Comparative studies on energy relaxation dynamics of directly linked ZnII porphyrin dimers with different dihedral angles

Hyun Sun Cho, Jae Kyu Song, Jeong Hyon Ha, Sung Cho, Dongho Kim, Naoya Yoshida, Atsuhiro Osuka

Research output: Contribution to journalArticle

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Abstract

Photophysical properties of the strapped ZnII porphyrin dimers (Sn, the strap chain between the porphyrins changes; -O-(CH2)n-O-, n = 1, 2, 3, 4, 8, and 10) and directly linked ZnII porphyrin dimer (Z2) have been investigated by the steady-state and time-resolved spectroscopic methods. The reduced dihedral angle in Sn gives rise to additional absorption bands around 400 nm as well as broad fluorescence in the near-infrared region. The fluorescence lifetimes of Sn become gradually, but not so significantly, shorter as the strap length becomes shorter, indicating that the lifetimes of the lowest excited singlet states of Sn are not affected much despite their structural distortions such as mean plane deviations and the existence of two conformers. Fluorescence excitation and viscosity-dependent fluorescence spectra suggest that S2 exists as two conformers. A and B conformer, which has been also confirmed by X-ray data. The B conformer with a shorter interporphyrin distance has stronger interporphyrin interactions than the A conformer, which was revealed by the fluorescence excitation and fluorescence spectra. The A conformer is responsible for the shorter wavelength fluorescence at ca. 660 nm, whereas the B conformer gives rise to the near-infrared fluorescence. The photoinduced near-infrared absorption band was suggested to be characteristic of S2, which was not observed in Z2. The conformational dynamics of S2 with a time constant of 15 ps was observed in the transient absorption and fluorescence upconversion measurements. From the comparative studies of Z2 and Sn, we have demonstrated that the orientation of the two porphyrin macrocycles has a considerable effect on their photophysical properties.

Original languageEnglish
Pages (from-to)1897-1903
Number of pages7
JournalJournal of Physical Chemistry A
Volume107
Issue number12
DOIs
Publication statusPublished - 2003 Mar 27

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Porphyrins
Dihedral angle
porphyrins
Dimers
dihedral angle
Fluorescence
dimers
fluorescence
straps
energy
Absorption spectra
excitation
Infrared radiation
absorption spectra
life (durability)
Infrared absorption
Excited states
infrared absorption
time constant
Viscosity

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry

Cite this

Cho, Hyun Sun ; Song, Jae Kyu ; Ha, Jeong Hyon ; Cho, Sung ; Kim, Dongho ; Yoshida, Naoya ; Osuka, Atsuhiro. / Comparative studies on energy relaxation dynamics of directly linked ZnII porphyrin dimers with different dihedral angles. In: Journal of Physical Chemistry A. 2003 ; Vol. 107, No. 12. pp. 1897-1903.
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Comparative studies on energy relaxation dynamics of directly linked ZnII porphyrin dimers with different dihedral angles. / Cho, Hyun Sun; Song, Jae Kyu; Ha, Jeong Hyon; Cho, Sung; Kim, Dongho; Yoshida, Naoya; Osuka, Atsuhiro.

In: Journal of Physical Chemistry A, Vol. 107, No. 12, 27.03.2003, p. 1897-1903.

Research output: Contribution to journalArticle

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AU - Cho, Hyun Sun

AU - Song, Jae Kyu

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AU - Kim, Dongho

AU - Yoshida, Naoya

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AB - Photophysical properties of the strapped ZnII porphyrin dimers (Sn, the strap chain between the porphyrins changes; -O-(CH2)n-O-, n = 1, 2, 3, 4, 8, and 10) and directly linked ZnII porphyrin dimer (Z2) have been investigated by the steady-state and time-resolved spectroscopic methods. The reduced dihedral angle in Sn gives rise to additional absorption bands around 400 nm as well as broad fluorescence in the near-infrared region. The fluorescence lifetimes of Sn become gradually, but not so significantly, shorter as the strap length becomes shorter, indicating that the lifetimes of the lowest excited singlet states of Sn are not affected much despite their structural distortions such as mean plane deviations and the existence of two conformers. Fluorescence excitation and viscosity-dependent fluorescence spectra suggest that S2 exists as two conformers. A and B conformer, which has been also confirmed by X-ray data. The B conformer with a shorter interporphyrin distance has stronger interporphyrin interactions than the A conformer, which was revealed by the fluorescence excitation and fluorescence spectra. The A conformer is responsible for the shorter wavelength fluorescence at ca. 660 nm, whereas the B conformer gives rise to the near-infrared fluorescence. The photoinduced near-infrared absorption band was suggested to be characteristic of S2, which was not observed in Z2. The conformational dynamics of S2 with a time constant of 15 ps was observed in the transient absorption and fluorescence upconversion measurements. From the comparative studies of Z2 and Sn, we have demonstrated that the orientation of the two porphyrin macrocycles has a considerable effect on their photophysical properties.

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