lastname: Jiang
authors.forename: Yingyan
authors.initials: Y
authors.lastname: Shi
authors.forename: Yuling
authors.initials: Y
authors.lastname: Wang
authors.forename: Shaojun
authors.initials: S
authors.lastname: Dong
mesh_terms: D004126:Dimethylformamide / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011166:Porphyrins / Q000737:chemistry*; D012997:Solvents; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water
chemical_list: C522489:5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin; D011166:Porphyrins; D012997:Solvents; D014867:Water; C042331:N-hydroxymethyl-N-methylformamide; D004126:Dimethylformamide