Properties Research Of BODIPY Dichroic Dyes For Guest-host Display

BODIPY fluorescent dyes are widely used in the field of organic functional materials because of exceedingly good photochemical stability and photophysical properties.In this paper,two series of dichroic dyes that used in“guest-host”liquid crystal display were designed and synthesized by introducing functional groups at 2,6sites of BODIPY,the structure of dichroic dyes were proved by ¹H NMR and HRMS.Based on the guest-host（G-H）effect,these series of dichroic dyes exhibit anisotropy in light absorption and fluorescence emission by dissolving in liquid crystal E7.The UV-Vis absorption and fluorescence emission spectroscopy of 2,6-modified H-series dyes in solvent dichloromethane show that the maximum absorption wavelength(λ_max（A）)and maximum emission wavelength(λ_max（F）)are concentrated at563 nm and 600 nm.The molar extinction coefficients of H1 and H2 are higher than5.00×10⁴,which means compound H1 and H2 have strong light-absorbing ability,respectively,the molar extinction coefficient of H3 is only 1.58×10⁴.The fluorescence lifetimes of H-series dyes in dichloromethane and liquid crystal E7 were tested and the curves of time-dependent luminescence decay show that the fluorescence lifetime in liquid crystal E7 was about 2 ns shorter than the values measured in solvent dichloromethane.Dissolving the series dyes of H（guest）in the liquid E7（host）for polarization spectrum test,the absorption dichroic ratio（D_A）of dye H1 is 6.01,and the absorption order parameter（S_A）is 0.63;the values of dye H3 are 9.38 and 0.81,respectively,the value of H2 is lower than the former.The values of dichroic ratio（D_A）and order parameter（S_A）are 4.61 and 0.55.For H1,liquid crystal phase exists in the temperature range of 289.7～305.2°C during heating and of 254.7～265.3°C during cooling process.The UV-Vis absorption and fluorescence emission spectroscopy of 2,6-modified D-series dyes in solvent dichloromethane show that the maximum absorption wavelength(λ_max（A）)and maximum emission wavelength(λ_max（F）)are concentrated at560 nm and 600 nm.The maximum absorption and emission wavelengths of D2 is slightly red-shifted relative to D1,D3;The fluorescence lifetimes of D-series dyes in dichloromethane and liquid crystal E7 were tested and the curves of time-dependent luminescence decay show that the fluorescence lifetime in liquid crystal E7 is shorter than that of dyes in solvent dichloromethane.Dissolving the series dyes of D（guest）in the liquid E7（host）for polarization spectrum test,the values of D_A（6.21）and S_A（0.63）of dye D3 are higher than that of D1 and D2.There is no liquid crystal phase for D1 in the process of heating and cooling,as for dye D2,liquid crystal phase appears in the process of heating,the temperature range is 223.7～285.6℃,the temperature range of liquid crystal phase of D3 in heating process is 256.3～280.7℃.