Tetramethoxy-Aminorhodamine (TMARh): A Bichromophore, an Improved Fluorophore, and a pH Switch

Rhodamine is one of the most widely used fluorescent dyes. Here, a new synthetic pathway to the popular dyes is reported and the effect of adding four methoxy groups to the molecular structure is investigated. Tetramethoxy‐aminorhodamine (TMARh) is found to show superior pH switching compared to the rhodamine without the four methoxy groups, owing to changed properties of the dark “off” state and increased fluorescence intensity in the protonated “on” state. A new route to rhodamines is reported, resulting in tetramethoxy‐rhodamines with improved photophysical properties. It was found that tetramethoxy‐aminorhodamine is a bichromophore and a very efficient pH‐responsive dye.