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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Understanding the Second-Order Nonlinear Optical Properties of One-Dimensional Ruthenium(II) Ammine Complexes
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Understanding the Second-Order Nonlinear Optical Properties of One-Dimensional Ruthenium(II) Ammine Complexes

机译：了解一维钌（II）氨基配合物的二阶非线性光学性质

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摘要

First principles calculations of the linear and nonlinear optical properties are carried out for three series of one-dimensional ruthenium(II) ammine complexes with one pyridyl pyridinium ligand containing different numbers of C2H2 units or the (CH=CH)— Ph— (CH=CH) linker. The substitution effects upon introducing one pyridine or one N-methylimidazole moiety as donor instead of ammonia have also been studied in detail. These calculations employing density functional theory with different exchange-correlation functional as well as the polarizable continuum model approach to describe the solvent effects show that these compounds are challenging for theoretical chemistry and that their nonlinear optical responses are complex and depend on many structural and electronic factors. Two major types of methods have been employed to calculate and analyze the first hyperpolarizabilities (β): (i) the summation-over-states scheme, applied to calculate the longitudinal β tensor component, truncated to one or two dominant excited states, of which the results are compared to Stark spectroscopy data, and (ii) the quadratic response schemes, providing the whole second harmonic generation response of the compound, which can be compared to the values derived from hyper-Rayleigh scattering measurements. Using response theory calculations, off-resonant first hyperpolarizability values display a monotonic increase as a function of the number of C2H2 units (from 0 to 3 units, corresponding to compounds 1—4, respectively) in the pyridyl pyridinium ligand (in the three series with NH3, pyridine, and N-methylimidazole substituent in opposite position to the large ligand). These calculations, which evidence the dominance of the longitudinal β tensor component and a consistent depolarization ratio close to 5.0, also predict a smaller β value when the (CH=CH)3 linker of the pyridyl pyridinium ligand (compound 4) is replaced by the (CH—CH)—Ph—(CH=CH) linker (compound 5). To some extent, the calculations performed at a wavelength of 1064 nm confirm these trends, despite the presence of resonance enhancements. Calculations carried out within the summation-overstates scheme to analyze the origin of these β variations reproduce the monotonic increase of β in the 1 —4 series, but compounds 4 and 5 are predicted to have similar β values. Upon relating these β variations to those of spectroscopic properties like the excitation energies, transition dipoles, and dipole moments of a pair of excited states (a low-energy metal to ligand charge transfer and a high-energy intraligand charge transfer excited state), the calculations point out the impact of including a second excited state in the treatment, since it leads to a decrease ofβ by about 50%. Though substituting the ammonia group by a pyridine has a limited impact on the linear and nonlinear optical properties of the complexes, the substitution by N-methylimidazole increases β by about 25%, which has been attributed to the contribution of N-methylimidazole to the HOMO and the subsequent bathochromic shifts of the excitation energies. In most of the cases, qualitative and even semiquantitative agreement is observed between theory and experiment, which enables one to get a deep insight into the structure/property relationships of these molecules. When this is not the case, we elaborate on the limitations of the methods of calculations and of the experimental treatments of the measured data.
机译：对具有一个含有不同数量的C2H2单元或（CH = CH）-Ph-（CH =的吡啶基吡啶鎓配体）的三个系列的一维钌（II）氨基配合物进行了线性和非线性光学性质的第一性原理计算。 CH）链接器。还已经详细研究了引入一个吡啶或一个N-甲基咪唑部分作为供体而不是氨的取代作用。这些使用具有不同交换相关函数的密度泛函理论以及可极化连续谱模型方法描述溶剂效应的计算表明，这些化合物对理论化学具有挑战性，并且它们的非线性光学响应是复杂的，并且取决于许多结构和电子因素。已采用两种主要方法来计算和分析第一个超极化率（β）：（i）求和态方案，用于计算被截断为一个或两个主激发态的纵向β张量分量，其中将结果与Stark光谱数据进行比较，以及（ii）二次响应方案，提供化合物的整个二次谐波生成响应，可以将其与从超瑞利散射测量得出的值进行比较。使用响应理论计算，非共振的第一超极化率值显示吡啶基吡啶鎓配体（在三个系列中）的C2H2单元数（从0到3个单元，分别对应于化合物1-4）的单调增加。 NH3，吡啶和N-甲基咪唑取代基的位置与大配体相反）。这些计算证明了纵向β张量分量的优势以及一致的去极化比接近5.0，当吡啶基吡啶配体（化合物4）的（CH = CH）3接头被化合物取代时，β值也较小。 （CH-CH）-Ph-（CH = CH）接头（化合物5）。在某种程度上，尽管存在共振增强，但在1064 nm波长处执行的计算仍确认了这些趋势。在总和过高状态方案中执行的分析这些β变异起源的计算可重现1-4系列中β的单调增加，但化合物4和5预计具有相似的β值。将这些β变化与诸如激发能，跃迁偶极子和一对激发态（低能金属向配体的电荷转移和高能内配体电荷的转移激发态）的光谱性质（例如激发能，跃迁偶极子和偶极矩）相关联后，计算指出在治疗中包括第二激发态的影响，因为它导致β降低约50％。尽管用吡啶取代氨基团对络合物的线性和非线性光学性能影响有限，但被N-甲基咪唑取代的β值增加了约25％，这归因于N-甲基咪唑对HOMO的贡献以及随后激发能的红移。在大多数情况下，理论和实验之间观察到定性甚至半定量的一致性，这使人们可以深入了解这些分子的结构/性质关系。如果不是这种情况，我们将详细说明测量数据的计算方法和实验处理的局限性。

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