Study On Phototuning Of Circularly Polarized Luminescence Of Luminescent Cholesteric Liquid Crystals

In recent years,the research of circularly polarized luminescence（CPL）materials has become a hot topic.Many emerging CPL materials have been reported,such as natural macromolecules,chiral liquid crystals（LCs）,small organic molecules,metal complexes,cellulose nanocrystals,synthetic polymers and so on.Constructing cholesteric liquid crystals（CLCs）superstructure systems by incorporating chiral molecules and organic fluorescent molecules into nematic liquid crystals（N-LCs）as well as regulating CPL signals under external stimulation is an important way to investigate CPL materials.In this thesis,the CPL signals of the CLCs are regulated by using light sources with different wavelenth,and two CLCs systems of chiral inversion of CPL signal and significant enhancement on dissymmetry factor(g_lum)of CPL signal are constructed.The specific research content includes:1.Reversible inversion of CPL signal based on CLCsA new type of chiral fluorescent photoswitch（switch 1）based on monocyano substituted diarylethylene was synthesized.The switch 1 can emit bright green fluorescence and undergo reversible photoisomerization under 450 nm and 365 nm light irradiations.Incorporating switch 1 and the right-handed chiral dopant R3011 with the opposite handedness into N-LCs SLC1717 at an appropriate ratio can produce a CLCs system with photoinduced chiral inversion.When irradiated with 450 nm visible light to a steady state,the CPL signal is reversed;and then 365 nm UV light is used for back-irradiation,the rotation direction of the CPL signal comes back,which is accompanied by a significant change of the CPL signal intensity.2.Significant g_lum increasement of CPL signal based on CLCsA new type of chiral fluorescent photoswitch（switch 2）based on diaryldicyanoethene was synthesized.The switch 2 can emit bright yellow fluorescence and undergo reversible photoisomerization under 520 nm and 405 nm visible light irradiations.Both switch 2 and R3011 with right handedness are mixed into the SLC1717 in a certain proportion to construct a CLCs system,in which the reflection band and the emission band match well to achieve significant g_lum increasing of the CPL signal.On the basis of the g_lum increasement,3D CPL pattern could be obtained,which could be erased and rewritten reversibly upon 520 nm and 405 nm light irradiations.In this thesis,two mono/dicyano substituted diarylethene chiral fluorescent photoswitches were designed and synthesized.Two CLCs systems were constructed by doping each of them and R3011 into N-LCs,in which the chirality inversion of CPL signal and significant g_lum increase of the CPL signal could be respectively realized.This work provides a new idea for the study of dynamic tuning and increasing g_lum of CPL materials.