What is the difference between Rhodamine 123 and Rhodamine B?

Rhodamine 123

• Green fluorescent mitochondrial dye
• Molecular formula C₂₁H₁₇ClN₂O₃
• Excitation maxima 507 nm
• Emission maxima 534 nm
• Soluble in ethanol 1 mg/mL
• Is cell membrane permeant
• Stains mitochondria in living cells
• Widely used in flow cytometry studies involving mitochondrial membrane potential and bacteria. Also used in biochemistry to inhibit mitochondrion function.

Rhodamine B

• Bright red fluorescent xanthene dye
• Molecular formula C₂₈H₃₁ClN₂O₃    
• Excitation maxima 568 nm
• Emission maxima 583 nm
• Soluble in water and methanol
• Functions as a water tracer fluorescent
• Widely used as a fluorescent dye in confocal microscopy and for cross staining 1-N-methylamino-5-isocyanonaphthalene (MICAN)

Rhodamine B is used in biology as a staining fluorescent dye to demonstrate acid-fast organisms, notably mycobacterium. Rhodamine B is also a commonly used dye for industrial purposes such as printing and dyeing in textile, paper, paints, leathers, and so on.