Sainudeen Zuhail, Ray Paresh Chandra
Department of Chemistry, Jackson State University, Jackson, Mississippi 39217, USA.
J Phys Chem A. 2005 Oct 13;109(40):9095-103. doi: 10.1021/jp052820+.
We present a time-dependent quantum-chemical analysis on merocyanine aggregates to understand the insight of the intermolecular interactions and to find the relationship between structural and collective nonlinear optical properties. The first hyperpolarizabilities are evaluated for monomer and aggregates of a series of zwitterionic merocyanine dyes, whose synthesis and formation of H and J type aggregates in solvents are reported recently in the literature (J. Am. Chem. Soc. 2002, 124, 9431). The molecular geometries are obtained via B3LYP/6-31G (hybrid density-functional theory) optimization including PCM approach, while the dynamic NLO properties are calculated with the TD-DFT/SOS and ZINDO/CV method including solvent effects. It has been observed that the first hyperpolarizability changes tremendously as monomers undergo aggregation, and the magnitude of first hyperpolarizabilities highly depends on the nature of the aggregates. It is found that solvents play a remarkable role on the structure and first hyperpolarizabilities of merocyanine monomers and aggregates. Changing the solvent from low to high dielectric causes not only an increase in magnitude of beta but also a change in sign, therefore passing through zero at intermediate dielectric. The importance of our results on the design of electrooptic materials have been discussed.
我们对部花青聚集体进行了含时量子化学分析，以深入了解分子间相互作用，并找出结构与集体非线性光学性质之间的关系。我们评估了一系列两性离子部花青染料单体和聚集体的第一超极化率，这些染料的合成以及它们在溶剂中形成H型和J型聚集体的情况最近已有文献报道（《美国化学会志》，2002年，第124卷，第9431页）。分子几何结构通过包含PCM方法的B3LYP/6 - 31G（混合密度泛函理论）优化得到，而动态非线性光学性质则采用包含溶剂效应的TD - DFT/SOS和ZINDO/CV方法进行计算。已观察到，随着单体发生聚集，第一超极化率会发生巨大变化，且第一超极化率的大小高度依赖于聚集体的性质。研究发现，溶剂对部花青单体和聚集体的结构及第一超极化率起着显著作用。将溶剂从低介电常数变为高介电常数不仅会导致β值大小增加，还会引起符号变化，因此在中间介电常数时会经过零点。我们还讨论了这些结果在电光材料设计方面的重要性。
