Can we still measure circular dichroism with circular dichroism spectrometers: The dangers of anisotropic artifacts
Can we still measure circular dichroism with circular dichroism spectrometers: The dangers of anisotropic artifacts
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DOI：
10.1002/chir.23597
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发表时间：
2023-06-18
期刊：
影响因子：
2
通讯作者：
Robinson，Richard D.
中科院分区：
文献类型：
--
作者：
Ugras，Thomas J.;Yao，Yuan;Robinson，Richard D.
具有强线性各向异性的手性材料由于线性二色性（LD）和双折射（LB）对其光谱的人为影响，难以用圆二色性（CD）精确表征。从历史上看，研究人员已经在穆勒矩阵上使用二阶泰勒级数展开来模拟传统材料中LDLB相互作用对光谱的影响，但这种方法可能不再足以解释紧急材料中的人造CD信号。在这项工作中，我们提出了一个使用三阶展开来模拟测量CD的表达式，该表达式引入了“成对干扰”项，与LDLB项不同，这些项不能从信号中平均出来。我们发现，三阶对偶干涉项对模拟的CD光谱有显著的贡献。通过对测量的CD在广泛的线性和手性各向异性参数范围内的数值模拟，LDLB相互作用在具有强线性各向异性（LD， LB）但手性各向异性可以忽略的样品中最为突出，其中测量的CD在大于103的因素下偏离手性诱导的CD。此外，在具有中至强手性和线性各向异性的系统中，配对相互作用最为显著，其中测量到的CD膨胀了两倍，随着线性各向异性接近最大值，这个数字会增长。总之，具有中强线性各向异性的介质，其CD极有可能被这些微妙的影响所改变。这项工作强调了在高各向异性纳米材料中通过高阶成对干涉效应来考虑CD测量中的畸变的重要性。
Chiral materials with strong linear anisotropies are difficult to accurately characterize with circular dichroism (CD) because of artifactual contributions to their spectra from linear dichroism (LD) and birefringence (LB). Historically, researchers have used a second‐order Taylor series expansion on the Mueller matrix to model the LDLB interaction effects on the spectra in conventional materials, but this approach may no longer be sufficient to account for the artifactual CD signals in emergent materials. In this work, we present an expression to model the measured CD using a third‐order expansion, which introduces “pairwise interference” terms that, unlike the LDLB terms, cannot be averaged out of the signal. We find that the third‐order pairwise interference terms can make noticeable contributions to the simulated CD spectra. Using numerical simulations of the measured CD across a broad range of linear and chiral anisotropy parameters, the LDLB interactions are most prominent in samples that have strong linear anisotropies (LD, LB) but negligible chiral anisotropies, where the measured CD strays from the chirality‐induced CD by factors greater than 103. Additionally, the pairwise interactions are most significant in systems with moderate‐to‐strong chiral and linear anisotropies, where the measured CD is inflated twofold, a figure that grows as linear anisotropies approach their maximum. In summary, media with moderate‐to‐strong linear anisotropy are in great danger of having their CD altered by these effects in subtle manners. This work highlights the significance of considering distortions in CD measurements through higher‐order pairwise interference effects in highly anisotropic nanomaterials.