Center for Biomedical Photonics, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
Molecules. 2020 Jan 29;25(3):585. doi: 10.3390/molecules25030585.
Two probes, AIE-1 and AIE-2, were synthesized to investigate the effect of substitutional functional group on aggregation (aggregation-caused quenching (ACQ) or aggregation-induced emission (AIE)) and intramolecular charge transfer (ICT) behavior as well as on the cell imaging aspect. The yellow-color non-substituted probe AIE-1 showed weak charge-transfer absorption and an emission band at 377 nm and 432 nm, whereas the yellowish-orange color substituted probe AIE-2 showed a strong charge-transfer absorption and an emission band at 424 nm and 477 nm in THF solvent. The UV-Vis studies of AIE-1 and AIE-2 in THF and THF with different water fractions showed huge absorption changes in AIE-2 with high water fractions due to its strong aggregation behavior, but no such noticeable absorption changes were observed for AIE-1. Interestingly, the fluorescence intensity of AIE-1 at 432 nm gradually decreased with increasing water fractions and became almost non-emissive at 90% water. However, the monomer-type emission of AIE-2 at 477 nm was shifted to 584 nm with a 6-fold increase in fluorescence intensity in THF-HO (1:9, ) solvent mixtures due to the restriction of intramolecular rotation on aggregation in high water fractions. This result indicates that the probe AIE-1 shows ACQ and probe AIE-2 shows AIE behaviors in THF-HO solvent mixtures. Furthermore, the emission spectra of AIE-1 and AIE-2 were carried out in different solvent and with different concentrations to see the solvent- or concentration-dependent aggregation behavior. Scanning electron microscope (SEM) and dynamic light scattering (DLS) experiments were also conducted to assess the morphology and particle size of two probes before and after aggregation. Both of the probes, AIE-1 and AIE-2, showed less toxicity on HeLa cells and were suitable for cell imaging studies. Density functional theory (DFT) calculation was also carried out to confirm the ICT process from an electron-rich indole moiety to an electron-deficient cyano-phenyl ring of AIE-1 or AIE-2.
合成了两个探针 AIE-1 和 AIE-2，以研究取代官能团对聚集（聚集猝灭（ACQ）或聚集诱导发射（AIE））和分子内电荷转移（ICT）行为以及细胞成像方面的影响。黄色非取代探针 AIE-1 显示出弱的电荷转移吸收和在 377nm 和 432nm 处的发射带，而黄色橙色颜色取代探针 AIE-2 在 THF 溶剂中显示出强的电荷转移吸收和在 424nm 和 477nm 处的发射带。在 THF 和不同水分数的 THF 中，AIE-1 和 AIE-2 的紫外-可见研究表明，由于其强聚集行为，AIE-2 在高水分数下显示出巨大的吸收变化，但在 AIE-1 中没有观察到这种明显的吸收变化。有趣的是，AIE-1 在 432nm 处的荧光强度随着水分数的增加逐渐降低，在 90%水时几乎不发射。然而，AIE-2 的单体型发射在 477nm 处转移到 584nm，荧光强度增加了 6 倍，这是由于在高水分数下聚集时分子内旋转受到限制。这一结果表明，探针 AIE-1 在 THF-HO 溶剂混合物中表现出 ACQ 行为，而探针 AIE-2 表现出 AIE 行为。此外，还在不同溶剂和不同浓度下进行了 AIE-1 和 AIE-2 的发射光谱研究，以观察溶剂或浓度依赖性聚集行为。还进行了扫描电子显微镜（SEM）和动态光散射（DLS）实验，以评估两种探针在聚集前后的形态和粒径。探针 AIE-1 和 AIE-2 对 HeLa 细胞的毒性较小，适合细胞成像研究。还进行了密度泛函理论（DFT）计算，以确认从富电子吲哚部分到 AIE-1 或 AIE-2 的缺电子氰基苯基环的 ICT 过程。
