An extremely long-lived charge-separated state of zinc tetraphenylporphyrin coordinated with pyridylnaphthalene-diimide

Kenji Saito, Yukiyasu Kashiwagi, Kei Ohkubo, Shunichi Fukuzumi

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The nitrogen of pyridylnaphthalenediimide (PyNIm) coordinates to the metal center of zinc tetraphenylporphyrin (ZnTPP) to form a donor-acceptor complex: ZnTPP-PyNIm. Formation of the ZnTPP-PyNIm complex was probed by UV-vis, fluorescence and NMR spectra. The fluorescence of ZnTPP is strongly quenched and the fluorescence lifetime is shortened significantly in the complex. The transient absorption spectrum of the charge-separated state (ZnTPP •+-PyNIm•-) is successfully detected by laser flash photolysis measurements of the ZnTPP-PyNIm system in benzonitrile. The charge-separated state of the complex produced by the photoinduced electron transfer has the longest lifetime, (450 μs) at 288 K, ever reported for donor-acceptor systems linked covalently or non-covalently in solution. However, when benzonitrile is replaced by benzene, the triplet excited state ( 3ZnTPP*), rather than the charge-separated state, is formed upon laser excitation of the ZnTPP-PyNIm complex, due to the lower energy of 3ZnTPP* compared to the charge-separated state in benzene.

Original languageEnglish
Pages (from-to)1371-1379
Number of pages9
JournalJournal of Porphyrins and Phthalocyanines
Issue number12
StatePublished - 2006

Bibliographical note

Funding Information:
This work was supported by a Grant-in-Aid (No. 17750039) from the Ministry of Education, Culture, Sports, Science and Technology, Japan. We thank Dr. Yasuyuki Araki and Prof. Osamu Ito for fluorescence lifetime measurements. K. S. and Y. K. express their special thanks for the center of excellence (21COE) program “Creation of Integrated EcoChemistry of Osaka University”.


  • Charge separation
  • Donor-acceptor complex
  • Photoinduced electron transfer
  • Zinc porphyrin


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