“…In a low-viscosity environment, the probe releases weak fluorescence resulting from the free rotation of rotor-connected single or double bonds, while as viscosity increases their rotation was inhibited by forming a large conjugated system, and result in strong fluorescence in a tall-viscosity environment. , Interestingly, most rhodamine and other fluorophores-based viscosity probes, their rotors are composed of aromatic ring: benzo-indole, polyaniline group, benzo-thiophene, pyridine salt, quinoline, imidazole, azobenzene, etc. (Table S1 in the Supporting Information), ,− which have relatively a greater size and clumsy structures. As reported, the design principles of viscosity response probes include computed tomography (CT), 6 , aggregation-induced emission (AIE), , photoinduced electron transfer (PET), intramolecular charge transfer (TICT), and fluorescence resonance energy transfer (FRET). , Particularly, TICT is a good strategy for designing viscosity probes, as it can enhance fluorescence emissions through the restriction of intramolecular rotations. , Therefore, designing a NIR small molecule with great properties and TICT mechanism to detect changes in intracellular viscosity is of great importance.…”