Positional and Charged Effects of Heterocyclic N Atoms on Mesogenic Properties of Stilbazoles and Analogous N-Oxides
摘要:
The synthesis and the phase behavior of stilbazoles and corresponding N-oxides containing different positions of heterocyclic N atoms, i.e. trans-2'-, 3'-, 4'- stilbazoles and their N-oxides, are reported. Their phase transition temperatures and the mesogenic behavior were investigated through the DSC, polarizing optical microscope and X-ray diffraction (XRD) measurements. Increasing dipole moments by oxidation of stilbazoles to analogous N-oxides induces the S-A phase with an interdigitated bilayer packing. Both 2'-stilbazoles and analogous N-oxides do not possess mesogenic phases, which may be due that pi electron polarizabilities an reduced by the molecular twist originated from dipoles along the ortho-direction. Besides, the positonal effects of the N-oxides on mesogenic properties are more distinct than those of analogous stilbazoles, and new mesogenic phases have been generated by tuning the position of the N-oxide function in the charged liquid crystals. Consequently, unique mesogenic properties may he introduced through adjusting the dipolar direction and strength of the heterocyclic atoms in the molecules.
Positional and Charged Effects of Heterocyclic N Atoms on Mesogenic Properties of Stilbazoles and Analogous N-Oxides
摘要:
The synthesis and the phase behavior of stilbazoles and corresponding N-oxides containing different positions of heterocyclic N atoms, i.e. trans-2'-, 3'-, 4'- stilbazoles and their N-oxides, are reported. Their phase transition temperatures and the mesogenic behavior were investigated through the DSC, polarizing optical microscope and X-ray diffraction (XRD) measurements. Increasing dipole moments by oxidation of stilbazoles to analogous N-oxides induces the S-A phase with an interdigitated bilayer packing. Both 2'-stilbazoles and analogous N-oxides do not possess mesogenic phases, which may be due that pi electron polarizabilities an reduced by the molecular twist originated from dipoles along the ortho-direction. Besides, the positonal effects of the N-oxides on mesogenic properties are more distinct than those of analogous stilbazoles, and new mesogenic phases have been generated by tuning the position of the N-oxide function in the charged liquid crystals. Consequently, unique mesogenic properties may he introduced through adjusting the dipolar direction and strength of the heterocyclic atoms in the molecules.