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Journal of Spectroscopy
Volume 2013, Article ID 713745, 7 pages
Research Article

Effects of Core and/or Peripheral Protonation of meso-Tetra(2-, 3-, and 4-pyridyl)Porphyrin and meso-Tetra(3-methylpyridyl)Porphyrin on Their UV-vis Spectra

1Department of Chemistry, Institute for Advanced Studies in Basic Sciences, Zanjan 45137-66731, Iran
2School of Chemistry, Damghan University, Damghan 36716-41167, Iran

Received 11 June 2012; Revised 19 July 2012; Accepted 20 July 2012

Academic Editor: Christophe Dujardin

Copyright © 2013 Saeed Zakavi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Core and/or peripheral protonation of meso-tetra(pyridyl)porphyrins, H2(py)P, with weak and strong acids have been studied by UV-vis spectroscopy. The results support the proposal that the position of the Soret as well as the Q(0,0) bands of the dications is influenced by π donation from the meso substituents to the porphyrin core. The red shift of the Q(0,0) band of H2t(py)P dications with 2-, 3-, and 4-pyridyl substituents does not correlate with the order of π electron donor ability of the meso groups. The decreased electron donation from the central nitrogen atoms to the acids on going from 3-pyridyl group to 4- and 2-pyridyl ones has been used to explain this observation. In spite of the negative effect of N-methylation of pyridyl substituents on the basicity of the central nitrogen atoms of meso-tetra(3-methylpyridyl)porphyrin, H2t(3-Mepy)P, protonation of H2t(3-Mepy)P occurs with weak and strong acids. The blue shift of the Q(0,0) bands upon protonation of H2t(3-Mepy)P with weak and strong acids clearly shows the importance of resonance interactions between the π-systems of porphyrin and the aryl substituents on the position of the band.