Theoretical investigation of the effect of a spin transition on the second-order molecular hyperpolarizability of a bis(salicylaldiminato)FeII Schiff base complex

The intermediate neglect; of differential overlap-based (INDO-based) sum-over-states (SOS) perturbution theory and the density functional theory (DFT) are used to explore the effect of a spin-crossover phenomenon on the quadratic molecular NLO response (beta) of an (FeL)-L-II complex in which the Hat ligand is obtained from the Schiff base condensation of 5-nitrosalicylaldehyde with 1,4,7,10-tetraazadecane. The calculations based on crystal structures recorded at different temperatures reveal that the spin transition results in a beta increase of about 25% of its initial value. This effect is mainly due to geometry modifications occurring upon spin transition. In addition, a temperature dependence of beta is also pointed out for the first time.