Dual-mode tunable viscosity sensitivity of a rotor-based fluorescent dye

The design and fabrication of new type viscosity sensor on molecular scale will enrich the detection means in both physical and life sciences. In this work, a rotor-containing fluorescent dye was prepared, which can reveal a typical viscosity-sensitive behavior due to the environment-induced non-radiative decay. The viscosity-sensitive behavior of this dye could be tunable (locked and activated) in aqueous environment, either with the reversible light-driven trans/cis-photoisomerization of the cyanostilbene moiety, or with the reversible assembly/disassembly process of β-cyclodextrin (β-CD) to the rotor part. Such dual-mode tunable viscosity sensitivity can be well distinguished by fluorescent spectra. A slope method, on double-logarithmic plots of the fluorescent signal to the corresponding environmental viscosity, makes a quantitative estimation to the tunable viscosity sensitivity, featuring the 'Activated' and the 'Locked' state in this molecular-scale viscometer.