In this work four metal-organic framework isomorphs, based on fructose and alkali-earth halogenides, were investigated to better understand the effect of the size of the cation and the different polarizability of the anion on the calculated hyperpolarizability and optical susceptibility, which are correlated to non-linear optical properties. The compounds were characterized by X-ray diffraction and the first hyperpolarizability and the second-order susceptibility were obtained from theoretical calculations. Furthermore, a new method to measure the second-harmonic (SH) efficiency on a small quantity of powder at different wavelengths of excitation was optimized and an attempt was made to assess the reduction of the SH intensity for small quantities of nano-crystals, in order to ascertain the possibility of applications in biological systems. The results of this work show that both the intrinsic nature of the anion and the induced dissociation of cations and anions by fructose play a role in the second-harmonic generating properties of such compounds.
Keywords: isomorphic material; metal–organic frameworks (MOFs); non-linear optical properties; second-harmonic generating efficiency; structure–property relationship.