Methoxy-isoporphyrins of water-soluble porphyrins: synthesis, characterization and electrochemical properties

Abstract

Methoxy-isoporphyrins of zinc [5,10,15,20-tetrakis(4-sulfonatophenyl)]porphyrin, ZnTSPP (1a) and zinc [5,10,15,20-tetrakis(4-carboxyphenyl)]porphyrin, ZnTCPP (1b) have been synthesized and characterized using standard spectroscopic techniques (Uv-visible, ¹H NMR) , ESI-mass spectrometry and powder X-ray diffraction studies. The isoporphyrins [5-(methoxy)-5,10,15,20-tetrakis(4-sulfonatophenyl)-5H,15H-porphinato]zinc(II) (2a) and [5-(methoxy)-5,10,15,20-tetrakis(4-carboxyphenyl)-5H,21H-porphinato]zinc(II) (2b) are formed due to nucleophilic attack of the methanol to the zinc porphyrin dication. Ceric ammonium nitrate (CAN) was used to oxidize zinc porphyrin and to form zinc porphyrin dication. The electronic spectra of the isoporphyrin complexes 2a and 2b exhibit an intense peak at near IR region . Electrochemical measurements of the synthesized isoporphyrins showed a typical irreversible reduction peak at lower potential. S-containing nucleophiles, which work as reducing agents, convert the zinc isoporphyrins to their parent porphyrins, which supports the electrochemical observations. Their structural properties have been studied using powder X-ray diffraction. The luminescence properties of isoporphyrins were compared with the parent zinc porphyrins.

Graphical Abstract

Keywords:

• Porphyrin
• zinc
• electronic spectroscopy
• electrochemistry
• powder X-ray diffraction

Acknowledgement

Authors are thankful to DST-FIST in Physics Department, NERIST for powder Xrd facility, head SAIF, NEHU, Shillong for the ¹H NMR data and to Dr. Md. Harunar Rashid, Department of Chemistry, Rajiv Gandhi University, Doimukh, Arunachal Pradesh for extending the use of the fluorescence spectrophotometer.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

JB acknowledges SERB, DST, New Delhi for the start-up grant (YSS/2015/000394).