Facile structure and property tuning through alteration of ring structures in conformationally locked phenyltetraene nonlinear optical chromophores
作者:Xing-Hua Zhou、Joshua Davies、Su Huang、Jingdong Luo、Zhengwei Shi、Brent Polishak、Yen-Ju Cheng、Tae-Dong Kim、Lewis Johnson、Alex Jen
DOI:10.1039/c0jm02855j
日期:——
A series of phenyltetraene-based nonlinear optical (NLO) chromophores 1a–c with the same donor and acceptor groups, but different tetraene bridges that are partly connected by various sizes of aliphatic rings, have been synthesized and systematically investigated. The interposed conjugated tetraene segments in three chromophores studied are based on isophorone, (1S)-(−)-verbenone, and 3,4,4-trimethyl-2-cyclopentenone, respectively. This kind of structural alteration has significant effect on the intrinsic electronic structures and physical properties of these highly polarizable chromophores as revealed by a variety of characterization techniques. The introduction of the verbenone- and trimethylcyclopentenone-based tetraene bridges could significantly improve the glass-forming ability of chromophores 1b and 1c in comparison with the highly crystalline characteristics of isophorone-based chromophores 1a. More importantly, chromophores 1a–c exhibited distinct optical features in absorption band shape, solvatochromic behavior, as well as energy band gap from the UV-vis-NIR absorption measurements. Quantum mechanical calculations using density functional theory (DFT) were also used to evaluate second-order NLO properties of these chromophores. The electro-optic (EO) coefficients of 1a–c in poled polymers with the 10 wt% chromophore content showed an apparent decrease from 78 pm V−1 for 1a to 42 pm V−1 for 1c. This decrease is attributed to the gradual decrease of the molecular hyperpolarizability (β) of the chromophores which is associated with the progressive cyanine-like electronic structure from the isophorone-based 1a to the cyclopentenone-based 1cchromophore.
一系列基于苯基四烯的非线性光学(NLO)染料1a–c被合成并系统研究,这些染料具有相同的供体和受体基团,但四烯桥结构不同,部分通过不同大小的脂肪环相连。三个研究染料中的夹层共轭四烯段分别基于异佛尔酮、(1S)-(−)-蓝桉酮和3,4,4-三甲基-2-环戊烯酮。这种结构改变对这些高极化染料的本征电子结构和物理性质产生了显著影响,这通过多种表征技术得以揭示。与基于异佛尔酮的具有高度结晶特性的染料1a相比,引入蓝桉酮和三甲基环戊烯酮基四烯桥可显著提高染料1b和1c的玻璃形成能力。更重要的是,染料1a–c在吸收带形状、溶剂变色行为以及从紫外-可见-近红外吸收测量得到的能带间隙方面表现出独特的光学特征。采用密度泛函理论(DFT)的量子力学计算也被用于评估这些染料的二阶NLO性质。在极化聚合物中,染料含量为10 wt%时,1a–c的电光(EO)系数从1a的78 pm V−1明显降低到1c的42 pm V−1。这种降低归因于染料分子超极化率(β)的逐渐降低,这与从基于异佛尔酮的1a到基于环戊烯酮的1c染料的渐进式菁菪电子结构有关。