研究了不同温度、浓度、pH值条件下,不同代数、不同端基类型(酯端基和胺端基)的PAMAM(聚酰胺-胺)树形分子的强荧光发射性能.PAMAM树形分子发射强荧光是沿树形结构方向的酰胺基团中的n→π~*跃迁和其密实的球状结构共同作用的结果.树形分子的荧光强度在低pH值或者低温条件下大幅度提高,并且在稀溶液中与浓度成线性关系,在高浓度或者高代数条件下逐渐偏离线性关系.本文还对上述规律的内在机理进行了研究:第一,低pH值条件下,PAMAM树形分子内的叔胺基被氢离子质子化,酰胺荧光发射中心和叔胺基团之间的光诱导电子转移作用被抑制,甚至中断,因此荧光强度急剧升高;第二,随着温度升高,PAMAM树形分子的去活作用增强,荧光强度降低;第三,浓度超过临界点浓度后,由于浓度消光作用,PAMAM树形分子的荧光强度不再随浓度增加而线性增强.最后,将PAMAM树形分子水溶液用于锡纸上油印潜指纹的识别,经处理后的指纹在365 nm紫外光的激发下发射出蓝色荧光,潜指纹被成功地清晰识别.
A strong fluorescence emission from poly(amido amine) (PAMAM) dendrimers with different terminal groups(amine-terminated and carboxylate-terminated) was studied under different conditions by varing experimental parameters such as temperature, concentration and pH value. The intrinsic fluorescence of PAMAM dendrimer is due to an n→π~* transition from the amido groups throughout the dendritic structure and the close spherical structure of PAMAM. The fluorescence intensity increased fast at lower pH or lower temperature, linear with respect to dendrimer concentration when the dendrimer solution is dilute but depart from the linear relationship at higher concentration and higher dendrimer generations. The mechanism was studied carefully. First, it was reasonable that photoinduced electron transfer (PET) between fluorescence-emitting moiety and tertiary amine groups was prevented, or even eliminated when tertiary amine groups were protonated with H+ protons at lower pH, thus fluorescence intensity increased sharply accordingly. Also, the deactivation of luminescence was raised with increasing temperature. Further more, a critical concentration existed over which fluorescence intensity did not increased with linear relationship with increasing concentration because of concentration extinction effects. Oil latent fingerprints deposited on tinfoil surface treated with dendrimer solution emitted blue photoluminescence under ultraviolet excitation of 365 nm from an UV LED in the dark. Fingerprint was successfully detected with good resolving rate.
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