An extending evidence of molecular conformation on spectroscopic properties of symmetrical bis-Schiff bases

The relationship between the molecular conformation and spectroscopic properties of symmetrical bis-Schiff bases, was explored experimentally. The synthesis, crystal structures, and spectroscopic behaviors of symmetrical bis-Schiff bases derived from 1,4-Phthalaldehyde, p-YC6H4NCHC6H4CHNC6H4p-Y (Y = OMe, Me, H, Cl, or F) were reported. The results show when the effect of distance between X or Y and the imine carbon was considered, a good correlation between the υmax or δC(CN) of symmetrical bis-Schiff bases and the substituent parameters was obtained. The correlation results indicate that for both symmetrical bis-Schiff bases derived from 1,4-Phenylenediamine and 1,4-Phthalaldehyde, the UV absorption spectrum is dependent on the substituent at the aniline ring and the dihedral angle τ, and the term sin(τ) is suitable to modify the substituent effects on the υmax. However, experimental investigations indicate that the dihedral angle τ has a limited effect on the values of δC(CN). This study provides an extending evidence of molecular conformation effects on spectroscopic properties of symmetrical bis-Schiff bases.