Ferrocenyl helquats: Unusual chiral organometallic nonlinear optical chromophores

Research output: Contribution to journalArticle

  • External authors:
  • Laura E R Buckley
  • Daniela Rusanova-Naydenova
  • Sergio Sánchez
  • Michael Jirásek
  • Vishwas D. Joshi
  • Jan Vávra
  • Dushant Khobragade
  • Lubomír Pospíšil
  • Šárka Ramešová
  • Ivana Císařová
  • David Šaman
  • Radek Pohl
  • Koen Clays
  • Nick Van Steerteghem
  • Bruce S. Brunschwig
  • Filip Teplý

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+/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 PF6 - salt, revealing a centrosymmetric packing in the triclinic space group P1. 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.

Bibliographical metadata

Original languageEnglish
Pages (from-to)1052-1064
Number of pages13
JournalDalton Transactions
Volume46
Issue number4
Early online date20 Dec 2016
DOIs
StatePublished - 2017