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The synthesis, spectroscopic and electrochemical data of donor-acceptor-donor tetrazines containing ferrocene moieties and phenyl unit as a [pi]-bridge are presented. The ultraviolet (UV)-vis spectroscopic and cyclic voltamperometric results have indicated sizable intramolecular charge transfer interactions in the ground state when the ferrocene is directly bound to the tetrazine and have shown reduction of the electron-donor strength of ferrocene moieties when there is a phenyl linkage.

The second-order nonlinear optical (NLO) properties of [Ln[(hfac).sub.3](diglyme)] (hfac = hexafluoroacetylacetonate, diglyme = bis(2-methoxyethyl)ether, Ln = La, Ce, Pr, Sm, Eu, Gd, Er, Lu) complexes are examined for providing evidence for the relevant role of f electrons in tuning the second-order NLO response dominated by the octupolar contribution. The lanthanide NLO chromophores have allowed a clean valuation of the affect of f electrons on the quadratic hyperpolarizability and on its dipolar and octupolar contributions.

The second-order nonlinear optical (NLO) properties of [Ln(hfac)3(diglyme)] (hfac = hexafluo- roacetylacetonate; diglyme = bis(2-methoxyethyl)ether; Ln = La, Ce, Pr, Sm, Eu, Gd, Er, Lu) complexes have been investigated by a combination of electric-field second harmonic generation (EFISH) and harmonic light scattering (HLS) techniques, providing evidence for the relevant role of I electrons in tuning the second- order NLO response dominated by the octupolar contribution. These lanthanide NLO chromophores allow a clean valuation of the influence of f electrons on the quadratic hyperpolarizability and on its dipolar and octupolar contributions. Molecular quadratic hyperpolarizability values measured by the EFISH method, βEFISH, initially increase rapidly with the number of f electrons, the value for the Gd complex being 11 times that of the La complex, whereas this increase is much lower for the last seven f electrons, the βEFISH value of the Lu complex being only 1.2 times that of the Gd complex. The increase of (βHLS), which is dominated by an octupolar contribution, is much lower along the Ln series. Remarkably, the good (βHLS) values of these simple systems, well known for their luminescence properties, are reached at no cost of transparency. [ABSTRACT FROM AUTHOR]