Unraveling Excited-Singlet-State Aromaticity via Vibrational Analysis

Juwon Oh, Young Mo Sung, Hirotaka Mori, Seongchul Park, Kjell Jorner, Henrik Ottosson, Manho Lim, Atsuhiro Osuka, Dongho Kim

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

The concept of excited-state aromaticity is receiving much attention in that completely reversed aromaticity in the excited state (so-called aromaticity reversal) provides crucial insight into photostability, photoreactivity, and its application to the photosynthetic mechanism and photoactive materials. Despite this significance, experimental elucidation of excited-state aromaticity is still unsolved, particularly for the excited singlet state. Here, as an unconventional approach, time-resolved IR (TRIR) spectroscopy on aromatic and anti-aromatic hexaphyrin congeners shed light on excited-singlet-state aromaticity. The contrasting spectral features between the Fourier transform IR and TRIR spectra reveal the aromaticity-driven structural changes, corroborating aromaticity reversal in the excited singlet states. Our paradigm for excited-state aromaticity, the correlation of IR spectral features with aromaticity reversal, provides another fundamental key to understanding the role of (anti)aromaticity in the stability, dynamics, and reactivity in the excited singlet state of π-conjugated molecular systems. Whereas ground-state aromaticity governs molecular properties, excited-state aromaticity can not only rationalize photostability and photoreactivity but also offer fruitful insight into designing photoactive materials. However, evaluation of excited-state aromaticity is still challenging and elusive, particularly for excited singlet states, because estimating aromaticity with conventional magnetic and energetic indices is still inaccessible to transient excited states. As an unconventional approach, time-resolved IR spectroscopy, which offers information on structural changes in photoreactions, can facilitate a study of excited-state aromaticity. As reported here, IR spectral changes allow us to monitor the change in vibrational modes and structural distortions in the excited singlet state, which is correlated with aromaticity changes. This report opens another avenue for unraveling excited-state aromaticity and its application to photosynthetic protocols and photoactive materials. Kim and colleagues employed time-resolved IR (TRIR) spectroscopy to scrutinize excited-singlet-state aromaticity from the viewpoint of molecular geometry. The interconvertible spectral features were observed in the IR spectra between the ground and excited singlet states; the contrasting spectral features of simple and complicated Fourier transform IR spectra between aromatic and anti-aromatic hexaphyrins were reversed in their TRIR spectra. Qualitative analyses revealed that the interconvertible spectral features arise from aromaticity-driven structural changes, demonstrating aromaticity reversal in the excited singlet states.

Original languageEnglish
Pages (from-to)870-880
Number of pages11
JournalChem
Volume3
Issue number5
DOIs
Publication statusPublished - 2017 Nov 9

Fingerprint

Excited states
structural change
Spectrum Analysis
spectroscopy
Fourier Analysis
Fourier transform
Photoreactivity
energetics
analysis
Infrared spectroscopy
geometry
Fourier transforms
material
Ground state

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Biochemistry
  • Environmental Chemistry
  • Chemical Engineering(all)
  • Biochemistry, medical
  • Materials Chemistry

Cite this

Oh, J., Sung, Y. M., Mori, H., Park, S., Jorner, K., Ottosson, H., ... Kim, D. (2017). Unraveling Excited-Singlet-State Aromaticity via Vibrational Analysis. Chem, 3(5), 870-880. https://doi.org/10.1016/j.chempr.2017.09.005
Oh, Juwon ; Sung, Young Mo ; Mori, Hirotaka ; Park, Seongchul ; Jorner, Kjell ; Ottosson, Henrik ; Lim, Manho ; Osuka, Atsuhiro ; Kim, Dongho. / Unraveling Excited-Singlet-State Aromaticity via Vibrational Analysis. In: Chem. 2017 ; Vol. 3, No. 5. pp. 870-880.
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Oh, J, Sung, YM, Mori, H, Park, S, Jorner, K, Ottosson, H, Lim, M, Osuka, A & Kim, D 2017, 'Unraveling Excited-Singlet-State Aromaticity via Vibrational Analysis', Chem, vol. 3, no. 5, pp. 870-880. https://doi.org/10.1016/j.chempr.2017.09.005

Unraveling Excited-Singlet-State Aromaticity via Vibrational Analysis. / Oh, Juwon; Sung, Young Mo; Mori, Hirotaka; Park, Seongchul; Jorner, Kjell; Ottosson, Henrik; Lim, Manho; Osuka, Atsuhiro; Kim, Dongho.

In: Chem, Vol. 3, No. 5, 09.11.2017, p. 870-880.

Research output: Contribution to journalArticle

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AU - Sung, Young Mo

AU - Mori, Hirotaka

AU - Park, Seongchul

AU - Jorner, Kjell

AU - Ottosson, Henrik

AU - Lim, Manho

AU - Osuka, Atsuhiro

AU - Kim, Dongho

PY - 2017/11/9

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N2 - The concept of excited-state aromaticity is receiving much attention in that completely reversed aromaticity in the excited state (so-called aromaticity reversal) provides crucial insight into photostability, photoreactivity, and its application to the photosynthetic mechanism and photoactive materials. Despite this significance, experimental elucidation of excited-state aromaticity is still unsolved, particularly for the excited singlet state. Here, as an unconventional approach, time-resolved IR (TRIR) spectroscopy on aromatic and anti-aromatic hexaphyrin congeners shed light on excited-singlet-state aromaticity. The contrasting spectral features between the Fourier transform IR and TRIR spectra reveal the aromaticity-driven structural changes, corroborating aromaticity reversal in the excited singlet states. Our paradigm for excited-state aromaticity, the correlation of IR spectral features with aromaticity reversal, provides another fundamental key to understanding the role of (anti)aromaticity in the stability, dynamics, and reactivity in the excited singlet state of π-conjugated molecular systems. Whereas ground-state aromaticity governs molecular properties, excited-state aromaticity can not only rationalize photostability and photoreactivity but also offer fruitful insight into designing photoactive materials. However, evaluation of excited-state aromaticity is still challenging and elusive, particularly for excited singlet states, because estimating aromaticity with conventional magnetic and energetic indices is still inaccessible to transient excited states. As an unconventional approach, time-resolved IR spectroscopy, which offers information on structural changes in photoreactions, can facilitate a study of excited-state aromaticity. As reported here, IR spectral changes allow us to monitor the change in vibrational modes and structural distortions in the excited singlet state, which is correlated with aromaticity changes. This report opens another avenue for unraveling excited-state aromaticity and its application to photosynthetic protocols and photoactive materials. Kim and colleagues employed time-resolved IR (TRIR) spectroscopy to scrutinize excited-singlet-state aromaticity from the viewpoint of molecular geometry. The interconvertible spectral features were observed in the IR spectra between the ground and excited singlet states; the contrasting spectral features of simple and complicated Fourier transform IR spectra between aromatic and anti-aromatic hexaphyrins were reversed in their TRIR spectra. Qualitative analyses revealed that the interconvertible spectral features arise from aromaticity-driven structural changes, demonstrating aromaticity reversal in the excited singlet states.

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Oh J, Sung YM, Mori H, Park S, Jorner K, Ottosson H et al. Unraveling Excited-Singlet-State Aromaticity via Vibrational Analysis. Chem. 2017 Nov 9;3(5):870-880. https://doi.org/10.1016/j.chempr.2017.09.005