Study On Phototunable Cholesteric Liquid Crystal Doped By Chiral Fluorescence Photoswitch Based On FRET

Among stimuli-responsive systems of dynamic fluorescence tunable materials,fluorescence resonance energy transfer(FRET)provides a powerful mean for various fluorescent colors via accurately tuning emission spectrum composed of two or more emitters by modulating the ratio and distance between the donor and acceptor components.In this thesis,the first case of dynamic luminescent liquid crystal(LC)with cholesteric helical superstructure through FRET has been prepared,irreversible and reversible phototuning systems respectively.And the main research contents are listed as follows:1.Phototunable cholesteric liquid crystal based on irreversible FRET systemA dicyanodistyrylbenzene-based chiral fluorescence photoswitch(switch 1)has been synthesized.The switch 1 emits bright green and undergoes an irreversible isomerization upon 450 nm blue light irradiation,leading to intensity decreases of both absorption and fluorescence main peaks.A blue fluorescent dye,9,10-diphenylanthracene(DPA),is selected as donor to occur FRET process from DPA to switch 1.The fluorescent color of the LC can be irreversibly tuned from green to blue after irradiated by 450 nm blue light.2.Phototunable cholesteric liquid crystal based on reversible FRET systemA novel chiral fluorescence photoswitch based on 1,2-dithienyldicyanoethene(switch 2)has been synthesized.The switch 2 exhibits orange-red emission and reversible photoisomerization under 520 nm/365 nm light irradiation.An efficient donor-acceptor pair is constructed in LC host by employing a green fluorescent dye coumarin 6(C6)and switch 2 used as a donor and an acceptor,respectively.The fluorescent color of this LC material can be dynamically and reversibly tuned from orange to green when exposed to visible or UV light.In summary,two kinds of irrevers ible/revers ible phototuning of luminescent cholesteric liquid crystals based on FRET are studied respectively.These liquid crystal materials have important applications in display devices,anti-counterfeiting,information encryption,etc.