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首页> 外文期刊>Physical chemistry chemical physics: PCCP >Cationic cyanine dyes: impact of symmetry-breaking on optical absorption and third-order polarizabilities
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Cationic cyanine dyes: impact of symmetry-breaking on optical absorption and third-order polarizabilities

机译：阳离子花青染料：对称断裂对光吸收和三阶极化率的影响

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摘要

A systematic study is carried out to find the exact crossover point from symmetric to asymmetric configurations (symmetry-breaking) in a series of cationic cyanine dyes. Hybrid density functional with varying exact-exchange admixture has been used to understand the impact of HF exchange both in the gas phase and in the presence of dielectric medium. This approach provides a basis for understanding the electronic structure and photophysical properties of cyanine dyes. The crossover points predicted using this method are in good agreement with the experiment. The SAC-CI method is used to evaluate the lowest S0→ S1 transition energies in the gas phase. These transitions are preferably dominated by the promotion of an electron from HOMO → LUMO. The average static third-order polarizabilities, (y), are obtained within the three-state model approximation. The analysis showed that for symmetric cyanines, the calculated (γ) values are large and negative, mainly originated from the large S0 → S1 transition moments and small S0 → S1 transition energies. For asymmetric cyanines, the (γ) values are positive and mainly originate from the large change in the ground and first excited state dipole moments. However, both configurations do not include contributions from the two-photon absorption. Further, the localization of charge densities in the HOMO and LUMO indicates that the symmetric and asymmetric cyanines act as promising materials for molecular wires and molecular switches which are fundamental building blocks for molecular electronic devices.
机译：进行了系统的研究，以发现一系列阳离子花菁染料中从对称构型到不对称构型（对称断裂）的确切交点。具有变化的精确交换掺合物的混合密度泛函已被用于理解HF交换在气相和介电介质存在下的影响。该方法为理解花菁染料的电子结构和光物理性质提供了基础。使用该方法预测的交叉点与实验非常吻合。 SAC-CI方法用于评估气相中最低的S0→S1跃迁能。这些跃迁优选地由来自HOMO→LUMO的电子的促进来支配。在三态模型逼近内获得平均静态三阶极化率（y）。分析表明，对于对称花菁，计算得出的（γ）值大而为负，主要来自大的S0→S1跃迁矩和小的S0→S1跃迁能。对于不对称花菁，（γ）值为正，并且主要源自基态和第一激发态偶极矩的大变化。但是，两种配置均不包括双光子吸收的贡献。此外，HOMO和LUMO中电荷密度的定位表明，对称和不对称的花菁可作为分子线和分子开关的有前途的材料，而分子线和分子开关是分子电子设备的基本构建模块。

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