5-(and-6)-carboxy-2',7'-dichlorofluorescein is similar to carboxyfluorescein, but has lower pKa. It is useful for detecting pH in more acidic environment. Also see the membrane-permeant compound dichlorofluorescein diacetate.    pKa = 4.8  &lamba;Ex/&lamba;Em = 504/529 nm  ε= 90,000  Orange solid soluble in DMSO and pH>6 buffers  Store at room temperature and protect from light, especially in solution  C21H10Cl2O7  MW: 445  [111843-78-8]