Absorption, magnetic circular dichroism, IR spectra, electrochemistry, and molecular orbital calculations of monoaza- and opposite diazaporphyrins

Hiroshi Ogata, Takamitsu Fukuda, Katsunori Nakai, Yuiehi Fujimura, Saburo Neya, Pavel A. Stuzhin, Nagao Kobayashi

Research output: Contribution to journalArticlepeer-review

37 Citations (Scopus)

Abstract

Electronic absorption, magnetic circular dichroism (MCD), IR spectra, and cyclic and differential pulse voltammograms of metal-free and copper monoaza- and opposite diazaporphyrins are reported, together with molecular orbital (MO) calculations using the density functional theory (DFT) method. Introduction of nitrogen atoms at the meso position of porphyrins caused a blue-shift of the B band and a red-shift of the Q band, with a concomitant decrease and increase of the apparent absorption coefficient, respectively. On going from monoaza to diaza species, the apparent bandwidth at half-height of the B band and the splitting of the Q band do not change significantly for metal-free species, but increase for the copper species. The MCD peaks and troughs correspond closely to the peaks of the absorption spectra, so that these are interpreted as the superimposition of Faraday B terms. The MCD sign pattern (minus-to-plus on going from longer to shorter wavelengths) substantiates experimentally that the splitting between the HOMO and HOMO-1 orbital is larger than that between the LUMO and LUMO+1. Of the copper complexes of octaethylporphyrin (OEP), monoaza- (MAP), diaza- (DAP) and tetraazaporphyrins (TAP), CuTAP is the easiest to reduce and hardest to oxidize. The potential differences between the first oxidation and reduction couples were about 2.1-2.4 V. MO calculations using DFT succeeded in reproducing some of the above spectroscopic and electrochemical characteristics. In addition, some of the IR bands were assigned on the basis of the DFT calculations.

Original languageEnglish
Pages (from-to)1621-1629
Number of pages9
JournalEuropean Journal of Inorganic Chemistry
Issue number8
DOIs
Publication statusPublished - 2004 Apr 19

Keywords

  • Cyclic voltammetry
  • Density functional calculations
  • Magnetic circular dichroism
  • Porphyrinoids
  • UV
  • Vis spectroscopy

ASJC Scopus subject areas

  • Inorganic Chemistry

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