Light Emission Behavior Of Several Organic Small Molecules Based On Tolane Unit

Liquid crystals(LCs) have found a wide range of applications in high-tech fields,especially in panel display devices. However, because the conventional LCs are non-emissive, the application of LC displays still have disadvantages which are caused by the use of unpolarized backlight. It is expected that luminescent liquid crystals(LLCs)can overcome such shortcomings. The LLCs combined with intrinsic light-emitting capability and spontaneous self-organization behavior at a liquid crystalline phase may emit linear or circular polarized light, which may be applied for the construction of the lighting and orientating layers in LC display devices.Herein, an achiral compound and three chiral liquid crystals derived from tolane were designed and synthesized. The self-assembly behaviors of the achiral compound were studied using field-emission scanning electron microscopy. It was found that the compound exhibited spontaneous resolution behavior. Its morphology was controllable by changing temperature and concentration. UV-vis and fluorescence spectra indicated that it remained aggregation-induced emission characteristic in acetonitrile/water mixtures. It showed blue fluorescence with an emission band at 456 nm in pure acetonitrile. When fw was above 90%, the emission band blue-shifted to 394 nm and the intensify was 3 times higher than that in pure acetonitrile solution. For the other three chiral liquid crystals, BP Ⅱ, TGBA*, cholesteric and smectic phases were identified using polarized optical micrography and differential scanning calorimetry. Circular dichroism spectra indicated that the helical pitch of chiral lamellar structure decreased with increasing the temperature, and BPⅡ had a double twist arrangement. X-ray diffraction crystallography showed π-π and CH-π interactions among the molecules. This series of molecules have obviously crystallization-induced emission enhancement characteristics at crystalline state and fluorescence emission behavior at liquid crystalline ones. Cholesteric and blue phases with high electromagnetic response speed have found applications in LC display devices.