Synthesis, Structural Studies, Theoretical Calculations, and Linear and Nonlinear Optical Properties of Terpyridyl Lanthanide Complexes: New Evidence for the Contribution of f Electrons to the NLO Activity

The synthesis and structural, photophysical, and second-order nonlinear optical (NLO) properties
of a novel lanthanide terpyridyl-like complex family LLn(NO3)3 (Ln = La, Gd, Dy, Yb, and Y) are reported.
The isostructural character of this series in solution and in the solid state has been established on the
basis of X-ray diffraction analysis in the cases of yttrium and gadolinium complexes, theoretical optimization
of geometry (DFT), and NMR spectroscopy. The absorption, emission, and solvatochromic properties of
the free terpyridyl-like ligand L were thourougly investigated, and the twist intramolecular charge transfer
(TICT) character of the lowest energy transition was confirmed by theoretical calculation (TDDFT and CIS).
The similar ionochromic effect of the different lanthanide ions was evidenced by the similar UV−visible
spectra of the complete family of complexes. On the other hand, the quadratic hyperpolarizability coefficient
β, measured by the harmonic light scattering (HLS) technique, is clearly dependent on the nature of the
metal, and a careful examination of the particular case of yttrium unambiguously confirms the contribution
of metal f electrons to the NLO activity.