Synthetic, Mesomorphic, and DFT Investigations of New Nematogenic Polar Naphthyl Benzoate Ester Derivatives

Abstract

Four new non-symmetrical derivatives based on central naphthalene moiety, 4-((4-(alkoxy)phenyl) diazenyl)naphthalen-1-yl 4-substitutedbenzoate (I_n/x), were prepared, and their properties were investigated experimentally and theoretically. The synthesized materials bear two wing groups: an alkoxy chain of differing proportionate length (n = 6 and 16 carbons) and one terminal attached to a polar group, X. Their molecular structures were elucidated via elemental analyses and FT-IR and NMR spectroscopy. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) were carried out to evaluate their mesomorphic properties. The results of the experimental investigations revealed that all the synthesized analogues possess only an enantiotropic nematic (N) mesophase with a high thermal stability and broad range. Density functional theory (DFT) calculations were in accordance with the experimental investigations and revealed that all prepared materials are to be linear and planar. Moreover, the rigidity of the molecule increased when an extra fused ring was inserted into the center of the structural shape, so its thermal and geometrical parameters were affected. Energy gap predictions confirmed that the I_16/c derivative is more reactive than other compounds.

Keywords: DFT; azo/ester; fused ring; liquid crystals materials; mesomorphic properties; optimized structures; thermal parameters.

Scheme 1

The synthetic compounds, I_n/x.

Scheme 2

Synthesis of 4-((4-(alkoxy)phenyl)diazenyl)naphthalen-1-yl 4-substitutedbenzoate, I_n/x.

Figure 1

¹H NMR of 4-((4-(hexyloxy)phenyl)diazenyl)naphthalen-1-yl 4-methoxybenzoate I_6/a as a prototype.

Figure 2

The second heating and cooling scan of a compound I_6/a DSC thermogram at a heating rate of 10 °C min⁻¹.

Figure 3

Nematic textures under POM on heating of the compound I_16/c at (a) 130.0 °C and (b) 150.0 °C.

Figure 4

DSC transitions of the derivatives, I_n/x.

Scheme 3

Molecular structures of series II_n/x and III_x/n.

Figure 5

Optimum structures for molecules of the derivatives I_n/x, calculated at a B3LYP/6–311G** level.