Synthesis And Properties Of Near-Infrared Conjugated Polymers

Owing to its superior advantages in remote sensing operations,microinvasion,and biological window,Near-infrared(NIR)light has been widely used in sensing,imaging,and biotherapy fields.Among NIR light absorbing materials,photothermal agents which can convert NIR light into thermal energy are important for convenient and efficient use of NIR light.In various photothermal conversion reagents,D-A conjugated polymer is an ideal organic photothermal reagent.It is widely used because of its ability to achieve sharp NIR absorption peaks and spectral adjustability through D,A units,and has good light stability and good biocompatibility.Isoindigo and its derivatives have been developed as photothermal conversion reagents due to their good planarity.Therefore,we hope to further improve the photothermal conversion performance based on Isoindigo.In this paper,the outer benzene ring of BIBDF is replaced by pyridine ring and thiophene ring respectively to realize the design of high photothermal conversion material.The specific work is as follows.In the second chapter,we use the pyridine ring instead of the outer benzene ring of BIBDF,namely the aza-isoindole derivative(BABDF),which increases the electronwithdrawing ability of the acceptor,and then use thiophene(BT),benzodithiophenethiophene(BDTT),thiophene-vinylene-thiophene(TVT)as donors,three conjugated polymers were synthesized,namely PBABDF-BT,PBABDF-BDTT,PBABDF-TVT.The photothermal conversion efficiency of PBABDF-BT reached 32.4%,the photothermal conversion efficiency of PBABDF-BDTT was only 23.5%,and PBABDF-TVT showed excellent photothermal conversion efficiency of 40.7%.Through Gaussian simulation and corresponding mass extinction coefficient,PBABDF-TVT exhibits a more planar molecular structure and a higher mass extinction coefficient.It is indicated that while increasing the electron-withdrawing ability of the acceptor,prolonging the conjugate length of the donor unit in the main chain direction can effectively improve the photothermal conversion efficiency of the conjugated polymer.In Chapter 3,we replaced the outer benzene ring of BIBDF with a thiophene ring to reduce the band gap of the polymer.That is,the thiophene-isoindole derivative(BTPBF)is used as an acceptor,and the thiophene(BT)as a donor to synthesize the polymer PBTPBF-BT.The polymer was found to exhibit a broad UV absorption with a maximum absorption peak in the second infrared window(1072 nm)and an extremely narrow band gap(1.24 eV).Through the photothermal characterization of polymer nanoparticles,the photothermal conversion efficiency reaches 55.6%.Then we carried out photothermal characterization of the polymer film and found that the photothermal conversion efficiency is 51.3%,which is basically the same,indicating that the polymer has more excellent photothermal conversion ability.We further applied it to the cholesteric liquid crystal reflective device to realize the phase change of the photocontrolled liquid crystal and the reflection wavelength under the first infrared window and the second infrared window.