School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA.
J Phys Chem A. 2011 Mar 24;115(11):2160-8. doi: 10.1021/jp110425r. Epub 2011 Mar 1.
Cyanine-like dyes are promising candidates for third-order nonlinear optical (NLO) applications such as all-optical switching. Here, we examine the consequences for linear and nonlinear optical properties of varying substituents on the central methine unit of bis(dioxaborine)-terminated anionic pentamethines and bis(indole)-terminated cationic heptamethines. The variation in absorption maxima and electrochemical potentials with structure can generally be rationalized using the Dewar-Knott rules, providing that mesomeric and inductive electron-withdrawal and donation are explicitly considered. In the case of nitro- and (dioxaborinyl)vinyl-substituted bis(dioxaborine) pentamethines, the low-energy transitions are significantly broadened, consistent with (1)H NMR spectra indicating deviation from cyanine-like geometry. Real and imaginary parts of the third-order polarizabilities, Re(γ) and Im(γ), were measured at 1.3 μm. The values of Im(γ) indicate that the values of Re(γ) are significantly resonantly enhanced, while the positive value of Re(γ) found for a nitro-substituted dioxaborine example is atypical for a symmetrical polymethine and suggests that a two-state treatment is inadequate. The relevance of these results to chromophore design for third-order NLO applications is discussed.
类似菁染料是三阶非线性光学（NLO）应用的有前途的候选物，例如全光开关。在这里，我们研究了在双（二氧硼烷）末端阴离子五甲川和双（吲哚）末端阳离子十七甲川的中央甲川单元上变化的取代基对线性和非线性光学性质的影响。使用 Dewar-Knott 规则可以合理地解释吸收最大值和电化学势随结构的变化，只要明确考虑离域和诱导的电子吸电子和供电子。对于硝基和（二氧硼基）乙烯基取代的双（二氧硼烷）五甲川，低能量跃迁明显变宽，与（1）H NMR 谱表明偏离菁染料几何形状一致。在 1.3 μm 处测量了三阶极化率的实部 Re(γ)和虚部 Im(γ)。Im(γ)的值表明 Re(γ)的值显著共振增强，而对于硝基取代的二氧硼烷实例，发现 Re(γ)的正值对于对称多甲川来说是不典型的，这表明两态处理是不充分的。讨论了这些结果对三阶 NLO 应用中发色团设计的相关性。
