Systematic Modifications of a Simple Tolan: Another Category of Viscosity Sensor.

The first tolan derivative-based viscosity sensor (5d) has been synthesized, and its fluorescence intensity and lifetime increase when the viscosity of the solvent increases in methanol-glycerol mixtures. Phthalide (5d) was selected among structurally diverse tolan derivatives through systematic modifications of a simple tolan. To test 5d as a viscosity sensor, fluorescence lifetime imaging (FLIM) images of HeLa cells were obtained upon treatment with 5 μM of 5d to map the viscosity of the HeLa cells.