Figure 4.

Exploiting the environmental sensitivity of SiR-CO₂H to increase apparent photostability. a) SiR-CO₂H equilibrates between two forms, a closed, lactone form that is dark, and an open form that is bright. The position of this equilibrium depends on both pH and the polarity of the environment. b) Appending the SiR chromophore to a protein in an aqueous environment shifts this equilibrium towards the open, bright form, while appending it to a lipid in a membrane environment shifts the equilibrium towards the closed, dark form.