Synthesis And Properties Of Novel BODIPY Fluorescent Dichroic Liquid Crystal Dyes

The structure of boron-dipyrromethene?BODIPY?has developed rapidly in the field of organic functional materials due to its excellent photophysical properties.In this paper,the functional groups were introduced at the 8 and 2,6 active sites of BODIPY,respectively,three synthesized series of fluorescent dichroic liquid crystal dyes are identified by ¹H NMR,¹³C NMR and HRMS;based on the Guest-Host?G-H?effect,the synthesized dyes can exhibit anisotropy to light absorption and fluorescence emission after being mixed with the liquid crystal materials;in order to get deeper application in the field of information display,the test data including liquid-crystalline properties,threshold voltage and response time of all compounds are analyzed and discussed.The maximum absorption wavelength and the maximum emission wavelength of dye DPA containing bisphenylacetylene structure in isotropic solvents are not much different from the corresponding values tested in the host liquid crystal,which are concentrated at about 505 nm and 526 nm,respectively;the molar extinction coefficient is close to 10⁵,which belong to the strong absorption range;wherein,the absorption ordered parameter S_A of DPA-1 is 0.7,and the fluorescence ordered parameter S_F is 0.67;dye DPA-2 has liquid crystal phases in the temperature range of 251.0-272.0?,and the response time measured after compounding with the host liquid crystal E7 is reduced by 22.6%compared with the value of the liquid crystal E7.Dye DC based on 8-position modified bicyclohexyl structure whose half-width of fluorescent peak is narrow emits green fluorescence,and the maximum polarization absorption peak is concentrated at about 506 nm,the fluorescence polarization maximum emission peak is concentrated at about 525 nm;dye DC-2 has the dichroic ratio D_A of 8.91and the ordered parameter S_A of 0.73;according to liquid-crystalline properties tests,dye DC-3 and DC-4 showed liquid crystal texture during heating and cooling;after voltage energization,the threshold voltage of the mixture of dye DC and the host liquid crystal E7 is better than the corresponding value of the liquid crystal E7.Furthermore,DC-3+E7 has the fastest response time in this series,which is 15.8%lower than the corresponding value of E7under the same conditions.The polarization spectrum test shows that the maximum emission wavelength of dye SY based on the 2,6-modified symmetrical structure which emits orange or red fluorescence is concentrated in the range of 558-629 nm;the dichroic ratio of dye SY-4 is up to 12.26 and the ordered parameter is up to 0.79,which is the maximum of the three series;tested by DSC and verified by POM,SY-2 and SY-3 have liquid crystal phases in the range of 143.3-185.8?and 171.6-260.9?during the cooling process,respectively.Dye SY-4 has smectic phases and nematic phases during heating and cooling process;the threshold voltage of SY-3+E7 is 1.48V,which is 10%lower than that of the liquid crystal E7;dye SY-4 reduced the response time by 8.31 ms,reducing the response time of the host liquid crystal E7 by 17%.