The excited state intramolecular proton transfer (ESIPT) of 3-hydroxyflavone derivatives results in a fluorescence spectrum composed of two emission bands, the relative intensity of which is strongly influenced by the interaction with the local environment. We use time-resolved fluorescence and ultrafast transient absorption spectroscopies to investigate the photophysics of 4′-methoxy-3-hydroxyflavone in different solvents characterized by various polarities and hydrogen (H) bonding capabilities. We evidence that in this compound, the ESIPT reaction rate varies by more than 3 orders of magnitude, depending on the H-bonding capability of its local environment. This remarkable property is attributed to the moderate electron-donating strength of the 4′-methoxy substituent, and turns this fluorescent dye into a very promising fluorescent probe of biomolecular structures and interactions, where local structural heterogeneity may possibly be revealed by resolving a distribution of ESIPT reaction rates.

中文翻译：

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对环境敏感的4'-甲氧基-3-羟基黄酮荧光染料的超快光物理性能†

3-羟基黄酮衍生物的激发态分子内质子转移（ESIPT）导致荧光光谱由两个发射带组成，其相对强度受与本地环境的相互作用的强烈影响。我们使用时间分辨荧光和超快瞬态吸收光谱研究了4'-甲氧基-3-羟基黄酮在不同溶剂中的光物理特性，这些溶剂具有不同的极性和氢（H）键结合能力。我们证明，在该化合物中，ESIPT反应速率的变化幅度超过3个数量级，这取决于其局部环境的H键结合能力。这种非凡的特性归因于4'-甲氧基取代基的中等供电子强度，