title: Ferrocenyl helquats: unusual chiral organometallic nonlinear optical chromophores.
abstract: 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+/0redox 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 PF6-salt, revealing a centrosymmetric packing in the triclinic space group P1[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 βtotvalue to decrease by more than 80% in one of the complexes.
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. b.coe@manchester.ac.uk.
authors.forename: Laura E R
authors.initials: LE
authors.lastname: Buckley
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. b.coe@manchester.ac.uk.
authors.forename: Benjamin J
authors.identifier: http://orcid.org/0000-0002-5998-3895
authors.initials: BJ
authors.lastname: Coe
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. b.coe@manchester.ac.uk.
authors.forename: Daniela
authors.initials: D
authors.lastname: Rusanova
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. b.coe@manchester.ac.uk.
authors.forename: Sergio
authors.initials: S
authors.lastname: Sánchez
authors.affiliation: The Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo n. 542/2, 166 10 Prague 6, Czech Republic. filip.teply@uochb.cas.cz.
authors.forename: Michael
authors.initials: M
authors.lastname: Jirásek
authors.affiliation: The Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo n. 542/2, 166 10 Prague 6, Czech Republic. filip.teply@uochb.cas.cz.
authors.forename: Vishwas D
authors.initials: VD
authors.lastname: Joshi
authors.affiliation: The Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo n. 542/2, 166 10 Prague 6, Czech Republic. filip.teply@uochb.cas.cz.
authors.forename: Jan
authors.initials: J
authors.lastname: Vávra
authors.affiliation: The Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo n. 542/2, 166 10 Prague 6, Czech Republic. filip.teply@uochb.cas.cz.
authors.forename: Dushant
authors.initials: D
authors.lastname: Khobragade
authors.affiliation: J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, 18223 Prague 8, Czech Republic.
authors.forename: Lubomír
authors.initials: L
authors.lastname: Pospíšil
authors.affiliation: J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences, 18223 Prague 8, Czech Republic.
authors.forename: Šárka
authors.initials: Š
authors.lastname: Ramešová
authors.affiliation: Department of Inorganic Chemistry, Charles University, Hlavova 2030/8, 128 43 Prague 2, Czech Republic.
authors.forename: Ivana
authors.initials: I
authors.lastname: Císařová
authors.affiliation: The Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo n. 542/2, 166 10 Prague 6, Czech Republic. filip.teply@uochb.cas.cz.
authors.forename: David
authors.initials: D
authors.lastname: Šaman
authors.affiliation: The Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo n. 542/2, 166 10 Prague 6, Czech Republic. filip.teply@uochb.cas.cz.
authors.forename: Radek
authors.initials: R
authors.lastname: Pohl
authors.affiliation: Department of Chemistry, University of Leuven, Celestijnenlaan 200 D, B-3001, Belgium.
authors.forename: Koen
authors.initials: K
authors.lastname: Clays
authors.affiliation: Department of Chemistry, University of Leuven, Celestijnenlaan 200 D, B-3001, Belgium.
authors.forename: Nick
authors.initials: N
authors.lastname: Van Steerteghem
authors.affiliation: Molecular Materials Research Center, Beckman Institute, MC 139-74, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA.
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Brunschwig
authors.affiliation: The Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo n. 542/2, 166 10 Prague 6, Czech Republic. filip.teply@uochb.cas.cz.
authors.forename: Filip
authors.initials: F
authors.lastname: Teplý