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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Tuning the emission properties of fluorescent ligands by changing pH: The unusual case of an acridine-containing polyamine macrocycle
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Tuning the emission properties of fluorescent ligands by changing pH: The unusual case of an acridine-containing polyamine macrocycle

机译：通过改变pH值来调节荧光配体的发射特性：含a啶的多胺大环化合物的不寻常情况

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摘要

Synthesis and characterization of a new macrocyclic compound, composed by a triethylentetraamine chain linking the 4 and 5 positions of an acridine moiety, are reported. The molecule, devised as a fluorescent chemosensor for anions, has revealed an intriguing pH-dependent spectroscopic behavior, whose features are the specific object of this article. Ligand protonation in aqueous solution has been analyzed by means of potentiometric, 1H NMR, UV-vis, and fluorescence emission measurements. The molecule binds up to four protons in the pH range 2-11. Protonation takes place on the aliphatic tetraamine chain, while the acridine nitrogen does not participate to proton binding even at very low pH. Differently from acridine, the UV-vis spectra are almost unaffected by the pH. On the opposite, the emission spectra are strongly pH-dependent. In fact, at low pH values, the spectra show a blue-shifted emission, resembling that of unprotonated acridine, while at slightly acidic and alkaline pH the fluorescence features a red-shifted band similar to that of acridinium cation. This unusual behavior occurs in the mono-, bi-, and triprotonated forms of the compound and is interpreted as due to an excited state proton transfer from an aliphatic ammonium group adjacent to the acridine moiety to the acridine nitrogen. In the fully protonated state, this process is prevented owing to unfavorable molecular arrangements mainly determined by electrostatic repulsions. This interpretation is supported by quantum mechanical calculations as well as molecular dynamics simulations.
机译：报道了一种新的大环化合物的合成和表征，该化合物由连接ethyl啶部分的4和5位的三亚乙基四胺链组成。该分子被设计为阴离子的荧光化学传感器，它揭示了一种有趣的pH依赖性光谱行为，其特征是本文的特定目标。水溶液中的配体质子化已通过电位分析，1 H NMR，UV-vis和荧光发射测量进行了分析。该分子在2-11的pH范围内最多可结合四个质子。质子化作用发生在脂肪族四胺链上，而a啶氮即使在非常低的pH值下也不会参与质子结合。与a啶不同，UV-vis光谱几乎不受pH的影响。相反，发射光谱强烈依赖于pH。实际上，在低pH值下，光谱显示蓝移发射，类似于未质子化a啶的发射，而在弱酸性和碱性pH下，荧光具有类似于a啶阳离子的红移带。这种不寻常的行为以化合物的单，双和三级磺酸化形式发生，并且可以解释为由于激发态质子从邻近the啶部分的脂族铵基团转移到a啶氮。在完全质子化的状态下，由于主要由静电排斥决定的不利的分子排列，防止了该过程。量子力学计算和分子动力学模拟都支持这种解释。

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