Nonlinear Optical Chromophores with Two Ferrocenyl, Octamethylferrocenyl, or 4-(Diphenylamino)phenyl Groups Attached to Rhenium(I) or Zinc(II) Centers

Abstract

The compounds 4,4′-bis­[(E)-2-R-vinyl]-2,2′-bipyridyl {R = ferrocenyl [(Fcv)2bpy], octamethylferrocenyl [(Me8Fcv)2bpy] or 4-(diphenylamino)­phenyl [(Dapv)2bpy]} are used to prepare eight new complexes with ZnIICl2, ZnII(OAc)2, or fac-ReICl­(CO)3 centers. The recently reported complex fac-ReICl­(CO)3[(Dapv)2bpy] (Inorg. Chem.2013521304) is also studied. Electronic absorption spectra show intense d → π* metal-to-ligand charge-transfer (MLCT) and π → π* intraligand charge-transfer (ILCT) absorption bands, the relative energies of which correlate logically with the molecular structure. Cyclic voltammetry reveals a reversible oxidation wave for the Fc/Me8Fc complexes, accompanied by quasireversible or irreversible ligand-based reductions. The Re complexes also show irreversible ReII/I waves. Single-crystal X-ray structures are reported for (Me8Fcv)2bpy, ZnIICl2[(Me8Fcv)2bpy], ZnII(OAc)2[(Fcv)2bpy]·CHCl3, and fac-ReICl­(CO)3[(Me8Fcv)2bpy]·0.5CHCl3. Molecular first hyperpolarizabilities β are measured in DCM solutions via the hyper-Rayleigh scattering (HRS) technique at 1300 nm. Stark (electroabsorption) spectroscopic studies on only the MLCT bands in frozen butyronitrile allow the indirect estimation of lower limits for the overall static first hyperpolarizabilities β0. Time-dependent density functional theory (TD-DFT) calculations on selected complexes confirm the expected assignments of their low energy absorption bands, with the best results obtained by using the M06 functional and Def2-TZVP/SVP/TZVPP mixed basis set. DFT predicts that the total static first hyperpolarizability βtot increases in the ZnIICl2 series in the order R = Fc < Me8Fc < Dap, consistent with the HRS and Stark data. The computed β values increase substantially on moving from the gas phase to a DCM or MeCN solvent medium, and the essentially 2D nature of the chromophores leads to dominant β xxy tensor components.

Transition metal(II) complexes featuring push-pull dianionic Schiff base ligands: synthesis, crystal structure, electrochemical, and NLO studies

“…The magnitude of the redox potential of the ferrocenyl group has, indeed, been regarded as an important factor in the study of conjugated push-pull chromophores, being related in many cases with the magnitude of the second-order NLO responses [64,65].…”

Thermally stable ferrocene-α-cyanostilbenes as efficient materials for second order nonlinear optical polarizability

“…[16][17][18][19][20] For example, electrochemical or chemical alteration of the oxidation state from +2 to +3 of the metal centre renders Fc a strong donor or acceptor, depending upon the oxidation state. This concept has lent practicability to the electrochemical redox switching [21][22][23][24][25][26][27] of the NLO response of the Fc D-A dyads. Fc generally possess low oxidation potential and is capable of a facile charge transfer (CT) to an acceptor to yield stable aferrocenyl carbocations.…”

Spontaneous Symmetry Breaking Facilitates Metal-to-Ligand Charge Transfer: A Quantitative Two-Photon Absorption Study of Ferrocene-phenyleneethynylene Oligomers

“…Ferrocene-based complexes possess intriguing nonlinear optical and charge-transport properties, which make them subject to continuing research. − A prominent feature of the UV–vis absorption spectrum of the numerous organometallic complexes of ferrocene (Fc) consists of a broad red-shifted band (or bands) associated with metal-to-ligand charge-transfer (MLCT) transitions, − where a notable fraction of the electron density shifts from the Fe atom(s) in the ground electronic state toward the organic group(s) in an excited state. MLCT transitions are associated with a large change of the molecular permanent electric dipole moment, Δμ (up to 30 debye, D), that, in turn, is instrumental for achieving high second-order nonlinear susceptibility ,,, and also contributes to charge separation and charge-transport properties. − Interestingly, prominent first hyperpolarizability is routinely observed not only in noncentrosymmetric organometallic structures but also in nominally centrosymmetric structures. ,,, Such obvious spontaneous symmetry breaking was tentatively associated with steric distortions of the ground-state molecular structure, , even though quantitative explanation has so far been lacking.…”