Dresden 2011 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 100: Organic electronics and photovoltaics

O 100.3: Vortrag

Freitag, 18. März 2011, 11:45–12:00, WIL B122

Elucidation of Partial Charge Transfer from the Methoxy Groups of Substituted Pyrene as Donor in Complexes with Tetracyanoquinodimethane — •Katerina Medjanik¹, Sergej Nepijko¹, Hans-Joachim Elmers¹, Gerd Schönhense¹, Peter Nagel², Stefan Schuppler², Dennis Chercka³, Martin Baumgarten³, and Klaus Müllen³ — ¹Ins. für Physik, Johannes Gutenberg-Universität,Mainz — ²Karlsruhe Institute of Technology, ANKA — ³Max-Planck Ins. for Polymer Research, Mainz

Novel charge transfer (CT) compounds can be synthesized on the basis of large polycyclic aromatic hydrocarbons [1]. Microcrystals of the CT-compounds tetra- and hexamethoxypyrene/tetracyanoquinodimethane (TMP_x/HMP_x-TCNQ_y) in different stoichiometries x:y=1:1, 1:2 and 2:1 were grown from solution via vapour diffusion. These crystallite fractions were studied by NEXAFS with particular emphasis on direct fingerprints of a charge transfer. Oxygen and nitrogen K-edge NEXAFS gives direct access to the unoccupied orbitals in the donor and acceptor, respectively. With increasing HMP content, a strongly rising O 1s pre-edge signal comes along with a substantial drop of N 1s resonance intensity. Charge is transferred from the π^*-orbital of the methoxy-group to the σ^*-orbitals b_1g and b_2u and - to a weaker extent - to the π^*-orbitals b_3g and a_u of the cyano-group of TCNQ, particularly strong for the 2:1 compound. Funded by DFG/TR49, Graduate School of Excellence MAINZ, Centre of Complex Materials COMATT.

[1] K. Medjanik et al., Phys. Chem. Chem. Phys. 12, 7184 (2010)