Second-Harmonic Generation within the P212121 Space Group, in a Series of Chiral (Salicylaldiminato)tin Schiff Base Complexes

A series of 10 (211) new chiral (salicylaldiminato)tin Schiff base complexes obtained from the Schiff base condensation of 4-(diethylamino)salicylaldehyde and various amino acids, in the presence of diphenyltin oxide, is reported together with the parent achiral (1) derivative. Compounds 27 crystallize in the P212121 orthorhombic space group, and their quadratic nonlinear optical properties are investigated. At the molecular level, the derivatives possess similar electronic spectra (λmax ≈ 395 nm), and hence molecular hyperpolarizabilities (β), in relation to the same π-conjugated “push−pull” electronic structure. In the solid state, they exhibit efficiencies in second-harmonic generation (SHG) up to 8 times that of urea. The SHG intensities of chromophores 26 appear largely correlated with a simple “degree of chirality” (dχ) parameter, defined from the molecular geometries. The intriguing issue of a possible quantification of chirality by means of SHG measurement is addressed.