荧光聚类肽的合成、自组装与聚集诱导发光效应

Synthesis,Self-Assembly and Aggregation-Induced Emission of Fluorescent Polypeptoids

采用1-(4-氨基苯)-1,2,2-三苯基乙烯(TPE-NH2)引发N-丁基甘氨酸-N-硫代羧酸酐(NBG-NTA)和N-乙基甘氨酸-N-硫代羧酸酐(NEG-NTA)开环聚合,制备了四苯基乙烯(TPE)基团封端的聚(N-丁基甘氨酸)-b-聚(N-乙基甘氨酸)(TPE-PNBG-b-PNEG)。采用透射电子显微镜(TEM)和荧光光谱(FL)研究了TPE-PNBG-b-PNEG在水溶液中的自组装行为和聚集诱导发光(AIE)特性。结果表明,TPE-PNBG-b-PNEG具有显著的AIE效应,根据初始含水量(体积分数)和亲水链段质量分数(wPNEG)的不同,TPE-PNBG-b-PNEG在水溶液中分别组装得到了球形胶束以及纺锤状、松针状和蠕虫状聚集体,并可发出强烈的蓝色荧光,最大发射波长为485 nm。随着wPNEG的减小,TPE-PNBG-b-PNEG的堆积参数增大,疏水链段的堆积变得更为紧密,AIE效应增强,其荧光强度和荧光量子产率都随之增强。

Tetraphenyl ethylene(TPE)-capped block copolypeptoid poly(N-butylglycine)-b-poly(N-ethylglycine)(TPEPNBG-b-PNEG)was synthesized through the 1-(4-aminophenyl)-1,2,2-triphenylethene(TPE-NH_(2))-initiated ring opening polymerization of N-butylglycine N-thiocarboxyanhydride(NBG-NTA)and N-ethylglycine N-thiocarboxyanhydride(NEGNTA).Three copolypeptoids with different mass ratios of hydrophilic PNEG block(wPNEG),TPE-PNBG10-b-PNEG41(wPNEG=70%),TPE-PNBG38-b-PNEG44(wPNEG=45%)and TPE-PNBG53-b-PNEG36(wPNEG=33%),were prepared by changing the feed molar ratios of monomer to initiator,whose compositions were confirmed by the proton nuclear magnetic resonance(1HNMR).Size exclusion chromatography(SEC)traces of the three copolypeptoids were all unimodal with narrow molecular mass distributions(Đ<1.30).The ultraviolet-visible(UV-Vis)absorption spectra exhibited that TPE-PNBG-b-PNEG had a strong absorption at 316 nm,which was corresponding to the characteristic absorption of TPE group.TPE-PNBG-b-PNEG showed distinct aggregation-induced emission(AIE)property by adding water to its N,N-dimethylformamide(DMF)solution,which was caused by the assembly of hydrophobic TPE groups and PNBG segments in DMF-H_(2)O system.When the initial water content(volume fraction)was 33%,TPE-PNBG53-b-PNEG36 assembled to spindle-like aggregates with an average length of 550 nm and width of 160 nm.When the initial water content was increased to 67%,TPE-PNBG53-b-PNEG36 assembled to worm-like aggregates with an average length of 650 nm and width of 90 nm.The higher initial water content would lead to the more tightly packed assemblies.With the increasing of wPNEG,TPE-PNBG38-b-PNEG44 assembled to pine leaf-like aggregates with an average length of 300 nm,while TPE-PNBG10-b-PNEG41 assembled to spherical micelles with a diameter around 50 nm.Under the excitation of 335 nm UV light,the assembly solution of the three copolypeptoids could emit strong blue light,with a maximum emission wavelength of 485 nm.The fluorescence intensity and fluorescence quantum yield of the assembly solution increased with the decreasing of wPNEG.As wPNEG gradually decreased,the packing parameters of TPE-PNBG-b-PNEG gradually increased,which led to the more compacted packing of the hydrophobic segments and subsequently enhanced the fluorescence intensity and fluorescence quantum yield due to the stronger AIE effect.