Orbital-resolved partial charge transfer from the methoxy groups of substituted pyrenes in complexes with tetracyanoquinodimethane - A NEXAFS study

Katerina Medjanik, Dennis Chercka, Peter Nagel, Michael Merz, Stefan Schuppler, Martin Baumgarten, Klaus Müllen, Sergej A. Nepijko, Hans Joachim Elmers, Gerd Schönhense, Harald Olaf Jeschke, Roser Valenti

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17 Citations (Scopus)

Abstract

It is demonstrated that the near-edge X-ray absorption fine structure (NEXAFS) provides a powerful local probe of functional groups in novel charge transfer (CT) compounds and their electronic properties. Microcrystals of tetra-/hexamethoxypyrene as donors with the strong acceptor tetracyano-p- quinodimethane (TMP/HMP-TCNQ) were grown by vapor diffusion. The oxygen and nitrogen K-edge spectra are spectroscopic fingerprints of the functional groups in the donor and acceptor moieties, respectively. The orbital selectivity of the NEXAFS pre-edge resonances allows us to precisely elucidate the participation of specific orbitals in the charge transfer process. Upon complex formation, the intensities of several resonances change substantially and a new resonance occurs in the oxygen K-edge spectrum. This gives evidence of a corresponding change of hybridization of specific orbitals in the functional groups of the donor (those derived from the frontier orbitals 2e and 6a 1 of the isolated methoxy group) and acceptor (orbitals b 3g, a u, b 1g, and b 2u, all located at the cyano group) with π*-orbitals of the ring systems. Along with this intensity effect, the resonance positions associated with the oxygen K-edge (donor) and nitrogen K-edge (acceptor) shift to higher and lower photon energies in the complex, respectively. A calculation based on density functional theory qualitatively explains the experimental results. NEXAFS measurements shine light on the action of the functional groups and elucidate charge transfer on a submolecular level.

Original languageEnglish
Pages (from-to)4694-4699
Number of pages6
JournalJournal of the American Chemical Society
Volume134
Issue number10
DOIs
Publication statusPublished - Mar 14 2012
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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    Medjanik, K., Chercka, D., Nagel, P., Merz, M., Schuppler, S., Baumgarten, M., Müllen, K., Nepijko, S. A., Elmers, H. J., Schönhense, G., Jeschke, H. O., & Valenti, R. (2012). Orbital-resolved partial charge transfer from the methoxy groups of substituted pyrenes in complexes with tetracyanoquinodimethane - A NEXAFS study. Journal of the American Chemical Society, 134(10), 4694-4699. https://doi.org/10.1021/ja2100802