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

The syntheses of [1,3,5-{eta(2)-dppe)(eta(5)-C5Me5)FeC C-4-C6H4C C}(3)C6H3] (1) and [(eta(2)-dppe)- (eta(5)-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 [1,3,5-1(eta(5)-dppe)(eta(5)-C5Me5)FeC C}(3)C6H3] (3) and [(eta(2)-dppe)(eta(5)-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.