| Fluorescence imaging plays an important role in the diagnosis and treatment of diseases.In particular,near-infrared fluorescence imaging has attracted attention due to the advantages of diminished tissue auto-fluorescence,deeper penetrating capacity,and minimal scattering.There are only two clinically approved the first Near-infrared(NIR-I,700-900 nm)fluorophores,methylene blue(MB)and indocyanine green(ICG),both of which are small molecules that are rapidly excreted.The second Near-infrared(NIR-II,900-1700 nm)has the advantages of lower photon scattering,stronger penetration,smaller tissue absorption and lower tissue fluorescence.Therefore,the development of ideal NIRII fluorescent materials has important theoretical significance and practical application value.In this paper,several D-A type conjugated polymer based on 2,5-Bis((5-thiophen-2-yl)methylene)-3,6-bis(2-octyldodecyl)-2,5-dihydropyrazine were designed and synthesized,and their NIR-II fluorescence / photoacoustic dual-mode imaging and photothermal conversion properties were investigated.The results were as follows:1.The poly(2,5-Bis((5-thiophen-2-yl)methylene)-3,6-bis(2-octyldodecyl)-2,5-dihydrop-yrazine)(SP)was designed and synthesized.It emits fluorescence in NIR-II and has good photoacoustic and photothermal conversion properties.The fluorescence quantum yield of NIR-II was 0.2%.The temperature of nanoparticles solution is as high as 44.5? with the concentration 100 ?g/m L,under the irradiation of 660 nm laser.In vivo fluorescence experiments show that SPN nanoparticles have long body circulation time,good stability and biocompatibility,and can achieve fluorescence/photoacoustic dual-mode imaging.2.Thiophene,3-methoxythiophene and 3,4-ethylenedioxythiophene were used as electron donors to design three new conjugated polymers,poly[2,5-Bis((5-thiophen-2-yl)methylene)-3,6-bis(2-octyldodecyl)-2,5-dihydropyrazine-alt-thiophen](P1),poly[2,5-Bis((5-thiophen-2-yl)methylene)-3,6-bis(2-octyldodecyl)-2,5-dihydropyrazine-alt-3-methoxythiophene](P2)and poly[2,5-Bis((5-thiophen-2-yl)methylene)-3,6-bis(2-octyldodecyl)-2,5-dihydropyrazine-alt-3,4-ethylenedioxythiophene](P3).The donating electron ability of donor and fluorescence quantum yield are gradually enhanced.The fluorescence quantum yield of the conjugated polymer nanoparticles P3 with 3,4-ethylenedioxythiophene as electron donor is up to 0.729%,which is 2.33-fold that of the conjugated polymer nanoparticles P1 with thiophene as electron donor and 3.64-fold that of the conjugated polymer nanoparticles SPN.It is verified that the enhanced electron donor ability of donor can effectively improve fluorescence quantum yield of the conjugated polymer in NIR-II region.The temperature of P1,P2,and P3 were 47.9?,47.8?,50.2?,respectively,under the irradiation of 660 nm laser.3.Two new conjugated polymers,poly[2,5-Bis((5-thiophen-2-yl)methylene)-3,6-bis(2-octyldodecyl)-2,5-dihydropyrazine-alt-3-hexyl thiophene] P4 and poly[2,5-Bis((5-thiophen-2-yl)methylene)-3,6-bis(2-octyldodecyl)-2,5-dihydropyrazine-alt-3-(2-ethylhexyl)thiophene] P5,were designed using 3-hexyl thiophene and 3-(2-ethylhexyl)thiophene as electron donors.The two conjugated polymer donors twisted the polymer skeleton to different degrees,increased the steric hindrance,effectively weakened the fluorescence quenching caused by the accumulation state of the polymer,and thus increased the fluorescence quantum yield.Among them,the fluorescence quantum yield of conjugated polymer nanoparticles P5 using 3-(2-ethylhexyl)thiophene as electron donor is 1.12-fold that of nanoparticles P1 and 1.75-fold that of nanoparticles SPN.It is proved that the proposed enhancement of the steric hindrance of polymers can effectively improve the fluorescence quantum yield of conjugated polymers in NIR-II region.Conjugated polymer nanoparticles P4 and P5 also have good photothermal conversion efficiency.Under the irradiation of 660 nm laser,the temperature of nanoparticles aqueous solution is over 40?. |
PDF Full Text Request