叶绿素在经过加酸或加热或脱镁作用后会变成脱镁叶绿素（英语：Pheophytin，大陆也称为褐藻素）颜色也会改变。在水污染的地方，会造成浮游植物细胞破碎死亡时，其原本所含的叶绿素也跟着被破坏，而转变成脱镁叶绿素。因此脱镁叶绿素的含量比例可以作为水质的指标之一。

Pheophytin or phaeophytin (abbreviated Pheo) is a chemical compound that serves as the first electron carrier intermediate in the electron transfer pathway of photosystem II (PS II) in plants, and the photosynthetic reaction center (RC P870) found in purple bacteria. In both PS II and RC P870, light drives electrons from the reaction center through pheophytin, which then passes the electrons to a quinone (Q_A) in RC P870 and RC P680. The overall mechanisms, roles, and purposes of the pheophytin molecules in the two transport chains are analogous to each other.