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

Abstract

The syntheses of [1,3,5-{(η 2 -dppe)(η 5 -C 5 Me 5 )FeCtC-4-C 6 H 4 CtC} 3 C 6 H 3 ] (1) and [(η 2 -dppe)-(η 5 -C 5 Me 5 )Fe(CtC-1,4-C 6 H 4 CtCPh)] (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-{(η 2 -dppe)(η 5 -C 5 Me 5 )FeCtC} 3 C 6 H 3 ] (3) and [(η 2 -dppe)(η 5 -C 5 Me 5 )FeCtCPh] (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.

Electron‐Rich Iron/Ruthenium Arylalkynyl Complexes for Third‐Order Nonlinear Optics: Redox‐Switching between Three States

“…[14] These alkyne bonds give rise to two diagnostic 13 C NMR signals at 94.4 and 90.0 ppm, absent in the spectrum of 3-H. A TEM image reveals molecules of 4 deposited on an alumina support with a diameter of around 55 , consistent with that suggested by molecular modeling (see the Experimental Section (Computational Details) and the Supporting Information).…”

“…Although the magnitude of the TPA for a given compound originates in part from the match between twice the incoming beam energy and the energy of the TPA excited state, the data are suggestive of significantly higher TPA cross-sections for 3-NO 2 and 4, as previously seen with nitrophenylethynyl complexes or complexes of octupolar symmetry such as 1 a or 1 b. [14,15] Upon mono-oxidation, an increase in the magnitude of g imag and of the TPA cross-section s 2 for the linear complexes is seen. The second oxidation switches the behavior of these compounds from two-photon absorbers to saturable absorbers (the latter corresponding to negative g imag values).…”

“…[6c, 14] Comparison with cubic NLO data previously obtained for the mononuclear compound 11 (Scheme 11; s 2 = 66 AE 15 GM with the incident beam at 695 nm) reveals that 2 behaves as a slightly less efficient twophoton absorber, which indicates that the presence of a second metal center in a given carbon-rich manifold does not always translate into an improvement in its cubic NLO response. [35] However, the primary interest in developing such heterobinuclear complexes resides in the enhanced redox switchability of these systems (for which three states are accessible) compared with their mononuclear counterparts.…”

“…Negative refractive cubic hyperpolarizabilities have also been previously found for mono-or polynuclear Ru II /Ru III or Fe II / Fe III complexes, such as 1 a, 1 b (Scheme 1) or 7-H or 8-H (Scheme 6), and are likely to result from two-photon dispersion effects. [14,15,33] Imaginary parts of the cubic hyperpolarizabilities (g imag ) are also dependent on the energy of the incoming laser beam and reflect the efficiency of nonlinear absorption by the sample at that wavelength. At 750 nm, positive g imag values were found with the neutral molecules, which implies two-photon absorption (TPA) processes.…”

Polynuclear carbon-rich organometallic complexes: clarification of the role of the bridging ligand in the redox properties

“…38a, 80 It has also been shown that modified electron-rich dinuclear acetylide complexes 31 can be grafted onto hydrogenated silicon surfaces and exhibit facile stepwise electron transfer between the bound metal centres and the silicon surface through the interfacial Si-C bond, paving the way to devices.…”