Cavendish Laboratory, University of Cambridge , J. J. Thomson Avenue, Cambridge, CB3 0HE, U.K.
ACS Appl Mater Interfaces. 2015 Mar 4;7(8):4693-8. doi: 10.1021/am508213c. Epub 2015 Feb 23.
DAST (4-dimethylamino-N-methyl-4-stilbazolium tosylate) is the most commercially successful organic nonlinear optical (NLO) material for frequency-doubling, integrated optics, and THz wave applications. Its success is predicated on its high optical nonlinearity with concurrent sufficient thermal stability. Many chemical derivatives of DAST have therefore been developed to optimize their properties; yet, to date, none have surpassed the overall superiority of DAST for NLO photonic applications. This is perhaps because DAST is an ionic salt wherein its NLO-active cation is influenced by multiple types of subtle intermolecular forces that are hard to quantify, thus, making difficult the molecular engineering of better functioning DAST derivatives. Here, we establish a model parameter, ηinter, that isolates the influence of intermolecular interactions on second-order optical nonlinearity in DAST and its derivatives, using second-harmonic generation (SHG) as a qualifier; by systematically mapping intercorrelations of all possible pairs of intermolecular interactions to ηinter, we uncover a relationship between concerted intermolecular interactions and SHG output. This correlation reveals that a sixfold gain in the intrinsic second-order NLO performance of DAST is possible, by eliminating the identified interactions. This prediction offers the first opportunity to systematically design next-generation DAST-based photonic device nanotechnology to realize such a prospect.
DAST（4-二甲氨基-N-甲基-4-联苯乙烯基甲苯磺酸盐）是用于倍频、集成光学和太赫兹波应用的最成功的商业有机非线性光学（NLO）材料。其成功源于其高光学非线性和足够的热稳定性。因此，已经开发了许多 DAST 的化学衍生物来优化其性能；然而，迄今为止，没有一种衍生物在 NLO 光子学应用方面超过了 DAST 的整体优势。这也许是因为 DAST 是一种离子盐，其 NLO 活性阳离子受到多种类型难以量化的微妙分子间力的影响，从而使得更好地对 DAST 衍生物进行分子工程设计变得困难。在这里，我们使用二次谐波产生（SHG）作为定量标准，建立了一个模型参数 ηinter，该参数可以分离出 DAST 及其衍生物中分子间相互作用对二阶光学非线性的影响；通过系统地将所有可能的分子间相互作用的相互关联映射到 ηinter 上，我们揭示了协同分子间相互作用与 SHG 输出之间的关系。这种相关性表明，通过消除已确定的相互作用，DAST 的固有二阶 NLO 性能可能提高六倍。这一预测为系统地设计基于 DAST 的下一代光子器件纳米技术以实现这一前景提供了第一个机会。
