Study On The Properties Of Aggregation-induced Emission And Liquid Crystalline Of Pyrrolopyrrole-Based Derivatives

The solid-state applications of traditional fluorescent materials are more limited due to the aggregation caused quenching effect（ACQ）.In 2001,Tang group proposed the concept of aggregation-induced emission（AIE）when studying the fluorescent behavior of hexaphenylsilole（HPS）,which provided a good opportunity for the application of organic fluorescent materials in the solid state.AIE molecules generally exhibit strong fluorescence in aggregated or solid state as compared to the previous ACQ molecules.Liquid crystal is a kind of soft material between the mobile phase and the order of functional state.Liquid crystal attracts more attention because of its wide use in optical information display and storage devices.However,the conventional liquid crystal materials are non-luminescent.They require extra backlight when used for display devices.In addition,the use of polarizers makes the energy consumption of the device very high.In recent years,the aggregation-induced emission liquid crystal（AIE-LC）material has aroused great concern and extensive research.AIE-LC material has both AIE properties and liquid crystal properties.It can be applied to a very wide range of fields,such as light-emitting diodes,organic polarization lasers,light-emitting liquid crystal displays,information memory,sensors,semiconductors and many other fields.Therefore,the emergence and development of a new type of AIE-LC material has become an urgent need for researchers to make technological breakthroughs in this field.Based on the previous research of our group,two kinds of pyrrolopyrrolederivatives were designed and synthesized named diethyl 4,4’-（2,5-diphenyl pyrrolo[3,2-b]pyrrole-1,4-diyl）dibenzoate（DPP-2COOCH₂CH₃）,bis（2-（acryloyloxy）ethyl）4,4’-（2,5-diphenylpyrrolo[3,2-b]pyrrole-1,4-diyl）dibenzoate（DPP-2CH=CH₂）.The chemical structures of the compounds were characterized by means of ¹HNMR and MS.The main contents and conclusions of this thesis are as follows:First of all,as the core of pyrrole molecules,pyrrolopyrrole derivative molecule named DPP-2COOCH₂CH₃ modified by alkyl chains were synthesized successfully.This compound exhibits typical AIE properties in tetrahydrofuran（THF）/water（H₂O）and THF/hexane systems due to its restriction of intramolecular motions（RIM）mechanism.Then,the concept of AIE was introduced into the design of liquid crystal molecules.The DPP-2CH=CH₂ molecule was designed and synthesized,which has both AIE and liquid crystal properties.This compound also showed typical AIEcharacteristics both in THF/H₂O system and THF/hexane system.The thermal decomposition temperature measured by TGA was at 390 ^oC,which means the DPP-2CH=CH₂ has good thermal stability.By the means of Differential Scanning Calorimetry（DSC）,it was observed two endothermic peaks appear in the heating process at 154 ^oC and 167 ^oC.Combined with Polarizing Optical Microscopy（POM）,it was observed that the focal conic texture of liquid crystal was observed when the temperature was raised to 154 ^oC and the temperature was lowered to 140 ^oC.The results show that DPP-2CH=CH₂ forms a liquid crystal phase in the temperature range from 154 ^oC to 167 ^oC.According to the POM photograph,it is presumed that it may form a smectic texture crystal and continue to cool to form crystals.Fluorescence properties of DPP-2CH=CH₂ in the liquid crystal phase were investigated.We found that with the increase of temperature from 20 ^oC to 150 ^oC,the emission wavelength does not change,but the fluorescence intensity decreased obviously.This is because the molecule consumes excited state energy so that the higher the temperature,the more quenched the fluorescence.When the temperature rises to 150 ^oC～170 ^oC in the liquid crystal region,the emission wavelength blueshifts suddenly.The results show that the temperature range of 150 ^oC～170 ^oC is very close to that of DSC（154 ^oC～167 ^oC）.Therefore,the change of fluorescence intensity and wavelength of fluorescence spectroscopy is expected to be used to characterize the liquid crystal phase transition of liquid crystal molecules.