Influence of Structural Features of Azo-, Azoxy-, Azodioxy-Benzenes and Pyridines on Mesomorphic Properties of Systems on their Basis

Abstract

. The DFT/B3LYP/cc-pVTZ method was used to determine geometric parameters, electronic and vibrational characteristics of trans-isomers of azo-, azoxy-, azodioxy-benzene and azo-, azoxy-pyridine, which can act as precursors for synthesis of individual compounds or as components of supramolecular complexes with mesomorphic properties. It has been shown that azo-, azoxy-, and azodioxy bridging groups are electron accep-tors with respect to phenyl and pyridine fragments. The effect of the oxygen atom number in bridging group on the properties of molecules is estimated. The internal rotation potential functions U( φ ) and torsional vibration amplitudes of phenyl and pyridine fragments, leading to distortion of planar structure of molecules, are calculated. A correlation between the calculated function U( φ ) and the distribution diagram of the torsion angle φ (CCNN) in the –Ph–N=N–Ph– fragment among the conformations stabilized in crystals is shown. It is assumed that in the Ph–N=N–Ph molecules possessing a larger amplitude of phenyl (Ph) torsional vibrations than the molecules with azoxy- and azodioxy-groups, the appearance of short-range disorder in the crystal at a lower temperature can be expected. For the Ph1–N(O)–N–Ph2 compounds, the asymmetry of molecular core and different amplitudes of torsional vibrations of the phenyl fragments Ph1 and Ph2 could be the reason for the expansion of mesophase existence temperature range ∆Т . The data obtained for the reference molecules make it possible to predict conformational properties and structural non-rigidity of numerous mesomorphic compounds containing the studied fragments.