Preparation Of Photoresponsive Luminescence Liquid Crystal Materials And Study On Polarized Fluorescence Properties

In recent years,the controllable polarized luminescence has aroused great interest in scientific researchers and rapidly developed into a research hotspot of the optical field due to its potential application value in the 3D optical display,optical encryption and anti-counterfeiting,optical data storage,and optoelectronic devices.To the best of our knowledge,the new type of achiral or chiral functional materials based on α-cyanodiarylethene-based fluorescent molecules not only possess excellent optical properties such as high-efficiency luminescence characteristics and typical aggregation-induced emission enhancement effect but also have sensitive stimulus responsiveness;thus,these fluorescent molecules have shown unique superiority and infinite charm in terms of linearly polarized luminescence(LPL)or circularly polarized luminescence(CPL).In this paper,we designed and synthesized a series of novel α-dicyanodistyrylbenzene fluorescent photoswitches,further constructed their corresponding liquid crystal(LC)systems with polarized luminescence performance,and systematically explored their performance of photoresponsiveness,polarized fluorescence,and related applications.1.A new achiral α-dicyanodistyrylbenzene fluorescent photoswitch(DCN-M)with photoisomerization performance and linearly polarized luminescence performance was designed and synthesized,and it was incorporated into the LC system to obtain liquid crystal polymer films through photopolymerization.Initially,on the basis of the fluorescence dichroism of DCN-M and its synergetic orientation with LC molecules,the first LPL-mode pattern was prepared by utilizing photoalignment technology to control the molecular orientation of the LC system;secondly,the second photoisomerization-mode fluorescent pattern was obtained based on the Z/E photoisomerization of DCN-M,in which molecular configuration transformation led to the fluorescence intensity attenuation;finally,we obtained the LCP with dual-mode fluorescence patterns,which could be read under the linearly polarized or non-polarized ultraviolet(UV)light so as to achieve the purpose of information protection.In addition,in order to facilitate its practicability,a high-resolution dual-mode fluorescent pattern was further prepared on a flexible substrate,which is expected to be used in information anti-counterfeiting and advanced encryption.2.We designed and synthesized two new chiral fluorescent photoswitches with binaphthyl and α-cyanoethylene groups as the central skeleton and electron-donating group and electron-withdrawing group respectively,namely switch 1 and switch 2,and explored their physical properties thoroughly.The research results show that both photoswitches have good solubility in tetrahydrofuran(THF),and can occur reversible Z/E isomerization with good fatigue resistance upon the irradiation of blue and ultraviolet light.Then,we mixed the two photoswitches into the LC small molecule system to prepare cholesteric liquid crystal(CLC)devices and investigated deeply their chiral inducing ability and the photo-response of CPL.The results showed that both have strong chirality-inducing ability and photo-responsiveness.However,by contrast,it is found that the helical twisting power(HTP)value of the switch1-constructed LC system is very small in the initial state.Especially,the HTP value of the LC system approaches zero at a lower concentration(0.2 wt%),while it would greatly increase under the irradiation of UV light or blue light.Thus,photo-switching from LPL to CPL can be realized through the phase transition from the nematic phase to the cholesteric phase.3.Two α-cyano substituted diarylethylene chiral(S)fluorescent hydrogen bond acceptors(acceptor 1 and acceptor 2)were designed and synthesized.The essential difference between the two is the different location of their cyano groups on the C=C bonds;Next,a non-fluorescent hydrogen bond donor molecule with a binaphthyl(R)as the chiral source that opposite to the chirality of acceptor molecules was synthesized;Finally,two hydrogen-bonded chiral fluorescent photoswitches,namely(R,S,R)-switch 1 and(R,S,R)-switch 2,were constructed by means of hydrogen bond assembly.After that,we further explored the structural properties and the photo-responsiveness of the two hydrogen-bonded chiral fluorescent photoswitches in the solution and LC system,respectively.By contrast,it is found that the two photoswitches exhibited excellent photoresponsive performance,and their degree of photoisomerization can be quantitatively controlled by 365 nm and 450 nm lights.Interestingly,based on this feature,we have realized the control of CPL intensity in the(R,S,R)-switch 2 constructed LC system;meanwhile,chirality disappearance and polarization reversion of CPL have been achieved in the LC system constructed by(R,S,R)-switch 1,which exhibits more diverse phototuning effects,and the multi-mode polarized fluorescent binary code pattern was further fabricated according to this characteristic.In this article,in view of the characterization and analysis of the photoresponse performance for this series of new photoswitch molecules above,we successfully constructed three different types of polarized luminescent LC systems,in which the photo-regulation of multi-mode polarized fluorescence can be achieved.It provides new ideas for information storage and information encryption.