Linkage dependent charge separation and charge recombination in porphyrin-pyromellitimide-fullerene triads

Hiroshi Imahori, Koichi Tamaki, Yasuyuki Araki, Taku Hasobe, Osamu Ito, Akihisa Shimomura, Santi Kundu, Tadashi Okada, Yoshiteru Sakata, Shunichi Fukuzumi

Research output: Contribution to journalArticle

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Abstract

A homologous series of zincporphyrin (ZnP)-pyromellitimide (Im)-C60 linked triads where the pyromellitimide (Im) moiety is incorporated as an intermediate acceptor between the above two chromophores with a linkage of different spacers, ZnP-Im-CH2-C60, ZnP-Im-C60, and ZnP-CH2-Im-C60 as well as the reference dyads (ZnP-Im-CH2-ref, ZnP-Im-ref, and ZnP-CH2-Im-ref) have been prepared to investigate linkage dependence of photoinduced electron transfer (ET) and back ET to the ground state in the triads. Time-resolved transient absorption spectra of the triads measured by picosecond laser photolysis as well as the fluorescence lifetimes in THF reveal the occurrence of photoinduced ET from the singlet excited state of the ZnP to the Im moiety to give the initial charge-separated state, i.e., the zincporphyrin radical cation (ZnP.+)-imide radical anion (Im.-) pair, followed by a charge shift (CSH) to produce the final charge-separated state, the ZnP.+-C60.- pair. The rate constants of photoinduced ETs in ZnP-Im-C60 (1.8 × 1010 s-1) and ZnP-Im-CH2-C60 (1.3 × 1010 s-1) in THF are much larger than those in ZnP-CH2-Im-C60 (2.9 × 109 s-1) and ZnP-CH2-Im-ref (1.9 × 109 s-1). The larger charge separation (CS) rates in the former case are ascribed to the relatively strong electronic coupling because of the absence of a methylene linkage between the ZnP and the Im moieties in ZnP-Im-C60 and ZnP-Im-CH2-C60 as compared to the triad and dyad with the methylene linkage. The transient absorption spectra of the final charge-separated state, the ZnP.+-C60.- pair, have been also measured by nanosecond laser photolysis. It has been found that the rate constants of charge recombination (CR) of ZnP.+-Im-C60.- are temperature independent, but that the CR rate constants of ZnP.+-Im-CH2-C60.- exhibit an Arrhenius-like temperature dependence with an activation energy of 0.13 eV which corresponds to the energy difference between ZnP.+-Im.--CH2-C60 and ZnP.+-Im-CH2-C60.-. This indicates that the relatively strong electronic coupling without methylene linkage in ZnP-Im-C60 results in the preference of the tunneling superexchange ET over the sequential ET in the CR process which requires the thermal activation to reach the higher energy state (i.e., ZnP.+-Im.--C60), whereas the sequential ET predominates in the triads with the methylene linkage.

Original languageEnglish
Pages (from-to)2803-2814
Number of pages12
JournalJournal of Physical Chemistry A
Volume106
Issue number12
DOIs
Publication statusPublished - 2002 Mar 28
Externally publishedYes

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Fullerenes
Porphyrins
polarization (charge separation)
linkages
porphyrins
fullerenes
electron transfer
methylene
Electrons
Rate constants
Photolysis
Absorption spectra
photolysis
Imides
Electron tunneling
Lasers
absorption spectra
Chromophores
Excited states
imides

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Linkage dependent charge separation and charge recombination in porphyrin-pyromellitimide-fullerene triads. / Imahori, Hiroshi; Tamaki, Koichi; Araki, Yasuyuki; Hasobe, Taku; Ito, Osamu; Shimomura, Akihisa; Kundu, Santi; Okada, Tadashi; Sakata, Yoshiteru; Fukuzumi, Shunichi.

In: Journal of Physical Chemistry A, Vol. 106, No. 12, 28.03.2002, p. 2803-2814.

Research output: Contribution to journalArticle

Imahori, H, Tamaki, K, Araki, Y, Hasobe, T, Ito, O, Shimomura, A, Kundu, S, Okada, T, Sakata, Y & Fukuzumi, S 2002, 'Linkage dependent charge separation and charge recombination in porphyrin-pyromellitimide-fullerene triads', Journal of Physical Chemistry A, vol. 106, no. 12, pp. 2803-2814. https://doi.org/10.1021/jp014433f
Imahori, Hiroshi ; Tamaki, Koichi ; Araki, Yasuyuki ; Hasobe, Taku ; Ito, Osamu ; Shimomura, Akihisa ; Kundu, Santi ; Okada, Tadashi ; Sakata, Yoshiteru ; Fukuzumi, Shunichi. / Linkage dependent charge separation and charge recombination in porphyrin-pyromellitimide-fullerene triads. In: Journal of Physical Chemistry A. 2002 ; Vol. 106, No. 12. pp. 2803-2814.
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T1 - Linkage dependent charge separation and charge recombination in porphyrin-pyromellitimide-fullerene triads

