Six mitochondria/lysosomes self-targetable and viscosity-sensitive dyes (1a–1f) were developed via simple structure modification on cyanine-derived dyes. They all showed remarkable OFF–ON fluorescent response to viscosity in the near-infrared region (652–690 nm) and exhibited good linear relationship with solution viscosity. The transient absorption spectra were used to evaluate the excited-state lifetime of dye 1a in different viscosity environments. Furthermore, cellular imaging assays indicated that different derivatives (1a–1f) with the same chromophore core exhibited different organelle-targeting abilities. Among them, dyes 1a–1c could sense lysosomal viscosity fluctuations while dyes 1d–1f could be applied in mitochondrial viscosity detections.

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