Study On The Relationship Between The Photoresponsive Properties Of DASAs And Their Structure

Donor-acceptor Stenhouse adducts(DASAs)were first proposed as novel photochromic molecules in 2014.This class of molecules has two isomers: hydrophobic colored linear isomers and hydrophilic colorless cyclic isomers.Under visible light,linear DASAs with a triene structure will undergo a series of molecular bond rotation and molecular bond formation steps to isomerize to cyclic DASAs;and in the dark or heated environment,cyclic DASAs will revert to linear DASAs.The reciprocating transition of DASAs between linear and cyclic has brought about significant controllable changes in molecular structure and properties,including molecular size,molecular polarity,molecular spectrum,etc.As a result,DASAs have been widely studied and applied in the fields of light-controlled supramolecular self-assembly,surface functionality,and biomedicine.Similar to traditional light-sensitive molecules,the photoisomerization properties of DASAs are closely related to their molecular structure.And mastering the method of controlling the light sensitivity of DASAs by adjusting the molecular structure is also of great significance for the application and development of DASAs.Based on this,this article studies the relationship between the light-sensitive properties of DASAs and their molecular structure.This article is mainly composed of the following three aspects:1.To study the effect of changing the molecular structure of electron acceptor/donor on the photoresponsive properties of DASAs.By controlling the electron donor part(dipropylamine)unchanged,1,3-dimethylbarbituric acid,Meldrum’s acid and 1,3-indandione were used as electron acceptors to study the absorption spectra and isoforms of DASAs.At the same time,we also studied the influence of the molecular structure of different electron donors on the isomerization properties of DASAs by controlling the electron acceptor part.We found that,compared with the electron donor part,the photoisomerization properties of DASAs can be changed more obviously by changing the molecular structure of the electron acceptor part.Although the molecular structure of the electron donor is quite different,it has little effect on the isomerization properties.2.Based on the above research,we believe that the relative position of the benzene and the triene structure of the electron donor part may be a direct factor affecting the photoisomerization properties of DASAs.In order to prove this conjecture,we fine-tuned the donor structure of DASAs by changing the length of the carbon chain spacer between the benzene and the N-methyl group at the donor site,and studied the effects of different carbon chain spacer lengths on the photoresponsive properties of DASAs.The influence was explained by density functional theory(DFT)calculations,and a strategy was proposed to control the light sensitivity of DASAs molecules by adjusting the relative position of the electron donor part of the benzene and the triene structure.We found that the shorter the carbon chain length of DASAs,the faster the photoisomerization rate,while the thermal isomerization rate is just the opposite.This also shows that the relative position between the benzene and the triene structure is the key to the photoisomerization properties of DASAs,which confirms our conjecture.3.After completing the study of controlling the photoisomerization properties of DASAs by adjusting the molecular structure of the electron donor and electron acceptor,we tried to modify the triene structure to achieve a new control scheme for the photoisomerization properties of DASAs.In the process of research,we accidentally discovered a new type of structure similar to DASAs and also light-sensitive.This is of great significance to the development of light-sensitive materials.