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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Large Off-Diagonal Contribution to the Second-Order Optical Nonlinearities of Λ-Shaped Molecules
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Large Off-Diagonal Contribution to the Second-Order Optical Nonlinearities of Λ-Shaped Molecules

机译：Off型分子的二阶光学非线性的大对角贡献

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摘要

The diagonal and off-diagonal tensor components of the first hyperpolarizability of a series of Λ-shaped molecules are compared by means of ab initio and semiempirical molecular orbital calculations. The calculated results are rationalized using expressions derived from a simple valence-bond charge-transfer model in which one ground and two excited state are described as a combination of one valence-bond (VB) and two charge-transfer (CT) states. In addition to the CT character, the angle (2θ) between the two donor (D)/acceptor (A) branches is a key parameter to determine the relative magnitudes between the β_(xxz) and β_(zzz) components. In the VB-2CT model, β_(xxz) presents a maximum value for 2θ = 109.47°, whereas β_(xxz) and μ_z have the same sign. On the other hand, β_(zzz) decreases monotonically with θ, and its variations with the CT character follow a curve with two extrema like for one-dimensional D/A chromophores. The ab initio and semiempirical calculations as well as the VB-2CT model show that Λ-shaped molecules with large first hyperpolarizability and specific η = β_(xxz)/β_(zzz) can be designed in order to build phase-matchable second-harmonic generation crystals.
机译：通过从头算和半经验分子轨道计算，比较了一系列Λ形分子的第一个超极化性的对角和非对角张量分量。使用从简单价键电荷转移模型导出的表达式来合理化计算结果，其中一个基态和两个激发态被描述为一个价键（VB）和两个电荷转移（CT）状态的组合。除CT特性外，两个施主（D）/受主（A）分支之间的夹角（2θ）是确定β_（xxz）和β_（zzz）分量之间相对大小的关键参数。在VB-2CT模型中，β_（xxz）表示2θ= 109.47°的最大值，而β_（xxz）和μ_z具有相同的符号。另一方面，β_（zzz）随θ单调减少，其CT特性的变化遵循一维D / A发色团的两个极值曲线。从头算和半经验计算以及VB-2CT模型表明，可以设计具有大的第一超极化性和特定η=β_（xxz）/β_（zzz）的Λ形分子，以建立相位匹配的二次谐波一代晶体。

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