2,7-Fluorenediyl-Bridged Complexes Containing Electroactive “Fe(η⁵-C₅Me₅)(κ²-dppe)C≡C–” End Groups: Molecular Wires and Remarkable Nonlinear Electrochromes

Abstract

The 2,7-fluorenyl-bridged Fe(η5-C5Me5)(κ2-dppe)[C≡C(2,7-C13H6Bu2)C≡C]Fe(η5-C5Me5)(κ2-dppe) (1a), its extended analogue Fe(η5-C5Me5)(κ2-dppe)[C≡C(1,4-C6H4)C≡C(2,7-C13H6Bu2)C≡C(1,4-C6H4)C≡C](η5-C5Me5)(κ2-dppe)Fe (1b), and the corresponding mononuclear complexes Fe(η5-C5Me5)(κ2-dppe)[C≡C(2-C13H7Bu2)] (2a) and Fe(η5-C5Me5)(κ2-dppe)[C≡C(1,4-C6H4)C≡C(2-C13H7Bu2)] (2b), which model half of these molecules, have been synthesized and characterized in their various redox states. The molecular wire characteristics of the dinuclear complexes were examined in their mixed-valent states, with progression from 1a[PF6] to 1b[PF6] resulting in a sharp decrease in electronic coupling. The cubic nonlinear optical properties of these species were investigated over the visible and near-IR range, a particular emphasis being placed on their multiphoton absorption properties; the complexes are shown to function as redox-switchable nonlinear chromophores at selected wavelengths, and the more extended derivatives are shown to exhibit the more promising NLO performance.