In crystals, adjacent Fe2+ and Ti4+ have a characteristic effect on this property. Heating alkali metal halides unusually changes this property by forming F-centers. A change in this property is produced by an equilibrium between a ring opening and closing at the oxygen of a sultone (15[1])or lactone in many triarylmethane compounds. Point defects in lattices that change this property are called this property’s namesake (*) centers. In many compounds, this property is caused by charge-transfer bands. Electronic transitions between d orbitals confer this property to many coordination complexes (-5[1])of transition metals. A change in this property at the equivalence point marks the end of acid-base titration. For 10 points, name this property used to show the pH of a solution by indicators such as phenolphthalein. (10[1])■END■