Intracellular viscosity is closely related to a series of biological processes and could be a biomarker for various diseases. Herein, we reported a deep-red emission viscosity probe ACI, which showed a turn-on fluorescence effect with excellent selectivity encountering high viscous medium. To assure the practical biological application, ACI demonstrated not only a long wavelength emission at 634 nm but also a long wavelength excitation at 566 nm, which were crucial to afford deeper penetration depth and higher sensitivity in bioimaging. The photophysical properties and viscosity recognition mechanism of the probe were carefully discussed here. Theoretical calculations furtherly confirmed that high viscous medium could inhibit the twisted intramolecular charge transfer (TICT) process of the probe which quenched the fluorescence in low viscous media, and restore the emission. More importantly, it was successfully applied to visualize the viscosity in living cells.

细胞内粘度与一系列生物过程密切相关，并且可能是各种疾病的生物标记。在本文中，我们报道了一种深红色发射粘度探针ACI，它在高粘度介质中显示出具有优异选择性的开启荧光效果。为了确保实际的生物学应用，ACI不仅证明了在634 nm处的长波长发射，而且在566 nm处的长波长激发，这对于提供更深的穿透深度和更高的生物成像灵敏度至关重要。探针的光物理性质和粘度识别机理在此进行了仔细讨论。理论计算进一步证实，高粘度介质可以抑制探针的扭曲分子内电荷转移（TICT）过程，该过程可以在低粘度介质中猝灭荧光，并恢复发射。更重要的是，它已成功应用于可视化活细胞中的粘度。