Study On Blue Phase Liquid Crystal Devices Based On Aggregation Induced Luminescence Materials

Blue Phase Liquid Crystal(BPLC)has many unique optical properties,such as selective reflection,circular dichroism,optical rotation,fast response and so on,due to its double twisted helix and periodic structure.One of the most important features is selective reflection of Circularly Polarized Light(CPL).Because CPL has a broad application prospect in the future display and photonics technology,and using BPLC is an ideal way to directly generate CPL,this has aroused the interest of researchers in BPLC research.However,the BPLC itself does not emit light,and CPL emission sources and traditional reflective LCDs made with it usually require external light sources.In addition,color filters and polarizers are required,which are very energy consuming due to their limited transmission of incident light.To solve this problem,researchers considered combining fluorescent materials with BPLCs to make self-luminous BPLCs.However,traditional fluorescent materials have the problem of light quenching caused by aggregation,that is,when the doping concentration of fluorescent materials is too high,the light will be quenched.At present,some fluorescent materials with the properties of aggregation-induced emission(AIE)have been developed,such as Silole derivatives,tetraphenylethylene derivatives,etc.In order to develop a BPLC display material capable of emitting CPL efficiently,it is an effective way to combine AIE effect fluorescent material with BPLC.In this dissertation,the temperature domain,texture and luminescence properties of the blue phase of the mixture of tetrapenylvinyl-propyl phenyl vinyl(TPE-PPE)and BPLC(LEBPLC)with different proportions of AIE materials were studied,and the effects of the concentration of TPE-PPE,temperature,phase state and cell gap on the luminescence properties of LE-BPLC were also studied.It is found that the blue phase temperature domain of LE-BPLC does not increase or decrease obviously with the change of doping ratio of TPE-PPE.Moreover,the texture of LE-BPLC changes with the change of temperature,and at macro level,it successively reflects the visible blue,green and red colors.The higher the concentration of TPE-PPE,the more obvious the AIE effect and the higher the fluorescence intensity.The lower the sample temperature,the stronger the fluorescence of LE-BPLC;When LE-BPLC is in BP state,the luminescence capacity is the highest,and the absolute value of the luminescence asymmetry factor is more than 0.28;Due to the superposition effect of light,the cell gap is proportional to the fluorescence intensity.Secondly,in order to explore the possibility of making LE-BPLC into display device,the influence of the concentration of TPE-PPE and cell gap on LE-BPLC electro-optical performance was also studied in this thesis.It was found that the driving voltage of the sample was not affected by the concentration of TPE-PPE.Cell gap is the key factor affecting the driving voltage of LE-BPLC,which is manifested as the smaller the cell gap is,the smaller the driving voltage is.It is also found that the absolute value of the luminescence asymmetry factor of LE-BPLC decreases with the increase of electric field.Finally,a BPLC display method of liquid crystal molecular orientation controlled by electric field is proposed.The LE-BPLC developed in this project can efficiently emit CPL,and can also be used to make the emission source of CPL.The value of this thesis lies in providing a novel method to fabricate and obtain CPL emitter and LE-BPLC display devices.This kind of device has the advantages of simplified manufacturing process and low energy consumption,and has great potential in the future manufacturing of energy-saving LCD.