Structural dependence on excitation energy migration processes in artificial light harvesting cyclic zinc(II) porphyrin arrays

Min Chul Yoon, Sung Cho, Pyosang Kim, Takaaki Hori, Naoki Aratani, Atsuhiro Osuka, Dongho Kim

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

A series of covalently linked cyclic porphyrin arrays CNZ that consist of N/2 of meso-meso directly linked zinc(II) porphyrin dimer subunits Z2 bridged by 1,3-phenylene spacers have been prepared by AgI-promoted oxidative coupling reaction. We have investigated the excitation energy migration processes of CNZ in toluene by using femtosecond transient absorption anisotropy decay measurements by taking 2Z2 composed of two Z2 units linked by 1,3-phenylene as a reference molecule. On the basis of the excitation energy transfer rate determined for 2Z2, we have revealed the excitation energy hopping rates in the cyclic arrays CNZ by using a regular polygon model. The number of excitation energy hopping sites Nflat calculated by using a regular polygon model is close to the observed Nexpt value obtained from the transient absorption anisotropy decays for C12Z-C18Z with circular and well-ordered structures. On the other hand, a large discrepancy between N flat and Nexpt was found for smaller or larger arrays (C10Z, C24Z, and C32Z). In the case of C10Z, m-phenylene linked 2Z2 motif with the interchromophoric angle of 120° is not well suited to make a cyclic pentagonal array C10Z based on planar pentagonal structure. This geometrical factor inevitably causes a structural distortion in C10Z, leading to a discrepancy between Nexpt and Nflat values. On the contrary, the presence of highly distorted conformers such as figure-eight structures reduces the number of effective hopping sites Nexpt in large cyclic arrays C24Z and C32Z. Thus, our study demonstrates that not only the large number of porphyrin chromophores in the cyclic arrays CNZ but the overall rigidity and three-dimensional orientation in molecular architectures is a key factor to be considered in the preparation of artificial light harvesting porphyrin arrays.

Original languageEnglish
Pages (from-to)15074-15082
Number of pages9
JournalJournal of Physical Chemistry B
Volume113
Issue number45
DOIs
Publication statusPublished - 2009 Dec 11

Fingerprint

Excitation energy
Porphyrins
porphyrins
Zinc
zinc
excitation
Anisotropy
polygons
energy
Toluene
Chromophores
Rigidity
Dimers
Energy transfer
anisotropy
planar structures
decay
Molecules
rigidity
spacers

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Materials Chemistry
  • Surfaces, Coatings and Films

Cite this

Yoon, Min Chul ; Cho, Sung ; Kim, Pyosang ; Hori, Takaaki ; Aratani, Naoki ; Osuka, Atsuhiro ; Kim, Dongho. / Structural dependence on excitation energy migration processes in artificial light harvesting cyclic zinc(II) porphyrin arrays. In: Journal of Physical Chemistry B. 2009 ; Vol. 113, No. 45. pp. 15074-15082.
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abstract = "A series of covalently linked cyclic porphyrin arrays CNZ that consist of N/2 of meso-meso directly linked zinc(II) porphyrin dimer subunits Z2 bridged by 1,3-phenylene spacers have been prepared by AgI-promoted oxidative coupling reaction. We have investigated the excitation energy migration processes of CNZ in toluene by using femtosecond transient absorption anisotropy decay measurements by taking 2Z2 composed of two Z2 units linked by 1,3-phenylene as a reference molecule. On the basis of the excitation energy transfer rate determined for 2Z2, we have revealed the excitation energy hopping rates in the cyclic arrays CNZ by using a regular polygon model. The number of excitation energy hopping sites Nflat calculated by using a regular polygon model is close to the observed Nexpt value obtained from the transient absorption anisotropy decays for C12Z-C18Z with circular and well-ordered structures. On the other hand, a large discrepancy between N flat and Nexpt was found for smaller or larger arrays (C10Z, C24Z, and C32Z). In the case of C10Z, m-phenylene linked 2Z2 motif with the interchromophoric angle of 120° is not well suited to make a cyclic pentagonal array C10Z based on planar pentagonal structure. This geometrical factor inevitably causes a structural distortion in C10Z, leading to a discrepancy between Nexpt and Nflat values. On the contrary, the presence of highly distorted conformers such as figure-eight structures reduces the number of effective hopping sites Nexpt in large cyclic arrays C24Z and C32Z. Thus, our study demonstrates that not only the large number of porphyrin chromophores in the cyclic arrays CNZ but the overall rigidity and three-dimensional orientation in molecular architectures is a key factor to be considered in the preparation of artificial light harvesting porphyrin arrays.",
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Structural dependence on excitation energy migration processes in artificial light harvesting cyclic zinc(II) porphyrin arrays. / Yoon, Min Chul; Cho, Sung; Kim, Pyosang; Hori, Takaaki; Aratani, Naoki; Osuka, Atsuhiro; Kim, Dongho.

In: Journal of Physical Chemistry B, Vol. 113, No. 45, 11.12.2009, p. 15074-15082.

Research output: Contribution to journalArticle

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AU - Yoon, Min Chul

AU - Cho, Sung

AU - Kim, Pyosang

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AU - Osuka, Atsuhiro

AU - Kim, Dongho

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