Kaede is the prototype of the optical highlighter proteins, which are an important subclass of the fluorescent proteins that can be permanently switched from green to red emitting forms by UV irradiation. This transformation has important applications in bioimaging. Optimising brightness, i.e. enhancing fluorescence characteristics, in these proteins is an important objective. At room temperature, the excited state dynamics of the red form of the kaede chromophore are dominated by a broad distribution of conformers with distinct excited state kinetics. Here, we investigate substituent effects on the photophysics of this form of the kaede chromophore. While an electron withdrawing substituent (nitro) red shifts the electronic spectra, the modified chromophores showed no significant solvatochromism. The lack of solvatochromism suggests small changes in permanent dipole moment between ground and excited electronic states, which is consistent with quantum chemical calculations. Ultrafast fluorescence and transient absorption spectroscopy reveal correlations between radiative and nonradiative decay rates of different conformers in the chromophores. The most significant effect of the substituents is to modify the distribution of conformers. The results are discussed in the context of enhancing brightness of optical highlighter proteins.

中文翻译：

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取代基对 Kaede 发色团光物理学的影响


Kaede 是荧光荧光笔蛋白的原型，荧光荧光笔蛋白是荧光蛋白的重要亚类，可以通过紫外线照射从绿色发射形式永久转换为红色发射形式。这种转变在生物成像中具有重要的应用。优化这些蛋白质的亮度，即增强荧光特性是一个重要的目标。在室温下，Kaede 发色团的红色形式的激发态动力学由具有不同激发态动力学的广泛分布的构象异构体主导。在这里，我们研究了取代基对这种形式的 Kaede 发色团的光物理学的影响。虽然吸电子取代基 （nitro） 红使电子光谱发生偏移，但修饰的发色团没有显示出明显的溶剂变色。缺乏溶剂变色表明基态和激发电子态之间的永久偶极矩变化很小，这与量子化学计算一致。超快荧光和瞬态吸收光谱揭示了发色团中不同构象异构体的辐射和非辐射衰减速率之间的相关性。取代基最显着的作用是改变构象异构体的分布。在提高光学荧光笔蛋白亮度的背景下讨论了结果。