AU - Imahori, Hiroshi

AU - Tamaki, Koichi

AU - Araki, Yasuyuki

AU - Hasobe, Taku

AU - Ito, Osamu

AU - Shimomura, Akihisa

AU - Kundu, Santi

AU - Okada, Tadashi

AU - Sakata, Yoshiteru

AU - Fukuzumi, Shunichi

PY - 2002/3/28

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N2 - A homologous series of zincporphyrin (ZnP)-pyromellitimide (Im)-C60 linked triads where the pyromellitimide (Im) moiety is incorporated as an intermediate acceptor between the above two chromophores with a linkage of different spacers, ZnP-Im-CH2-C60, ZnP-Im-C60, and ZnP-CH2-Im-C60 as well as the reference dyads (ZnP-Im-CH2-ref, ZnP-Im-ref, and ZnP-CH2-Im-ref) have been prepared to investigate linkage dependence of photoinduced electron transfer (ET) and back ET to the ground state in the triads. Time-resolved transient absorption spectra of the triads measured by picosecond laser photolysis as well as the fluorescence lifetimes in THF reveal the occurrence of photoinduced ET from the singlet excited state of the ZnP to the Im moiety to give the initial charge-separated state, i.e., the zincporphyrin radical cation (ZnP.+)-imide radical anion (Im.-) pair, followed by a charge shift (CSH) to produce the final charge-separated state, the ZnP.+-C60.- pair. The rate constants of photoinduced ETs in ZnP-Im-C60 (1.8 × 1010 s-1) and ZnP-Im-CH2-C60 (1.3 × 1010 s-1) in THF are much larger than those in ZnP-CH2-Im-C60 (2.9 × 109 s-1) and ZnP-CH2-Im-ref (1.9 × 109 s-1). The larger charge separation (CS) rates in the former case are ascribed to the relatively strong electronic coupling because of the absence of a methylene linkage between the ZnP and the Im moieties in ZnP-Im-C60 and ZnP-Im-CH2-C60 as compared to the triad and dyad with the methylene linkage. The transient absorption spectra of the final charge-separated state, the ZnP.+-C60.- pair, have been also measured by nanosecond laser photolysis. It has been found that the rate constants of charge recombination (CR) of ZnP.+-Im-C60.- are temperature independent, but that the CR rate constants of ZnP.+-Im-CH2-C60.- exhibit an Arrhenius-like temperature dependence with an activation energy of 0.13 eV which corresponds to the energy difference between ZnP.+-Im.--CH2-C60 and ZnP.+-Im-CH2-C60.-. This indicates that the relatively strong electronic coupling without methylene linkage in ZnP-Im-C60 results in the preference of the tunneling superexchange ET over the sequential ET in the CR process which requires the thermal activation to reach the higher energy state (i.e., ZnP.+-Im.--C60), whereas the sequential ET predominates in the triads with the methylene linkage.

AB - A homologous series of zincporphyrin (ZnP)-pyromellitimide (Im)-C60 linked triads where the pyromellitimide (Im) moiety is incorporated as an intermediate acceptor between the above two chromophores with a linkage of different spacers, ZnP-Im-CH2-C60, ZnP-Im-C60, and ZnP-CH2-Im-C60 as well as the reference dyads (ZnP-Im-CH2-ref, ZnP-Im-ref, and ZnP-CH2-Im-ref) have been prepared to investigate linkage dependence of photoinduced electron transfer (ET) and back ET to the ground state in the triads. Time-resolved transient absorption spectra of the triads measured by picosecond laser photolysis as well as the fluorescence lifetimes in THF reveal the occurrence of photoinduced ET from the singlet excited state of the ZnP to the Im moiety to give the initial charge-separated state, i.e., the zincporphyrin radical cation (ZnP.+)-imide radical anion (Im.-) pair, followed by a charge shift (CSH) to produce the final charge-separated state, the ZnP.+-C60.- pair. The rate constants of photoinduced ETs in ZnP-Im-C60 (1.8 × 1010 s-1) and ZnP-Im-CH2-C60 (1.3 × 1010 s-1) in THF are much larger than those in ZnP-CH2-Im-C60 (2.9 × 109 s-1) and ZnP-CH2-Im-ref (1.9 × 109 s-1). The larger charge separation (CS) rates in the former case are ascribed to the relatively strong electronic coupling because of the absence of a methylene linkage between the ZnP and the Im moieties in ZnP-Im-C60 and ZnP-Im-CH2-C60 as compared to the triad and dyad with the methylene linkage. The transient absorption spectra of the final charge-separated state, the ZnP.+-C60.- pair, have been also measured by nanosecond laser photolysis. It has been found that the rate constants of charge recombination (CR) of ZnP.+-Im-C60.- are temperature independent, but that the CR rate constants of ZnP.+-Im-CH2-C60.- exhibit an Arrhenius-like temperature dependence with an activation energy of 0.13 eV which corresponds to the energy difference between ZnP.+-Im.--CH2-C60 and ZnP.+-Im-CH2-C60.-. This indicates that the relatively strong electronic coupling without methylene linkage in ZnP-Im-C60 results in the preference of the tunneling superexchange ET over the sequential ET in the CR process which requires the thermal activation to reach the higher energy state (i.e., ZnP.+-Im.--C60), whereas the sequential ET predominates in the triads with the methylene linkage.

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