title: Heptametallic, octupolar nonlinear optical chromophores with six ferrocenyl substituents.
abstract: New complexes with six ferrocenyl (Fc) groups connected to Zn(II) or Cd(II) tris(2,2'-bipyridyl) cores are described. A thorough characterisation of their BPh4(-) 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 β0 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 β0, 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.
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. b.coe@manchester.ac.uk
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Coe
authors.forename: Simon P
authors.initials: SP
authors.lastname: Foxon
authors.forename: Madeleine
authors.initials: M
authors.lastname: Helliwell
authors.forename: Daniela
authors.initials: D
authors.lastname: Rusanova
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Brunschwig
authors.forename: Koen
authors.initials: K
authors.lastname: Clays
authors.forename: Griet
authors.initials: G
authors.lastname: Depotter
authors.forename: Marcin
authors.initials: M
authors.lastname: Nyk
authors.forename: Marek
authors.initials: M
authors.lastname: Samoc
authors.forename: Dominika
authors.initials: D
authors.lastname: Wawrzynczyk
authors.forename: Javier
authors.initials: J
authors.lastname: Garín
authors.forename: Jesús
authors.initials: J
authors.lastname: Orduna
mesh_terms: D015082:2,2'-Dipyridyl / Q000737:chemistry*; D002104:Cadmium / Q000737:chemistry; D002863:Chromogenic Compounds / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005296:Ferrous Compounds / Q000737:chemistry*; D008024:Ligands; D008956:Models, Chemical; D010084:Oxidation-Reduction; D012492:Salts / Q000737:chemistry; D013057:Spectrum Analysis; D015032:Zinc / Q000737:chemistry
chemical_list: D002863:Chromogenic Compounds; D056831:Coordination Complexes; D005296:Ferrous Compounds; D008024:Ligands; D012492:Salts; D002104:Cadmium; D015082:2,2'-Dipyridyl; D015032:Zinc