The Excited State Intramolecular Proton Transfer (ESIPT) phenomenon involving photo-induced keto-enol tautomerization is known to cause significant variations in the excited state structures and photophysical properties of certain molecules. Here, the dual emission exhibited by 3,6-dihydroxybenzene-1,2,4,5-tetracarboxylic acid tetraethyl ester has been studied both experimentally and theoretically and it is concluded that the second emission is due to ESIPT in polar protic solvents, while it is due to dianion formation in solvents like DMSO and DMF.

中文翻译：

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对3,6-二羟基苯-1,2,4,5-四羧酸四乙酯的双重荧光的认识–实验和理论研究

已知涉及光诱导的酮-烯醇互变异构的激发态分子内质子转移（ESIPT）现象会引起某些分子的激发态结构和光物理性质的显着变化。在此，对3,6-二羟基苯-1,2,4,5-四羧酸四乙酯表现出的双重发射进行了实验和理论研究，得出的结论是第二次发射是由于极性质子溶剂中的ESIPT，而这是由于在DMSO和DMF等溶剂中形成了阴离子。