Aromatic versus antiaromatic effect on photophysical properties of conformationally locked trans-vinylene-bridged hexaphyrins

Min Chul Yoon, Sung Cho, Masaaki Suzuki, Atsuhiro Osuka, Dongho Kim

Research output: Contribution to journalArticle

70 Citations (Scopus)

Abstract

We have investigated the electronic structures and energy relaxation dynamics of vinylene-bridged hexaphyrins using steady-state and time-resolved spectroscopies along with theoretical calculations in order to reveal their aromaticity-dependent electronic and magnetic properties. Ethynyl-TIPS- substituted planar and rectangular [28]hexaphyrin, regarded as a Hü ckel antiaromatic compound, tends to adopt a twisted Möbius aromatic topology via structural distortion in order to reduce the total internal energy, in contrast to aromatic [26]hexaphyrin, which maintains a planar conformation in solution. Spectacles-shaped vinylene-bridged [26]- and [28]hexaphyrins represent highly Hückel aromatic and antiaromatic natures, respectively, as revealed by NMR spectroscopy, giving rise to remarkable differences in NICS(0) and HOMA values and shapes of steady-state absorption and emission spectra. In particular, lifetime of the lowest singlet excited state of [28]hexaphyrin (8.6 ps) is 30 times shorter than that of the aromatic congener [26]hexaphyrin (282 ps), as measured by the femtosecond transient absorption technique. Both frontier molecular orbital analyses and vertical excitation energy calculations suggest that vinylene-bridged [28]hexaphyrin has an optically dark lowest singlet state in the NIR region, as observed in the absorption spectrum with a very low oscillator strength, which might act as a ladder state in the excited-state energy relaxation dynamics. Our findings provide further insight into the aromaticity-driven electronic properties of various porphyrinoids as well as of aromatic/antiaromatic hydrocarbon systems.

Original languageEnglish
Pages (from-to)7360-7367
Number of pages8
JournalJournal of the American Chemical Society
Volume131
Issue number21
DOIs
Publication statusPublished - 2009 Jun 3

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Excited states
Electronic properties
Aromatic Hydrocarbons
Excitation energy
Aromatic hydrocarbons
Ladders
Molecular orbitals
Nuclear magnetic resonance spectroscopy
Electronic structure
Conformations
Absorption spectra
Magnetic properties
Topology
Spectroscopy
Spectrum Analysis
Magnetic Resonance Spectroscopy

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

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abstract = "We have investigated the electronic structures and energy relaxation dynamics of vinylene-bridged hexaphyrins using steady-state and time-resolved spectroscopies along with theoretical calculations in order to reveal their aromaticity-dependent electronic and magnetic properties. Ethynyl-TIPS- substituted planar and rectangular [28]hexaphyrin, regarded as a H{\"u} ckel antiaromatic compound, tends to adopt a twisted M{\"o}bius aromatic topology via structural distortion in order to reduce the total internal energy, in contrast to aromatic [26]hexaphyrin, which maintains a planar conformation in solution. Spectacles-shaped vinylene-bridged [26]- and [28]hexaphyrins represent highly H{\"u}ckel aromatic and antiaromatic natures, respectively, as revealed by NMR spectroscopy, giving rise to remarkable differences in NICS(0) and HOMA values and shapes of steady-state absorption and emission spectra. In particular, lifetime of the lowest singlet excited state of [28]hexaphyrin (8.6 ps) is 30 times shorter than that of the aromatic congener [26]hexaphyrin (282 ps), as measured by the femtosecond transient absorption technique. Both frontier molecular orbital analyses and vertical excitation energy calculations suggest that vinylene-bridged [28]hexaphyrin has an optically dark lowest singlet state in the NIR region, as observed in the absorption spectrum with a very low oscillator strength, which might act as a ladder state in the excited-state energy relaxation dynamics. Our findings provide further insight into the aromaticity-driven electronic properties of various porphyrinoids as well as of aromatic/antiaromatic hydrocarbon systems.",
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Aromatic versus antiaromatic effect on photophysical properties of conformationally locked trans-vinylene-bridged hexaphyrins. / Yoon, Min Chul; Cho, Sung; Suzuki, Masaaki; Osuka, Atsuhiro; Kim, Dongho.

In: Journal of the American Chemical Society, Vol. 131, No. 21, 03.06.2009, p. 7360-7367.

Research output: Contribution to journalArticle

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T1 - Aromatic versus antiaromatic effect on photophysical properties of conformationally locked trans-vinylene-bridged hexaphyrins

AU - Yoon, Min Chul

AU - Cho, Sung

AU - Suzuki, Masaaki

AU - Osuka, Atsuhiro

AU - Kim, Dongho

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