N-confused meso-tetraaryl-substituted free-base porphyrins: determination of protonation and deprotonation constants in nonaqueous media

作者：Ou Zhongping^*; Chen Xueyan; Ye Lina; Xue Songlin; Fang Yuanyuan; Jiang Xiaoqin; Kadish Karl M

来源：Journal of Porphyrins and Phthalocyanines, 2015, 19(1-3): 251-260.

DOI：10.1142/S1088424614501132

• N-confused free-base porphyrins
• protonation
• deprotonation
• determination of equilibrium constants

The protonation and deprotonation reactions for a series N-confused meso-tetraarylsubstituted free-base porphyrins containing electron-donating or electron-withdrawing substituents was monitored in CHCl3 and DMF by UV-visible spectroscopy during titrations with trifluoroacetic acid or tetra-n-butylammonium hydroxide. The spectroscopic data was also used to calculate equilibrium constants for these reactions. The examined compounds are represented as (XPh)(4)NCPH2, where "NCP" represents the N-confused porphyrin p-conjugated macrocycle and X is a CH3O, CH3, H or Cl para-substituent on the four meso-phenyl rings (Ph) of the compound. The porphyrins can exist in two tautomeric forms depending upon the solvent and each tautomer undergoes two stepwise protonation reactions leading to formation of the mono-and bis-protonated porphyrins, [(XPh)(4)NCPH3](+) and [(XPh)(4)NCPH4](2+). A single step deprotonation is observed for the same compounds in DMF and the product is assigned as [(XPh)(4)NCPH](-). Comparisons are made between UV-visible spectra of the protonated, neutral and deprotonated forms of the porphyrin and the effect of the porphyrin ring substituents and tautomeric form of the neutral porphyrin on the UV-visible spectra and protonation constants is discussed along with data from DFT calculations.

• 出版日期2015-3