Study On The Synthesis Of Chalcone Derivatives And Their Photosensitive Characteristics

Photochemical reactions in organic materials induce changes in physic-chemical properties and may be applied in various photo-devices. Compared to cinnamoyl derivatives, chalcone compound has the advantages of good hydrolysis resistance, thermal stability and very high absorption coefficient around 300-365 nm which could be potentially used in the fields of lithography, printing, liquid crystalline display and nonlinear optics materials. As one of the most well-known and extensively studied classes of organic photochromic compound, spiropyran derivatives have the virtues of fast response speed, convenient regulation and easily obtained. But the poor stability and durability of merocyanine structure restricts the practical applications.In this paper, a series of copolymers and small molecules containing chalcone groups were prepared first, then the photocrosslinking properties and influencing factors were investigated. The photocycloaddition of chalcone moieties was applied to improve the stability of the colored species of photochromic spiropyran. By the means of a modified miniemulsion polymerization, the hydrophobic spiropyan and chalcone derivatives were polymerized into nanoparticles in aqueous dispersions, which would expand the application ranges of the photosensitive compounds. It has been found that:1) Based on the reaction properties of 3-isopropenyl-α,α′-dimethylbenzyl isocyanate (TMI), UV sensitive polymers comprising pendant chalcone groups were obtained by two synthetic routes. Under irradiation of UV light, the photoconversion of the chalcone group was low due to the rigid structure of copolymers. While samples containing soft spacer chain between chalcone group and polymer chain showed slow photocrosslinking rate and a relative high photocrosslinking content.2) Three MA-chalcone monomers with different spacers were synthesized and polymerized with acrylate comonomers. All photosensitive copolymers were easily soluble in polar solvents. The photocrosslinking properties were investigated in solutions and found that increasing the percent of comonomers, decreasing the length of spacer chain, adding the length of side chain of comonomers and reducing the concentration of polymers in solution will decrease the photocrosslinking rate of chalcone groups, and vise versa.3) A series of bis-chalcone compounds, bifunctional compounds of SP-CH and bifunctional copolymers with different Tg were synthesized and used to prepare UV sensitive films. Irradiated with 365 nm UV light, the photocrosslinking reaction between chalcone units and photochromism transformation of spiropyran in the films proceeded coincidently. As compared to films solely containing SP, the decolorization of spiropyran in films containing chalcone moieties was much retarded after UV irradiation. This was contributed to the increasing of steric hindrances of the polymer matrix by photocycloaddition of chalcone moieties. At the same time, the properties of polymer matrix also affected the photoreaction. When crosslinked at the temperature above Tg of the polymer, the spiropyran was better stabilized due to the easy photocrosslinking reaction between chalcone groups generated by the movability of the polymer chain.4) Three di-acrylate chalcone compounds with different spacers were designed and synthesized. Those compounds were successfully applied to prepare UV sensitive nanoparticles as second crosslinkable crosslinkers via a modified miniemulsion polymerization process. The prepared nanoparticles have an average particle size less than 80 nm and narrow size distribution. The crosslinker helped to form uniform nanoparticles and stabilized the MC structure of SP after photocrosslinking reaction. The MA-chalcones of 2) were also used to prepare photosensitive nanoparticles, while the stabilization effect is less than di-acrylate chalcones. The nanoparticles could be dispersed in water easily and expand the application scope of the two kinds of photosensitive compounds.5) The bis-chalcone compounds and polymers showed anisotropic photocrosslinking properties when irradiated with polarized ultraviolet light, which could give a potential application as LC-alignment materials.All the molecules and polymers containing chalcone moieties obtained in this paper are potentially photofunctional materials, which are very sensitive to UV light and stabilize the photochromic spiropyran effectively.