A highly sensitive viscosity probe based on ferrocene-BODIPY dyads.

Two novel ferrocene-BODIPY molecules FcEB and FcB have been synthesized and characterized. An "interlock" packing mode was demonstrated in both FcEB and FcB by analysis of X-ray diffraction data. FcEB exhibits a molecular rotor property with a significant enhancement of quantum yield in viscous solvent. The result shows that the emission of FcEB increased dramatically as the viscosity of solution increased and also confirms that the structure-optical properties can be tuned by the structure design of molecule and introduction of different functional group. Our studies reveal that the system has great potential for developing viscosity probes in biological systems.