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Ferrocenyl helquats: unusual chiral organometallic nonlinear optical chromophores

Buckley, Laura E. R. and Coe, Benjamin J. and Rusanova, Daniela and Sánchez, Sergio and Jirásek, Michael and Joshi, Vishwas D. and Vávra, Jan and Khobragade, Dushant and Pospíšil, Lubomír and Ramešová, Šárka and Císařová, Ivana and Šaman, David and Pohl, Radek and Clays, Koen and Van Steerteghem, Nick and Brunschwig, Bruce S. and Teplý, Filip (2017) Ferrocenyl helquats: unusual chiral organometallic nonlinear optical chromophores. Dalton Transactions, 46 (4). pp. 1052-1064. ISSN 1477-9226. doi:10.1039/C6DT04347J.

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Three new dipolar cations have been synthesised, containing ferrocenyl (Fc) electron donor groups attached to helquat (Hq) acceptors. These organometallic Hq derivatives have been characterised as their TfO^− salts by using various techniques including NMR and electronic absorption spectroscopies and electrochemical measurements. UV–vis spectra show multiple intense low energy absorptions attributable to intramolecular charge-transfer (ICT) excitations. Each compound displays a reversible Fc^(+/0) redox process, together with two reversible one-electron reductions of the Hq fragment. Molecular quadratic nonlinear optical (NLO) responses have been determined by using hyper-Rayleigh scattering at 1064 nm, and Stark (electroabsorption) spectroscopic studies on the visible absorption bands. The obtained first hyperpolarizabilities β are moderate, consistent with the relatively short π-conjugation lengths between the Fc and attached pyridinium group. A single-crystal X-ray structure has been solved for one of the complexes as its PF_6^− salt, revealing a centrosymmetric packing in the triclinic space group P[1 with combining macron]. Density functional theory (DFT) and time-dependent DFT calculations indicate that the lowest energy absorption bands have mainly metal-to-ligand charge-transfer character. The donor orbitals involved in the electronic transitions forming the next lowest energy ICT band also have substantial contributions from the Fe atom. Good agreement between the simulated and experimental UV–vis absorption spectra is achieved by using the PBE0 functional with the 6-311++G(d)/LANL2DZ mixed basis set, and the theoretical β values are reasonably large. Oxidation of the Fc unit is predicted to cause the βtot value to decrease by more than 80% in one of the complexes.

Item Type:Article
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URLURL TypeDescription
Coe, Benjamin J.0000-0002-5998-3895
Brunschwig, Bruce S.0000-0002-6135-6727
Additional Information:© 2016 Royal Society of Chemistry. Received 16th November 2016, Accepted 19th December 2016. First published on the web 20th December 2016. We thank the following for financial support: the EPSRC (grant EP/J018635/1), the ASCR (RVO: 61388963, M200551208 to F. T.), the Czech Science Foundation (grant 13-19213S to F. T. and 16-030855 to L. P.), the Hercules Foundation, the Fund for Scientific Research-Flanders (Research Grant 1510712N and a PhD Fellowship to N. V. S.) and the University of Leuven (GOA/2011/03). B. S. B. thanks the Beckman Institute of the California Institute of Technology for support.
Funding AgencyGrant Number
Engineering and Physical Sciences Research Council (EPSRC)EP/J018635/1
Academy of Sciences of the Czech Republic61388963
Academy of Sciences of the Czech RepublicM200551208
Czech Science Foundation13-19213S
Czech Science Foundation16-030855
Hercules FoundationUNSPECIFIED
Fonds Wetenschappelijk Onderzoek - Vlaanderen (FWO)1510712N
University of LeuvenGOA/2011/03
Caltech Beckman InstituteUNSPECIFIED
Issue or Number:4
Record Number:CaltechAUTHORS:20170104-165010873
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73249
Deposited By: George Porter
Deposited On:05 Jan 2017 16:33
Last Modified:11 Nov 2021 05:13

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