Electronic structures of azulene-fused porphyrins as seen by magnetic circular dichroism and TD-DFT calculations

Katsunori Nakai, Kei Kurotobi, Atsuhiro Osuka, Masanobu Uchiyama, Nagao Kobayashi

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

A combination of magnetic circular dichroism (MCD), electronic absorption spectroscopy and time-dependent density functional theory (TD-DFT) calculations has been used to investigate the electronic structure of azulene-fused π-expanded porphyrins based primarily on the spectral properties of absorption bands in the near infrared region. From MCD experiments, it was suggested that in the case of a mono-azulene-fused porphyrin ΔHOMO ≃ ΔLUMO (where ΔHOMO is the magnitude of the energy gap between the HOMO and HOMO-1 and ΔLUMO is the magnitude of the energy gap between the LUMO and LUMO+1), while in the case of an oppositely-di-azulene-fused porphyrin, ΔHOMO < ΔLUMO. Since Faraday A terms are observed for both the Soret and Q bands in the MCD spectrum of tetra-azulene-fused porphyrin the corresponding excited states are clearly accidentally degenerate despite the C2 molecular symmetry. Transition dipole moment analysis clearly demonstrates that the electronic absorption spectrum of tetra-azulene-fused porphyrin has out-of-plane electronic transitions slightly to the blue of the main Q and Soret bands. Comparison with distorted porphyrins and phthalocyanines strongly suggests that these out-of-plane transitions appear as intense Gaussian-shaped Faraday B terms in the MCD spectra.

Original languageEnglish
Pages (from-to)466-471
Number of pages6
JournalJournal of Inorganic Biochemistry
Volume102
Issue number3
DOIs
Publication statusPublished - 2008 Mar 1

Keywords

  • Azulene
  • Magnetic circular dichroism
  • Porphyrin
  • TD-DFT

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry

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