Study On Cynodiarylethene-Based Chiral Fluorescence Photoswitches And Photoresponsive Liquid Crystals

Liquid crystal(LC)materials have received a great deal of attention due to their special optical anisotropy and tunability under external fields.Towards this end,self-organized helical superstructures,i.e.,cholesteric liquid crystals(CLCs),which exhibit a plethora of fascinating functionalities such as circular dichroism,selective reflection and optical activity.Cholesteric LCs are generally fabricated by adding chiral dopants as chirality inducing guests to achiral nematic host materials.And introducing photoresponsive moieties and other fluorophores into the LCs may bring about more possibilities on potential technological applications and functions.In this thesis,we designed and synthesized a series of photoresponsive chiral switches with fluorescence as CLC dopants,and prepared photoresponsive CLC materials with different fluorescence.The photoresponsive behaviors and the physical properties are discussed and the main research contents are listed as follows:1.Two dicyanodistyrylbenzene-based chiral photoswitches(S,S)-3 and(R,R)-3 with opposite chirality were designed and synthesized.By characterization,the photoresponsive behaviors are studied and the experimental results show that these switches are sensitive to ultraviolet(UV)light.Their main absorption peaks are around 365 nm and the switches can emit brilliant bluish green light under UV light.lrreversible Z/E isomerization occurs under UV irradiation and the steric configuration of the switche alters drastically so as to induce large variation of the HTP value.Meanwhile,the fluorescence intensity of the switches become nine times weaker after the isomerization,which can be easily recognized by naked eyes.We doped this chiral photoswitch to induce CLCs,enabling a reflection spectral shift of more than 1500 nm under UV light with conspicuous fluorescence var:iation.Such CLC materials are used to prepare flexible UV sensor where the reflection color changes under ultraviolet of different intensity.2.Two UV/vis sensitive chiral fluorescence photoswitch with partial reversibility,namely MS-1 with thiophene moieties and MS-2 without thiophene moiety,were prepared.By contrast,the structure of thiophene moiety benefits to the reversible isomerization that the one with thiophene moiety(MS-1)has a better reversibility,which makes it an excellent photoswitch with higher performance.It is found that the partially reversible Z/E isomerization of MS-1 in solution takes place when it is under 365 nm/450 nm light irradiation,and the HTP value changes with the fluorescence intensity getting 2.5 times weaker.Transparent LC display device with fluorescence and fluorescence/reflection containing photoswitch MS-1 with different concentration was prepared.Upon exposure to UV/vis light,we can reversiblely write/erase patterns with fluorescence and reflection for many times,and using a handy laser pointer is enough to record information in daily life.3.A non-UV driving 1,2-dithienyldicyanoethene based chiral fluorescence photoswitch 2B2TDCE was prepared.Appling blue/green light irradiation on the solution of 2B2TDCE can trigger the reversible Z/E isomerization and the switch can also recover in high temperature.It is found that such molecule poccess high reversibility under blue light or by heating,but still maintain well thermal stability at room temperature.HTP value varies dramatically as the photoisomeriztion goes on and the intensity of the red fluorescence is weakened by eight times.Besides,by doping 2B2TDCE,the reflection wavelength of the fluorescent CLCs can shift among the whole visible light region and they can be reversibly written/erased by blue/green light irradiation.