Preparation Of Fast Response Liquid Crystals For Wavefront Corrector

Liquid crystal wavefront corrector(LCWFC) is a core component of adaptiveoptics system(AOS), used to achieve real-time compensation for optical wavefrontdistortion, and its direct impact on the performance of adaptive optics imagingsystem. The liquid crystal(LC) adaptive optics system requires wavefront correctorwith fast response performance, usually kHz magnitude, namely sub-millisecondresponse time. The response speed of the LC device mainly related to the LCmaterials used therein, which Can achieve fast response to the nematic LC materialmust have the properties of high n value and low viscosity. Generally speaking, LCcompounds with high n value necessarily have long π-electron conjugated system,increase in the length of the π-electron conjugated system will lead to increase theviscosity of the LC material. Therefore, obtained LC material with high n value andlow viscosity is a problem in the research of liquid crystal materials.Firstly, making a literature survey about high n value and low viscosity LCmaterials, comprehensive comparison and analysis of the literature and found thatphenyl tolane isothiocyanate compounds almost have these two properties at thesame time, but still can not meet the current demand. In order to further improve theresponse speed of the LC material, this paper studies the following two areas:(1)Design and synthesis of phenyl tolane isothiocyanate compounds with high n valueand low viscosity characteristics, and then study its liquid crystal properties;(2) Further increase the number of substituted fluorine atoms based on the structure ofLC compounds with high n value and low viscosity, design and synthesis offluoro-substituted phenyl tolane isothiocyanate LC compounds, and then study itsliquid crystal properties.Secondly, study the preparation and properties of mono-fluoro-substitutedphenyl tolane isothiocyanate LC compounds.(1)Synthesis6kinds ofmono-fluoro-substituted phenyl tolane isothiocyanate liquid crystal compounds, theresults of IR and1HNMR showed that the structure of compounds synthesized isconsistent with the target molecule.(2) The n value of the6kinds ofmono-fluoro-substituted phenyl tolane isothiocyanate LC compounds is0.55to0.65,and n value shows a successively decreasing trend as increasing the number ofcarbon atoms in the terminal groups.(3) The calculation and analysis results of theviscoelastic coefficient showed that after incorporating mono-fluoro-substitutedphenyl tolane isothiocyanate LC compounds with the mass fraction of10%in the9023commercial alkyne LC material, the viscoelastic coefficient of mixed LCmaterial is not significantly higher than the viscoelastic coefficient of9023commercial alkyne LC material.(4) The research of the phase transition temperatureshowed that the LC compound (n-propyl end group is excluded) began to melt atabout90℃when the fluorine atom in2nd position, the LC compound began tomelt around140℃, when the fluorine atom in3rd position. LC compounds with theterminal group of n-propyl, began to melt into the nematic phase but no smecticphase as the temperature increases. LC compounds with substituted fluorine atom atthe2nd position melt into the nematic phase at about110℃as the temperatureincreases. Replaced by fluorine atoms in the3rd position，as the temperatureincreases above180℃before entering in the nematic phase.(5) The results of theresponse performance FoM value shown that the mixed crystal material,incorporating mono-fluoro-substituted phenyl tolane isothiocyanate LC compoundswith the mass fraction of10%in the9023commercial alkyne LC material,respectively, have significantly higher response performance than9023commercial alkyne LC material. The response performance was increased by14%to24%. Theresponse performance change little when the end groups were n-propyl and thefluorine atom substituted in2ndor3rdposition. The response performance of the LCcompound with substituted fluorine atom at position2is lower than the responseperformance of a fluorine atom at the3-position of the LC compound, when theterminal group is n-butyl and n-pentyl group. The response performance of the3kinds of LC compounds with substituted fluorine atom at position2and differentterminal carbon chain length changed, but the rule of change is not obvious. Theresponse performance of the3kinds of LC compounds with substituted fluorineatom at3-position increased sequentially as the length of the carbon chain increased,but the rate of increase is not large.Once again, research the preparation and properties of multi-fluoro-substitutedphenyl tolane isothiocyanate LC compounds.(1) In order to further reduce theviscosity, lateral fluoro-substituents added on the basis of phenyl tolaneisothiocyanate central structure. Synthesis of five kinds of multi-fluoro-substitutedphenyl tolane isothiocyanate LC compounds, the results of IR and1HNMR showedthat the structure of compounds synthesized is consistent with the target molecule.(2)The n value of the6kinds of multi-fluoro-substituted phenyl tolane isothiocyanateliquid crystal compounds is0.42to0.51, and n value successively decrease asincreasing the number of substituted fluorine atoms in the terminal groups.(3)Themixed crystal material, single crystal material dissolving in9023commercial alkyneLC material with the mass fraction of10%respectively, have higher viscosity than9023commercial alkyne LC material(the compound with n-propyl and substitutedfluorine atom in2-position exceptive).(4) The study of the phase transitiontemperature shown that melting point declined with the increased number of fluorineatoms substituted, trifluoro-substituted LC compound having the lowest meltingpoint.(5)The response performance of phenyl tolane isothiocyanate LC compoundwith n-propyl and two fluorine atoms replacing, is the optimum.The responseperformance of the LC compound with3substituted fluorine atoms is better than the LC compound with4substituted fluorine atoms, consistent with other parts of thestructure.(6) According to the comprehensive analysis of mono-fluorine-substitutedphenyl tolane isothiocyanate LC compounds and multi-fluorine-substituted phenyltolane isothiocyanate LC compounds known that viscoelastic coefficient of the LCcompounds is not as simple as the theoretical analysis with an increase in the numberof substituted fluorine atoms, viscoelastic coefficients dropped, but showing theresults are very complex irregular. This is the nature of liquid crystal compounds cannot be directly predicted from the theory, a more direct and effective data derivedfrom experiments.This paper is an example of organic chemistry and optics applications, frommolecular design to the synthesis of LC compounds, and then to the test ofproperties, this logic to the ideas and methods of further development of fastresponse LC material in LCWFC, provides a good theoretical and experimentalbasis.