4′,5′‐Diaminofluoresein (DAF) and 4′,5′‐bis(dimethylamino)fluorescein (BDMAF) have been synthesized and their pH‐dependent photophysical properties and protolytic equilibria investigated. Although the parent fluorescein exhibits decreased emission upon decreasing pH, DAF displayed quenched emission at all pH values; surprisingly, BDMAF exhibited strong fluorescence only at pH 3–6, with its emission almost completely quenched under strongly acidic, neutral, and basic conditions.

中文翻译：

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4'，5'-双（二甲基氨基）荧光素表现出与荧光素不同的pH依赖性发射行为

合成了4'，5'-二氨基荧光素（DAF）和4'，5'-双（二甲基氨基）荧光素（BDMAF），并研究了其pH依赖的光物理性质和蛋白水解平衡。尽管母体荧光素在降低pH值时显示出降低的发射，但DAF在所有pH值下均显示出猝灭的发射。出乎意料的是，BDMAF仅在pH值为3–6时才显示强荧光，并且其发射在强酸性，中性和碱性条件下几乎完全被淬灭。