Cell biology 

Eosin-5-maleimide is a good photosensitizer and can be used to selectively label thiols. It has a quantum yield of 0.57 for singlet oxygen generation, which makes it useful for photoconversion of electron-rich materials such as diaminobenzidine (DAB) or fluorescent dyes into highly electron-dense materials for high resolution electron microscopy studies. Additionally, eosin is a good fluorescence acceptor for fluorescein (FAM), dansyl and coumarin dyes in fluorescence resonance energy transfer (FRET).

• λ_Ex/λ_Em (MeOH) = 524/545 nm
• ε = 100,000
• Orange solid soluble in DMF or DMSO
• Store at -20°C and protect from light
• C₂₄H₉Br₄NO₇
• MW: 742.95