Preparation And Photoisomerization Behaviors Of Dinaphthalene Azobenzene Cylic Molecules

The photoresponsive cholesteric liquid crystals?CLCs?can regulate the reflection wavelength upon light irradiation,thus changing the reflection colors of devices.The non-contact regulation mode has been widely used in fields of filters,information storages and displays.At present,most studies on the photosensitive CLCs focus on the synthesis of photosensitive chiral molecules with large helical twisting power ??? and its variation value of ?????,expanding the wavelength regulation range,and broadening application,etc.However,the relationship between the ? and ?? values and the structure of photosensitive molecules is still unclear,moreover,the kinetics of photosensitive chiral molecules during the photoisomerization process has been rarely studied.In recent years,scientists have found that chiral azobenzene molecules with cyclic structures have large degree of isomerization due to the limitation of ring tension and molecular rigidity on their conformation.In this paper,a series of different sizes of binaphthyl azobenzene molecules have been designed and synthesized successfully.The relationship between the ?/?? values and molecular structure,as well as the compatibility between molecular structures and nematic liquid crystals?NLCs?were explored through experimentation and theoretical calculations.The specific research contents are as follows:1)Three kinds of binaphthyl azobenzene cyclic molecules?R1-R3?with different alkane-oxygen chain lengths have been designed and synthesized in this paper.¹H-NMR spectra,¹³C-NMR spectra and infrared spectrum were used to characterize their structures.DFT was used to calculate the theoretical molecule structutres and the value of dihedral angle???,and UV-vis absorption spectrum and CD spectrum were used to study the chiral optical properties of chiral molecules.The results show that the length of the flexible chain in the cyclic structure has a significant effect on the molecular conformation and photoisomerization behavior.2)Photosensitive CLCs devices were prepared by using chiral dopants R1-R3.The?and??values of three chiral molecules in CLCs were investigated by POM combined with Cano-wedge cell method,and the photoisomerization kinetics upon different irradiation conditions,as well as the miscibility between dopants and NLC by calculating Teas solubility parameter.The results show that the?value is related to the?value of the molecular structure,and the??value is related to the degree of photoisomerization of the dopant molecule.At the same time,the miscibility between the dopant molecule and liquid crystal molecule also affects the values of ? and ??,the theoretical Teas solubility parameter shows that the miscibility between the dopants and NLCs increases with increasing of the length of alkoxane chain from R1 to R3.In addition,with the increasing of the length of alkoxane chain length,the photoisomerization rate constants of dopants increases for trans-cis transformation upon UV irradiation and decreases for the reverse process upon visible light irradiation either in isotropic acetonitrile or in anisotropic LCs,which is consistent with the change of the photoisomerization rate in the isotropic solvent.3)Prepared and studied a CLC devices with dopant R2,and the relationship between transmittance and reflection wavelength under different light irradiation time was investigated.The results enable the precise tuning of the pitch and selective reflection wavelength/color of CLCs.4)To improve the miscibility between dopant and NLC,based on the molecular structure of dopant R2,a new dinaphthalene azobenzene cyclic molecule R5 has been designed and prepared by introducing a group similar to the structure of LC host at the 6,6'site of the dinaphthalene union.¹H-NMR spectra and ¹³C-NMR spectra were used to characterized their structures.DFT was used to calculate the theoretical molecule structures,and UV-Vis absorption spectrum and CD spectrum were used to study the chiral optical properties of R5 molecule.The photoisomerization in CLCs has been investigated by POM combined with Cano-wedge cell method.In addition,the miscibility between the dopant and the LC host has been investigated by calculating Teas solubility parameters.Compared to the dopant R2,dopant R5 has higher ? value and a good miscibility with the LC host.