Preparation, electrochemical and spectral properties of N-methylated pyridylethynyl porphyrins.
A new series of electron-deficient porphyrins were prepared by attaching one or two N-methylated 2-, 3- or 4-pyridylethynyl groups to the 10,20-meso positions of (5,15-biphenylporphinato)zinc(II). Electrochemical studies showed significant changes in the reduction potentials of these porphyrins, and N-methyl-2-pyridylethyne is the strongest electron-withdrawing substituent in the series. UV-visible spectra demonstrated largely red-shifted absorptions, and N-methyl-4-pyridylethyne has the greatest impact to the porphyrin absorptions. Electrochemical, UV-visible and EPR results concluded that porphyrins Zn2 and Zn6 reversibly undergo two one-electron porphyrin-ring reductions to their anion radicals then dianions. The first reductions of porphyrins Zn1, Zn3, Zn4 and Zn5 were irreversible one-electron transfer processes. The instability of these reduction products was suggested to result from the eletrophilic attacks at the substituents.
Lin
Ching-Yao
CY
Department of Applied Chemistry, National Chi Nan University, 302 University Road, Puli, Nantou Hsien 545, Taiwan. cyl@ncnu.edu.tw.
Chuang
Li-Chieh
LC
Yang
Ya-Fen
YF
Lin
Chun-Ling
CL
Kao
Hsien-Chang
HC
Wang
Wen-Jwu
WJ
D000042:Absorption; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D008665:Metalloporphyrins / Q000138:chemical synthesis / Q000737:chemistry; D015394:Molecular Structure; D013056:Spectrophotometry, Ultraviolet; D015032:Zinc / Q000737:chemistry*
D008665:Metalloporphyrins; D015032:Zinc