Charge-transfer state and large first hyperpolarizability constant in a highly electronically coupled zinc and gold porphyrin dyad

Jérôme Fortage, Annabelle Scarpaci, Lydie Viau, Yann Pellegrin, Errol Blart, Magnus Falkenström, Leif Hammarström, Inge Asselberghs, Ruben Kellens, Wim Libaers, Koen Clays, Mattias P. Eng, Fabrice Odobel

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Abstract

We report the synthesis and the characterizations of a novel dyad composed of a zinc porphyrin (ZnP) linked to a gold porphyrin (AuP) through an ethynyl spacer. The UV/Vis absorption spectrum and the electrochemical properties clearly reveal that this dyad exhibits a strong electronic coupling in the ground state as evidenced by shifted redox potentials and the appearance of an intense chargetransfer band localized at X = 739 nm in dichloromethane. A spectroelectrochemical study of the dyad along with the parent homometallic system (i.e., ZnP-ZnP and AuP-AuP) was under-taken to determine the spectra of the reduced and oxidized porphyrin units. Femtosecond transient absorption spectroscopic analysis showed that the photoexcitation of the heterometallic dyad leads to an ultrafast formation of a charge-separated state ( +ZnP-AuṖ) that displays a particularly long lifetime (τ = 4ns in toluene) for such a short separation distance. The molecular orbitais of the dyad were determined by DFT quantum-chemical calculations. This theoretical study confirms that the observed intense band at λ = 739nm corresponds to an interporphyrin charge-transfer transition from the HOMO orbital localized on the zinc porphyrin to LUMO orbitais localized on the gold porphyrin. Finally, a Hyper-Rayleigh scattering study shows that the dyad possesses a large first molecular hyperpolarizability coefficient (β = 2100 × 10 -30 esu at λ = 1064 nm), thus highlighting the valuable nonlinear optical properties of this new type of push-pull porphyrin system.

Original languageEnglish
Pages (from-to)9058-9067
Number of pages10
JournalChemistry - A European Journal
Volume15
Issue number36
DOIs
Publication statusPublished - Sep 14 2009

Keywords

  • Charge transfer fluorescence
  • Nonlinear optics
  • Photochemistry
  • Porphyrinoids

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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    Fortage, J., Scarpaci, A., Viau, L., Pellegrin, Y., Blart, E., Falkenström, M., Hammarström, L., Asselberghs, I., Kellens, R., Libaers, W., Clays, K., Eng, M. P., & Odobel, F. (2009). Charge-transfer state and large first hyperpolarizability constant in a highly electronically coupled zinc and gold porphyrin dyad. Chemistry - A European Journal, 15(36), 9058-9067. https://doi.org/10.1002/chem.200900262