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Published May 17, 2013 | Supplemental Material
Journal Article Open

Heptametallic, Octupolar Nonlinear Optical Chromophores with Six Ferrocenyl Substituents

Abstract

New complexes with six ferrocenyl (Fc) groups connected to ZnII or Cd^(II) tris(2,2′-bipyridyl) cores are described. A thorough characterisation of their BPh_(4)− salts includes two single-crystal X-ray structures, highly unusual for such species with multiple, extended substituents. Intense, visible d(Fe^(II))→π* metal-to-ligand charge-transfer (MLCT) bands accompany the π→π* intraligand charge-transfer absorptions in the near UV region. Each complex shows a single, fully reversible Fe^(III/II) wave when probed electrochemically. Molecular quadratic nonlinear optical (NLO) responses are determined by using hyper-Rayleigh scattering and Stark spectroscopy. The latter gives static first hyperpolarisabilities β_0 reaching as high as approximately 10^(−27) esu and generally increasing with π-conjugation extension. Z-scan cubic NLO measurements reveal high two-photon absorption cross-sections σ2 of up to 5400 GM in one case. DFT calculations reproduce the π-conjugation dependence of β_0, and TD-DFT predicts three transitions close in energy contributing to the MLCT bands. The lowest energy transition has octupolar character, whereas the other two are degenerate and dipolar in nature.

Additional Information

© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Received: December 13, 2012; Published online: March 27, 2013. We thank the EPSRC for support (grants EP/D070732 and EP/G02099) and also the Fund for Scientific Research-Flanders (FWO-V, G.0312.08), the University of Leuven (GOA/2011/03), The Foundation for Polish Science (Welcome grant to M.S.), MCyT-FEDER (CTQ2005–01368, CTQ2008–02942) and Gobierno de Aragon-Fondo Social Europeo (E39). B.S.B. acknowledges the Beckman Institute of the California Institute of Technology for support. We are grateful to Dr John E. Warren (Synchrotron Radiation Source, CCLRC, Daresbury Laboratory, Warrington, WA4 4AD, U.K.) for help with the data collection for the crystal structure determination of 1·6MeNO_2. We also thank Dr John Fielden (Manchester) and Dr Inge Asselberghs (Leuven) for carrying out preliminary HRS measurements, and Nick Van Steerteghem (Leuven) for assistance with these experiments. D.R. thanks Prof Robert Dryfe (Manchester) for helpful discussions about electrochemistry.

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August 22, 2023
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