揭示两种不同极性溶剂对 4'-甲氧基-3-羟基黄酮荧光染料激发态分子内质子转移的影响。
Unraveling the effect of two different polar solvents on the excited-state intramolecular proton transfer of 4'-methoxy-3-hydroxyflavone fluorescent dye.
机构信息
School of Mechanical and Electrical Engineering, Henan Institute of Science and Technology, Xinxiang 453003, China.
School of Mechanical and Electrical Engineering, Henan Institute of Science and Technology, Xinxiang 453003, China.
出版信息
Spectrochim Acta A Mol Biomol Spectrosc. 2020 Jan 15;225:117487. doi: 10.1016/j.saa.2019.117487. Epub 2019 Aug 26.
The fluorescence properties of 4'-methoxy-3-hydroxyflavone (M3HF) dye in different solvents were investigated through experimental (Phys. Chem. Chem. Phys., 2018, 20, 7885) and theoretical (Org. Chem. Front., 2019, 6, 218) methods. However, the intermolecular hydrogen bonds between M3HF and solvents were ignored. In this work, we investigated the effect of methanol (MeOH) and N,N-dimethylformamide (DMF) solvents on the excited-state intramolecular proton transfer (ESIPT) of M3HF fluorescent dye. In excited state (S), the intramolecular hydrogen bonds are significantly strengthened, which can facilitate the ESIPT processes. The calculated absorption and fluorescence spectra agree well with the experimental date. The fluorescence spectra of M3HF and ESIPT tautomers (T) were found to be sensitive to the solvent polarity. Upon photo-excitation, the electron density of the M3HF molecular is redistributed, which can provide driving force for the ESIPT. The polar solvents MeOH (hydrogen bond donor) and DMF (hydrogen bond acceptor) can form different types of intermolecular hydrogen bonds with M3HF. The two different bonding modes of intermolecular hydrogen bonds are expected to weaken the intramolecular hydrogen bond of M3HF to varying degrees. The analysis of the potential energy curves indicate that the ESIPT processes of M3HF can be hindered by the intermolecular hydrogen bonds. The intermolecular hydrogen bond of M3HF-DMF complex is weaker than that of M3HF-MeOH complex, while the potential barrier of the ESIPT process in DMF solvent is higher than that of in the MeOH solvent. This is principally because, in DMF solvent, the hydroxyl group H atom of M3HF can be captured by the O atom of DMF and form OH bond with O atom in the intermediate process of ESIPT. There appears an energy barrier hopping point on the potential energy curve of M3HF in DMF solvent but does not appear in MeOH solvent.
4'-甲氧基-3-羟基黄酮（M3HF）染料在不同溶剂中的荧光性质通过实验（Phys. Chem. Chem. Phys.，2018，20，7885）和理论（Org. Chem. Front.，2019，6，218）方法进行了研究。然而，M3HF 与溶剂之间的分子间氢键被忽略了。在这项工作中，我们研究了甲醇（MeOH）和 N，N-二甲基甲酰胺（DMF）溶剂对 M3HF 荧光染料激发态分子内质子转移（ESIPT）的影响。在激发态（S）下，分子内氢键显著增强，这有利于 ESIPT 过程。计算得到的吸收和荧光光谱与实验数据吻合较好。发现 M3HF 和 ESIPT 互变异构体（T）的荧光光谱对溶剂极性敏感。光激发后，M3HF 分子的电子密度重新分布，为 ESIPT 提供驱动力。极性溶剂 MeOH（氢键供体）和 DMF（氢键受体）可以与 M3HF 形成不同类型的分子间氢键。两种不同的分子间氢键结合方式预计会在不同程度上削弱 M3HF 的分子内氢键。势能曲线的分析表明，M3HF 的 ESIPT 过程可能会受到分子间氢键的阻碍。M3HF-DMF 络合物的分子间氢键比 M3HF-MeOH 络合物的弱，而在 DMF 溶剂中 ESIPT 过程的势垒高于在 MeOH 溶剂中的势垒。这主要是因为在 DMF 溶剂中，M3HF 的羟基 H 原子可以被 DMF 的 O 原子捕获，并在 ESIPT 的中间过程中与中间产物中的 O 原子形成 OH 键。在 DMF 溶剂中 M3HF 的势能曲线出现了一个能垒跳跃点，但在 MeOH 溶剂中则没有。
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