Study On Preparation And Phototunable Properties Of Blue Phase Liquid Crystal Based On α-cyanodiarylethene-based Fluorescence Photoswitches

As a unique three-dimensional soft photonic crystal,blue phase liquid crystal(BPLC)has special periodic nanostructures and excellent optical properties.The lattice tunability enables the BPLC lattice constant easy to change and dynamically response to external various stimuli such as temperature,light,electricity and magnetic field,so it has attracted extensive attention in recent years.In this paper,two kinds of photoresponsive BPLC systems were constructed based on achiral and chiral α-cyanodiarylethene fluorescence photoswitches.The prepared fluorescence photoswitches have both ability of trans-cis photoisomerization and excellent luminescence performance under light irradiation.The BPLC systems constructed by them can undergo phase transition or the dynamically tuning of photonic bandgap(PBG)in the visible wavelength band,which accompanies by the tuning of luminescence performance.The main research contents include:1.BPLC based on α-cyanodiarylethene bent-core fluorescence photoswitchesTwo α-cyanodiarylethene bent-core fluorescence photoswitches HB1 and HB2 were synthesized by assembling halogen donors with halogen accepters M1 and M2,respectively.Both fluorescence photoswitches emit orange red fluorescence at the initial state,and undergo reversible photoisomerization under visible and ultraviolet irradiation.Then the BPLC systems were constructed by mixing them with nematic liquid crystal SLC1717 and chiral dopant S811 in certain proportion.The results show that the BP temperature range is broadened to 14 ℃ in A1 system constructed by HB1.In B1 system constructed by HB2,the reversible phase transition between BP and cholesteric(Ch)can be achieved under visible and ultraviolet irradiation at the stable blue phase state,which is accompanied by the tuning of reflection color.Meanwhile,the fluorescence intensity changes due to the variation of the photoswitch configuration.2.BPLC based on α-cyanodiarylethene chiral fluorescence photoswitchesTwo α-cyanodiarylethene chiral fluorescence photoswitches switch 1 and switch 2 were designed and synthesized.Both chiral fluorescence photoswitches emit yellow green fluorescence at the initial state,and undergo reversible photoisomerization under visible and ultraviolet irradiation.Then the BPLC systems were constructed by mixing them with nematic liquid crystal SLC1717 and chiral dopant S811 in certain proportion.The results show that the BP temperature range can be extended after the doping of switch1 or switch 2,and the BP temperature range is broadened to 13.6 ℃ in B1 system constructed by switch 1.In all systems,the reversible contraction and expansion of BP lattice can be realized under visible and ultraviolet irradiation at the stable blue phase state,so as to achieve the reversible tuning of PBG in the visible wavelength band.Meanwhile,the fluorescence intensity can also vary greatly.Furthermore,high-contrast reflectance/fluorescence dual-mode BP patterns are obtained by using photomasks.In summary,photoresponsive BPLC systems are constructed based on α-cyanodiarylethene chiral or achiral fluorescence photoswitches.In these two BPLC systems,the reversible phase transition between BP and Ch and reversible tuning of PBG in the visible wavelength band were achived respectively,accompanied by great change of the fluorescence intensity.The reflection/fluorescence dual-mode BPLC developed in this study has potential application value in the fields of anti-counterfeiting and information encryption.