Third-Order Nonlinear Optical Properties of Some Electron-Rich Iron Mono- and Trinuclear Alkynyl Complexes

The syntheses of [1,3,5-{(η2-dppe)(η5-C5Me5)FeC⋮C-4-C6H4C⋮C}3C6H3] (1) and [(η2-dppe)(η5-C5Me5)Fe(C⋮C-1,4-C6H4C⋮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-{(η2-dppe)(η5-C5Me5)FeC⋮C}3C6H3] (3) and [(η2-dppe)(η5-C5Me5)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 1 3+ 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.