International audienceStudies of the nonlinear optical (NLO) properties of Group 8 metal alkynyl complexes are summarized, with particular focus on results since 2003; structure-NLO property relationships are developed, optical nonlinearities of multipolar alkynyl complexes are described, and switching of the NLO response of molecules and molecular materials derived from Group 8 metal alkynyl complexes is discussed

International audienceThe 2,7-fluorenyl-bridged Fe(?5-C5Me5)(?2-dppe)[C≡C(2,7-C13H6Bu2)C≡C]Fe(?5-C5Me5)(?2-dppe) (1a), its extended analogue Fe(?5-C5Me5)(?2-dppe)[C≡C(1,4-C6H4)C≡C(2,7-C13H6Bu2)C≡C(1,4-C6H4)C≡C](?5-C5Me5)(?2-dppe)Fe (1b), and the corresponding mononuclear complexes Fe(?5-C5Me5)(?2-dppe)[C≡C(2-C13H7Bu2)] (2a) and Fe(?5-C5Me5)(?2-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 performanc