Matikonda Siddharth S, Hammersley Gabrielle, Kumari Nikita, Grabenhorst Lennart, Glembockyte Viktorija, Tinnefeld Philip, Ivanic Joseph, Levitus Marcia, Schnermann Martin J
Chemical Biology Laboratory, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 376 Boyles Street, Frederick, Maryland 21702, United States.
School of Molecular Sciences and The Biodesign Institute at Arizona State University, Tempe, Arizona 85287, United States.
J Org Chem. 2020 May 1;85(9):5907-5915. doi: 10.1021/acs.joc.0c00236. Epub 2020 Apr 10.
Appending conformationally restraining ring systems to the cyanine chromophore creates exceptionally bright fluorophores in the visible range. Here, we report the application of this strategy in the near-infrared range through the preparation of the first restrained heptamethine indocyanine. Time-resolved absorption spectroscopy and fluorescence correlation spectroscopy verify that, unlike the corresponding parent unrestrained variant, the restrained molecule is not subject to photoisomerization. Notably, however, the room-temperature emission efficiency and the fluorescence lifetime of the restrained cyanine are not extended relative to the parent cyanine, even in viscous solvents. Thus, in contrast to prior reports, the photoisomerization of heptamethine cyanines does not contribute significantly to the excited-state chemistry of these molecules. We also find that the fluorescence lifetime of the restrained heptamethine cyanine is temperature-insensitive and significantly extended at moderately elevated temperatures relative to the parent cyanine. Finally, computational studies have been used to evaluate the impact of the conformational restraint on atomic and orbital structure across the cyanine series. These studies clarify the role of photoisomerization in the heptamethine cyanine scaffold and demonstrate the dramatic effect of restraint on the temperature sensitivity of these dyes.
在花菁发色团上连接构象限制环系统可在可见光范围内产生异常明亮的荧光团。在此，我们通过制备首个受限七甲川吲哚菁报告了该策略在近红外范围内的应用。时间分辨吸收光谱和荧光相关光谱证实，与相应的母体非受限变体不同，受限分子不会发生光异构化。然而，值得注意的是，即使在粘性溶剂中，受限花菁的室温发射效率和荧光寿命相对于母体花菁也没有延长。因此，与先前的报道相反，七甲川花菁的光异构化对这些分子的激发态化学没有显著贡献。我们还发现，受限七甲川花菁的荧光寿命对温度不敏感，并且相对于母体花菁在适度升高的温度下显著延长。最后，已使用计算研究来评估构象限制对整个花菁系列原子和轨道结构的影响。这些研究阐明了光异构化在七甲川花菁支架中的作用，并证明了限制对这些染料温度敏感性的显著影响。
