Hydrogen bonded liquid crystals from nitrophenols and alkoxystilbazoles

Three series of hydrogen bonded adducts have been formed between 4-alkoxy-4'-stilbazoles dagger and the nitrophenols 4-nitrophenol, 3-nitrophenol and 2,4-dinitrophenol. Each series is mesomorphic displaying both nematic and smectic A phases, in sharp contrast to the behaviour of the individual components. The binary phase behaviour of mixtures of 3-nitrophenol and 4-octyloxystilbazole is reported, and gives conclusive evidence for the formation of a one-to-one hydrogen bonded adduct. Electronic spectroscopy of 2,4-dinitrophenol/decyloxystilbazole was very informative and showed that the higher energy, ionic hydrogen bonded state, corresponding to proton transfer, was significantly populated through the mesophase, and that the mesophase provides an additional stabilisation for this state.