Synthesis and liquid crystalline properties of hydrazide derivatives: hydrogen bonding, molecular dipole, and smectic structures

A series of dissymmetric hydrazide derivatives with amino terminal group, N‐(4‐alkoxybenzoyl)‐N′‐(4′‐aminobenzoyl) hydrazine (Cn‐NH2, n indicates the number of carbon atoms), were designed and synthesised, and their liquid crystalline properties were investigated by means of differential scanning calorimetry, polarised optical microscopy, and wide‐angle X‐ray diffraction. It was found that these materials showed a SmAd phase, and intermolecular hydrogen bonding was confirmed as the driving force. Moreover, these results were further compared with those of their parent compounds, N‐(4‐alkoxybenzoyl)‐N′‐(4′‐nitrobenzoyl) hydrazine (Cn‐NO2) and the dimers, α, ω‐bis [N‐(4‐nitrobenzoyl)‐N′‐(benzoyl‐4′‐oxy) hydrazine] alkane (Nn), and the effect of hydrogen bonding, dipole‐dipole interactions on the smectic structures is discussed.