Third-order nonlinear optical properties of some electron-rich iron mono- And trinuclear alkynyl complexes

The syntheses of [1,3,5-{(n²-dppe)(n⁵-C ₅Me₅)FeC≡C-4-C₆H₄C} ₃C₆H₃] (1) and [(n²-dppe)(n ⁵-C₅Me₅)Fe(C≡C-1,4-C₆H ₄C=CPh)] (2) are reported, together with an X-ray diffraction study of 2. The linear optical spectra of these compounds reveal characteristic low-energy transitions at 430 and 436 nm, respectively, significantly red shifted in comparison to those recorded for [1,3,5-{(n²-dppe)(n ⁵-C₅Me₅)FeC=C}₃C₆H ₃] (3) and [(n²-dppe)(n⁵-C₅Me ₅)FeC≡CPh] (4), respectively. Cubic nonlinear optical response 'data for 1, 2, and 4 are reported. Cubic molecular nonlinearities by Z-scan at 695 nm reveal an increase in nonlinearities upon introduction of the ligated metal unit and progression from linear monometallic complex to octupolar trimetallic complex. Oxidation of 1 to 1³⁺ results in a change of sign and magnitude of the imaginary (absorptive) part of the third-order nonlinearity; that is, the molecule can be electrochemically cycled between two-photon absorber and saturable absorber states.