Eosin-5-isothiocyanate is a good photosensitizer and can be used to selectively label amines. 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.^1,2 Additionally, eosin is a good fluorescence acceptor for fluorescein (FAM), dansyl and coumarin dyes in fluorescence resonance energy transfer (FRET).

• l_ex\l_em(pH9) = 521/544 nm
• e = 95,000
• Orange red solid soluble in DMF or DMSO
• Store at -20?C and protect from light
• C₂₁H₇Br₄NO₅S
• Mwt: 704.96