Fluorescence and photoinduced proton transfer in the protolytic forms of fluorescein: Experimental and computational study
Fluorescence and photoinduced proton transfer in the protolytic forms of fluorescein: Experimental and computational study
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DOI：
10.1016/j.dyepig.2019.107851
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发表时间：
2020-02-01
影响因子：
4.5
通讯作者：
Slyusareva, Evgenia A.
中科院分区：
文献类型：
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作者：
Gerasimova, Marina A.;Tomilin, Felix N.;Slyusareva, Evgenia A.
与已研究过的不同质子型荧光素的吸收光谱相比，由于电子激发态发射和光诱导质子转移之间的相互作用，人们对宽pH范围内荧光光谱的复杂结构并不完全了解。我们通过对实验数据的联合分析，在pH 0.3-10.5的吸收和稳态荧光光谱获得的数据，以及含时间的密度泛函理论(TD-DFT)，对这种相互作用提供了洞察力。基于TD-DFT的计算模型在二阴离子上得到了验证，并用于模拟其他质子酸形式的光谱。根据三个发色团环上的部分电荷对荧光素的质子裂解/互变异构形式进行了分类，并根据分子几何和轨道的变化分析了电子跃迁。基于吸收峰和已知的双阴、阳离子荧光峰的计算结果与实验结果之间的线性回归分析被用来指定单阴离子(496 Nm)、中性奎宁(550 Nm)和中性两性离子(483 Nm)的荧光峰，其位置在本工作之前是不清楚的。利用Forster循环，结合光谱测量和计算数据，计算了不同形式荧光素的激发态解离微常数值pK(A)*。
In contrast to the well-studied absorption spectra of different protolytic forms of fluorescein, the complex structure of the fluorescence spectra in a wide pH range is not completely understood because of the interplay between emission and photoinduced proton transfer in the electronic excited states. We provide insight into this interplay through a combined analysis of the experimental data, obtained by absorption and steady-state fluorescence spectroscopy at pH 0.3-10.5, and the time-dependent density functional theory (TD-DFT). The TD-DFT based computational model is validated on dianion and used to model the spectra of other protolytic forms. The protolytic/tautomeric forms of fluorescein are classified according to the partial charges on the triple chromophore ring, and electronic transitions are analyzed in terms of changes in molecular geometries and orbitals. A linear regression analysis between the calculated and experimental results based on both absorption and well-understood dianionic and cationic fluorescence peaks is used to assign the monoanionic (496 nm), neutral quinoid (550 nm) and neutral zwitterionic (483 nm) fluorescence peaks, whose positions were not clear prior to this work. The values of the excited-state dissociation microconstants pk(a)*for different forms of fluorescein are calculated by means of the Forster cycle in conjunction with the spectroscopic measurements and computational data.