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.