Multistage dissociation of fluoroscein dyes, widely used in biological labeling, yields a variety of ionic and tautomeric forms in a wide range of pH values. In contrast to well-studied absorption spectra, the emission spectra are not quite readily interpreted due to their strong overlapping and proton transfer in electronically excited states. The least studied are the fluorescent properties of eosin and erythrosin dyes containing heavy atoms (Br, I), in which the characteristics of the dianionic form only are reliably determined. In the framework of the density functional theory using the B3LYP-functional including nonequilibrium solvation, the geometries of the series of ionic forms of eosin and erythrosin in the ground and excited states are found, and the electronic spectra are calculated. Based on the identified linear regression of the calculated and experimental data for the earlier resolved electronic spectra, for the first time, the emission spectrum maxima of the monoanionic, neutral quinoid, and cationic forms of the dyes are determined. The spectral peculiarities (Stokes shifts) are discussed in terms of variation of the molecule and ion geometries in the ground and excited states.

中文翻译：

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曙红和赤藓红的离子形式的电子光谱建模

广泛用于生物标记的荧光素染料的多级解离在很宽的 pH 值范围内产生各种离子和互变异构形式。与经过充分研究的吸收光谱相比，发射光谱由于它们在电子激发态的强烈重叠和质子转移而不太容易解释。研究最少的是含有重原子 (Br, I) 的曙红和赤藓红染料的荧光特性，其中仅可靠地确定了双阴离子形式的特征。在使用 B3LYP 泛函（包括非平衡溶剂化）的密度泛函理论的框架中，发现了基态和激发态中曙红和赤藓红的一系列离子形式的几何结构，并计算了电子光谱。基于较早解析的电子光谱的计算和实验数据的识别线性回归，首次确定了染料的单阴离子、中性醌型和阳离子形式的发射光谱最大值。光谱特性（斯托克斯位移）是根据分子和离子几何形状在基态和激发态的变化来讨论的。