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Protonated [4n]pi and [4n+2]pi octaphyrins choose their Möbius/Hückel aromatic topology.

Authors
  • Lim, Jong Min
  • Shin, Jae-Yoon
  • Tanaka, Yasuo
  • Saito, Shohei
  • Osuka, Atsuhiro
  • Kim, Dongho
Type
Published Article
Journal
Journal of the American Chemical Society
Publisher
American Chemical Society
Publication Date
Mar 10, 2010
Volume
132
Issue
9
Pages
3105–3114
Identifiers
DOI: 10.1021/ja909744z
PMID: 20148589
Source
Medline
License
Unknown

Abstract

Protonation-triggered conformational changes of meso-octakis(pentafluorophenyl) [36]octaphyrin and [38]octaphyrin have been investigated. The X-ray crystal structures and (1)H NMR analyses revealed that the protonation process cuts off intramolecular hydrogen bonds between aminic and iminic pyrrole units and, at the same time, produces intermolecular hydrogen-bond network between aminic pyrrole unit and counter-anions. Such a replacement induces some pyrrole inversion, leading to Mobius aromatic conformation for [36]octaphyrin and to Huckel aromatic conformation for [38]octaphyrin. These protonated octaphyrins show similar structures only with a subtle difference in tilted pyrrole angles, which results in their different topologies. This feature strongly suggests that the macrocycles control their topologies by pyrrole rotation to gain [4n]pi Mobius or [4n+2]pi Huckel aromatic stabilization, depending on the number of pi-electrons. Detailed photophysical properties such as absorption/fluorescence, excited singlet/triplet state lifetimes, and two-photon absorption cross-section values have been presented for both protonated [36] and [38]octaphyrins in conjunction with their Mobius or Huckel aromaticity.

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