Syntheses and properties of the V-shaped dimeric xanthene dyes.

Two new types of V-shaped dimeric xanthene fluorescent dyes were synthesized and evaluated in terms of their optical properties. Based on differences in their resonance forms, these V-shaped dyes were able to adopt four different protonation states (i.e., cationic, neutral, monoanionic and dianionic states) depending on their external environment. Notably, these compounds allowed for the bright fluorescent imaging of NIH3T3 cells when they were applied to cells as the corresponding diacetylated materials.