Water Induced Isomerization Of Light Sensitive DASAs And Its Application

Donor–acceptor Stenhouse adducts are a novel class of visible light-responsive negative photochromes,which was first synthesized and reported in 2014.Under visible light,the colored linear DASAs will undergo linear-to-cyclic isomerization,while the colorless cyclic DASAs will quickly change back to linear DASAs after heating.Due to a series of molecular property changes(such as color,size,polarity,etc.)caused by external light stimulation,DASAs has been widely studied and applied in the fields of photocontrolled drug release,photo-controlled supermolecular self-assembly and photoetching surface micrographics.The main content of this thesis includes the following three aspects:1.In this study,we first introduced DASAs onto the material surface through dopamine polymerization based on the polarization change of the photo-controlled molecules of DASAs,and further realized the photoinduced switching of surface wettability.The silica particles were then fixed on the substrate surface to prepare the optical wettability surface.Under the irradiation of green light,DASAs on the surface changes increases the surface hydrophilicity and changes the contact.On the other hand,heating causes cyclical-to-linear isomerization of DASAs molecules and increases the hydrophobicity of the surface.The process is reversible under the treatment of reciprocating green light-heating.Controlling wettability of material surface by visible light is helpful for future research in light sensitive tissue engineering and cell culture.2.During our study of light-controlled controlled surface wettability,we found that light is not the only external stimulus that can induce DASAs linear-to-cyclic isomerization.We discovered by chance that under the action of water,linear DASAs can slowly transform into cyclic DASAs without external light.We further studied the mechanism.Through density functional theory(DFT)calculations,we find that water molecules can bind to DASAs and generate cyclic DASAs·xH2O.Cyclic DASAs·xH2O is very stable at room temperature,but after heating it can quickly lose bound water molecules and transition back to linear DASAs.In addition,in the in-depth study and discussion of the isomerization process,we found that DASAs bound by water molecules showed a stepped decline of molecular free energy in the linear-to-cyclic isomerization process,which was helpful for the generation of cyclic DASAs.3.In addition,we prepared invisible ink through DASAs,and used ordinary pens and commercial inkjet printers to achieve the confidentiality of text,image and two-dimensional code information.Confidential information is not visible at room temperature and humidity,but can be quickly developed after heating.After the development of the information through high humidity treatment can be invisible again.Furthermore,by combining DASAs with oxazolidane(OXs),another water chromotropic molecule,we have achieved a leap from single to double secrecy in invisible ink.Different from the single confidential information can only change from "nothing" to "have",the double confidential information can switch back and forth between "false" and "true",which greatly improves the security of the confidential information.