Enhancing Molecular Alignment and Photostability in Organic EO Materials using Single-Molecule Microscopy

使用单分子显微镜增强有机 EO 材料的分子排列和光稳定性

• 批准号: 1005819
• 负责人: Philip Reid
• 金额: $ 41.04万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-01 至 2015-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1005819&HistoricalAwards=false
• 关键词: Enhancing; Molecular; Alignment; Photostability; Organic

Single-molecule spectroscopic techniques will be employed to enhance the efficiency and photostability of organic electro-optic (EO) materials. Recent advances in organic photonic materials and their inclusion into novel device architectures suggests that these materials will play an important role in the next generation of EO switching devices for telecommunications and other applications. Although the promise of organics to provide enhanced EO activity, faster switching speeds, and at a lower cost relative to current materials has been recognized for some time, there are two issues that limit the wide-spread use of these materials: chromophore alignment and photostability. The studies are designed to provide insight into the molecular details underlying these issues, and with this insight strategies for enhanced material performance can be identified and pursued.Alignment in organic EO materials is studied by investigating the rotational dynamics of single-molecules as a function of external perturbation (in particular, electric field and temperature). EO activity arises at the ÷(2) level of material susceptibility which requires that the material non-centrosymmetric. Acentric order in these materials is introduced by poling, a process in which an external electric field interacts with the permanent dipole moment of the chromophore to (theoretically) restrict chromophore reorientation thus providing for material alignment. The molecular-level details of poling are poorly understood, and our recent studies have established that only modest alignment is achieved in this process. Furthermore, poling is generally performed 5 to 10° C below the glass transition temperature of the polymer host, but what do chromophore reorientational dynamics look like at these temperatures? What is the interplay between temperature, polymer relaxation, and poling-induced order? The single molecule studies will provide molecular-level insight into the poling process, and subsequently refinement of this process. Optical poling in binary chromophore organic glasses is also studied. Optical poling provides for a two-fold enhancement in EO activity relative to electric-field poling alone. Theory suggests that this enhancement arises from the optical field reducing the spatial dimensionality of the host. The team will measure the rotational dynamics of single molecule in the presence and absence of the optical poling field to directly test this hypothesis. The photostability of organic EO materials is investigated by measuring the time-dependent emission (blinking), spectral diffusion, and excited-state lifetimes of single molecules. Time-tagged, time-correlated single photon counting techniques are used to directly correlate blinking behavior to the underlying photophysics that result in population and depopulation of the non-emissive or dark state. The experiments are combined with Monte-Carlo simulations to identify these states which serve as a gateway to material photodecomposition. A unique aspect of this work is that the team will employ single molecule crystal isolation techniques to test vexing questions concerning molecular photophysics in complex environments, with the crystal providing a host where solvation is well-defined and controlled.The advancement of fundamental knowledge will have impact on the fields of quantum information and of photonics. The graduate students directly involved in these studies will receive a multidisciplinary education in basic physics, materials science, and nanofabrication. The research, while fundamental in nature, is readily accessible to undergraduates and will benefit from the involvement of undergraduate students in the program. The fundamentals of optical absorption and emission provide unique opportunities for illustrating nanoscience to pre-Kindergarten through high school students. For example, the emission from visible quantum dots provides excellent visual demonstrations that will be used in the outreach activities of the PIs in high needs Buffalo Public Schools. This outreach will be enhanced significantly by the incorporation of a middle school science teacher in the PIs research activities during the summer. Simultaneously, this summer program will also enable the PIs to benefit from the experience of the teacher in the development of educational tools for use at the middle and high school levels. Finally, the PIs will organize a summer workshop for high school students to provide an introduction to the exciting research in nanoscience.

单分子光谱技术将用于提高有机电光（EO）材料的效率和光稳定性。有机光子材料的最新进展及其在新型器件架构中的应用表明，这些材料将在电信和其他应用的下一代电光开关器件中发挥重要作用。尽管人们已经认识到有机物具有增强的环氧乙烷活性、更快的转换速度和相对于现有材料更低的成本，但仍有两个问题限制了这些材料的广泛使用：发色团排列和光稳定性。这些研究旨在深入了解这些问题背后的分子细节，并通过这种洞察来确定和追求增强材料性能的策略。通过研究单分子的旋转动力学作为外部扰动（特别是电场和温度）的函数来研究有机 EO 材料的排列。 EO 活性出现在材料磁化率 ÷(2) 水平，这要求材料非中心对称。这些材料中的偏心顺序是通过极化引入的，在该过程中，外部电场与发色团的永久偶极矩相互作用，以（理论上）限制发色团重新取向，从而提供材料对准。人们对极化的分子水平细节知之甚少，我们最近的研究表明，在此过程中只能实现适度的对齐。此外，极化通常在低于聚合物主体玻璃化转变温度 5 至 10°C 的温度下进行，但在这些温度下发色团重新取向动力学是什么样的？ 温度、聚合物弛豫和极化诱导有序之间的相互作用是什么？单分子研究将为极化过程提供分子水平的洞察，并随后完善该过程。还研究了二元发色团有机玻璃中的光学极化。相对于单独的电场极化，光学极化使 EO 活性增强两倍。理论表明，这种增强是由于光场降低了主体的空间维度而产生的。该团队将测量单分子在存在和不存在光学极化场的情况下的旋转动力学，以直接检验这一假设。通过测量单分子的时间依赖性发射（闪烁）、光谱扩散和激发态寿命来研究有机 EO 材料的光稳定性。时间标记的、时间相关的单光子计数技术用于将眨眼行为与导致非发射或黑暗状态的数量和数量减少的潜在光物理直接关联起来。这些实验与蒙特卡罗模拟相结合，以确定这些状态，作为材料光分解的门户。这项工作的独特之处在于，团队将采用单分子晶体分离技术来测试复杂环境中有关分子光物理的棘手问题，晶体提供了溶剂化被明确定义和控制的宿主。基础知识的进步将对量子信息和光子学领域产生影响。直接参与这些研究的研究生将接受基础物理、材料科学和纳米制造等多学科教育。这项研究虽然本质上是基础性的，但本科生很容易接触到，并将受益于本科生参与该项目。 光学吸收和发射的基础知识为向学前班到高中生展示纳米科学提供了独特的机会。例如，可见量子点的发射提供了出色的视觉演示，将用于高需求布法罗公立学校的 PI 的外展活动。夏季期间，将一名中学科学教师纳入 PI 的研究活动中，将大大加强这种外展活动。同时，这个暑期项目也将使PI能够从教师开发初高中教育工具的经验中受益。最后，PI 将为高中生组织一次夏季研讨会，介绍令人兴奋的纳米科学研究。