Fluorescent Liquid Crystal Nanoparticles Based On Dicyanodistyrylbenzene Luminescent Unit And Their Fluorescence Photoswitching Mechanisms

Liquid crystal nanoparticles(LCNPs)is a kind of multifunctional liquid crystal materials on the nano scale.The liquid crystals'orientation behavior,stimuli responsiveness(including electric fields,magnetic fields,and light)and fixed orientation in LCNPs make it a great potential for biomedical and optical applications.In this work,we prepared a kind of photoswitchable fluorescent liquid crystal nanoparticles by the miniemulsion polymerization technique,and some studies on morphology and photoproperties of fluorescent LCNPs were carried on.And it is further patterned by inkjet printing technology to study its application in information encryption and fluorescent anti-counterfeiting.Firstly,we designed and successfully prepared a novel polymerizable dicyanodistyrylbenzene-based fluorescent monomer.Then it was introduced into the polymerizable liquid crystal monomer together with the diarylethene(DAE)photosensitive molecule to prepare a kind of photoswitchable fluorescent LCNPs by the miniemulsion polymerization technique.Studies have shown that the increase of the proportion of DAE increases the contrast of the photoswitch property but has an adverse effect on the LCNPs formation,and a small increase in the ratio of the liquid crystal monomer can stabilize the particles formation.So a suitable proportion of components was finally determined to prepare the water-dispersed,uniform spherical LCNPs with the diameter of 120 nm.Next,some studies on photoswitchable fluorescent properties of LCNPs were carried on.The LCNPs have a bright green fluorescent at 510 nm excitated by 365 nm UV light.Especially,the intensity of florescent of LCNPs have a 88.2%reduction after irradiation of UV(365 nm,2wm/cm2)for 70s,and returned to initial fluorescence intensity after visible light exposure for 30s,as a result of fluorescence resonance energy transfer(FRET)in DAE derivatives and dicyanodistyrylbenzene-based fluorescent monomer.It was identited that there was no loss of fluorescence intensity after many cycles of exposure.And a water-soluble fluorescent ink is prepared based on fluorescent LCNPs and then ink-jet-painting was introduced to prepare the fluorescent patterns on the substrate.The fluorescent patterns show a a dynamic photoswitch progress of "visible/invisible" under visible light,and fluorescent "ON/OFF" under UV light.The fluorescent arrays with such photoswitchable properties have potential applications in the field of information encryption and anti-counterfeiting.Finally,the cells were fluorescently stained with LCNPs,it was found that LCNPs can enter the cells through cell phagocytosis,have extremely low biotoxicity.This work has opened up new ideas for the preparation and functionalization of liquid crystal nanomaterials,and provides important reference value for the application of such materials in the field of biological fluorescence imaging,information display and recording.