Electron- and X-ray Spectroscopy on Novel and Classical Charge Transfer Complexes

K. Medjanik, S.A. Nepijko, D. Kutnyakhov and G. Schönhense

Organic charge-transfer (CT) compounds are a class of materials that exhibit a variety of competing interactions between the charge, spin and lattice degrees of freedom, leading to a wide range of interesting physical properties. Metallic conductivity, superconductivity and magnetism result from the high degree of electronic correlation. This thesis focuses on the electronic structure of CT-compounds from three families of materials by applying various photoemission and X-ray techniques. New molecules with tuneable donor and acceptor strength (tailored via functional end groups), synthesized in the MPI für Polymerforschung, serve as building blocks in new CT complexes.

The studied molecules derive from the parent molecules coronene (donor hexamethoxycoronene HMC;acceptor coronene-hexaone COHON, see figure) and pyrene (donors tetra- and hexamethoxypyrene TMP and HMP) in complex with the classical strong acceptor tetracyanoquinodimethane TCNQ. Molecular orbital and binding energy calculations (from the PhD Thesis of S. Naghavi, Inst. for Inorganic and Analytical Chemistry) serve as guideline for the assignment of peaks in UPS spectra and level positions and level shifts upon formation of the CT complex. Examples of calculated orbitals are shown in Fig. 1. As third family of compounds we studied CT-salts of κ-(BEDT-TTF)2X type, which are located close to a bandwidth-controlled Mott transition in the phase diagram. These samples were synthesized at Goethe-University Frankfurt.

Part of the experiments are complemented by Scanning Tunnelling Spectroscopy (STS) measurements in the group of H. J. Elmers.

 

Figure 1: Structures of the coronene-derivatives and the parent molecule (centre), charge density plots and orbital plots of the highest occupied molecular orbitals.

 

References:

Electronic Structure of Large Disc-Type Donors and Acceptors. K. Medjanik, D. Kutnyakhov, S. A. Nepijko, G. Schönhense, S. Naghavi, V. Alijani, C. Felser, N. Koch, R. Rieger, M. Baumgarten, and K. Müllen, Pys. Chem. Chem. Phys. 12 (2011) 7184-7193

Formation of an Intermolecular Charge-Transfer Compound in UHV Co-Deposited Tetramethoxypyrene and Tetracyanoquinodimethan.K. Medjanik, S. Perkert, S. Naghavi, M. Rudloff, V. Solovyeva, D. Chercka, M. Huth, S. A. Nepijko, T. Methfessel, C. Felser, M. Baumgarten, K. Müllen, H.J. Elmers and G. Schönhense, Phys. Rev. B 82 (2010) 245419

Theoretical Study of Acceptors and Donors Based on Polycyclic Aromatic Molecules. S. Naghavi, T. Gruhn, V. Alijani, G. H. Fecher, C. Felser, K. Medjanik, D. Kutnyakhov, S. A. Nepijko, G. Schönhense, R. Rieger, M. Baumgarten, and K. Müllen, J. Mol. Spec. (2011), in print; and Cond-mat arXiv 1012.3028

Orbital-Resolved Partial Charge Transfer from the Methoxy Groups of Substituted Pyrenes in Complexes with Tetracyanoquinodimethane - a NEXAFS Study. K. Medjanik, S. A. Nepijko, H. J. Elmers and G. Schönhense, P. Nagel, M. Merz, S. Schuppler, D.Chercka, M. Baumgarten, and K. Müllen, Cond-mat arXiv 1012.3467

Study of Charge Transfer Complexes Containing Functionalized p-Conjugated Molecules Using Hard X-ray Photoemission. K. Medjanik, A. Gloskovskii, S. Thiess, H. Schulz-Ritter, W. Drube, D. Chercka, M. Baumgarten, K. Müllen, C. Felser, and G. Schönhense, in preparation

Giant Chemical Shifts of the Sulphur 2s-Line Close to the Glass-Like Transition of the CT Salt k-(BEDT-TTF)2Cu[N(CN)2]Br - a Hard X-ray Photoemission Study. G. Schönhense, M. de Souza, K. Medjanik, A. Gloskovski, H.J. Elmers, J. Müller, and M. Lang, in preparation

Acknowledgements:

The project is funded through Transregio SFB TR 49 (Frankfurt, Mainz, Kaiserslautern), the Graduate School of Excellence MAINZ and Centre for Complex Materials (COMATT), Mainz.

 

 

 

Last update: Friday, 04-Nov-2011 12:34:53 CET Email D. Panzer Impressum