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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Origin of the Absorption Band of Bromophenol Blue in Acidic and Basic pH: Insight from a Combined Molecular Dynamics and TD-DFT/MM Study
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Origin of the Absorption Band of Bromophenol Blue in Acidic and Basic pH: Insight from a Combined Molecular Dynamics and TD-DFT/MM Study

机译：酸性和碱性pH下溴酚蓝吸收带的起源：结合分子动力学和TD-DFT / MM研究的见解

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摘要

We study the linear and nonlinear optical properties of a well-known acid base indicator, bromophenol blue (BPB), in aqueous solution by employing static and integrated approaches. In the static approach, optical properties have been calculated using time-dependent density functional theory (TD-DFT) on the fully relaxed geometries of the neutral and different unprotonated forms of BPB. Moreover, both closed and open forms of BPB were considered. In the integrated approach, the optical properties have been computed over many snapshots extracted from molecular dynamics simulation using a hybrid time-dependent density functional theory/molecular mechanics approach. The static approach suggests closed neutral double right arrow anionic interconversion as the dominant mechanism for the red shift in the absorption spectra of BPB due to a change from acidic to basic pH. It is found by employing an integrated approach that the two interconversions, namely open neutral double right arrow anionic and open neutral double right arrow dianionic, can contribute to the pH- dependent shift in the absorption spectra of BPB. Even though both static and integrated approaches reproduce the pH-dependent red shift in the absorption spectra of BPB, the latter one is suitable to determine both the spectra and spectral broadening. Finally, the computed static first hyperpolarizability for various protonated and deprotonated forms of BPB reveals that this molecule can be used as a nonlinear optical probe for pH sensing in addition to its highly exploited use as an optical probe.
机译：我们通过采用静态和集成方法研究了水溶液中著名的酸碱指示剂溴酚蓝（BPB）的线性和非线性光学性质。在静态方法中，已经使用时变密度泛函理论（TD-DFT）对BPB的中性和不同非质子化形式的完全松弛的几何结构计算了光学性质。此外，还考虑了封闭式和开放式BPB。在集成方法中，使用混合的随时间变化的密度泛函理论/分子力学方法从分子动力学模拟中提取的许多快照中计算了光学特性。静态方法表明，封闭中性双右箭头阴离子互变是BPB吸收光谱从酸性到碱性pH改变的红移的主要机理。通过采用集成方法发现，两个互变，即中性双右箭头和中性双右箭头都可以促进pH依赖性BPB吸收光谱的变化。即使静态方法和集成方法都可以在BPB的吸收光谱中重现pH依赖的红移，但后者适合于确定光谱和光谱展宽。最终，对于各种质子化和去质子化的BPB形式，计算出的静态第一超极化率表明该分子除了被广泛用作光学探针之外，还可以用作用于pH传感的非线性光学探针。

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