Fascinating role of the number of f electrons in dipolar and octupolar contributions to quadratic hyperpolarizability of trinuclear lanthanides-biscopper Schiff base complexes.

The trinuclear [Ln(NO3)3(CuL)2] complexes (Ln = La, Ce, Sm, Eu and Er, L = N,N′-1,3-propylen-bis(salicylideniminato) have been investigated by a combination of HLS and EFISH techniques to evaluate both the dipolar and octupolar contributions to their significant quadratic hyperpolarizability and to confirm that f electrons may tune their second-order NLO response. In the complexes investigated, the major contribution to the total quadratic hyperpolarizability is largely controlled by the octupolar contribution, but the values of both βEFISH and ∥βJ=1∥, that is the dipolar part, are significantly influenced by the number of f electrons, confirming that the unexpected polarizable character of f electrons may be the origin of such fascinating evidence.