Using Circularly Polarized Light to Probe Electronic Excitations in Organic Supramolecular Assemblies

本奖项由2009年美国复苏和再投资法案(公法111-5)资助。技术摘要本奖项由材料研究部和化学部资助。它支持低聚物/聚合物薄膜如何与光相互作用和发光的理论研究和教育。PI的目的是通过研究适合圆二色谱和圆偏振发光光谱的手性超分子结构来研究有机组装中的基本激发。与未极化的光谱相比，这些光谱对扩展的分子间相互作用以及基本电子激发的结构更敏感。这项研究特别感兴趣的是由功能化的共轭分子发色团组成的圆周率堆积的螺旋棒状聚集体，这些发色团在溶液中或在DNA模板的帮助下自组装。具体目标包括：1.详细了解圆偏振发光不对称光谱中的激子特征。在螺旋棒聚集体和手性聚合物薄膜中观察到的光谱随着波长的增加而异常消失，这包含了关于发射物种的解剖的重要信息。这一光谱在光谱探测器中是独一无二的，因为它对核心振动激发周围的内球畸变场具有高度的敏感性。目的是了解极化子半径、重组能和相干长度对圆偏振发光不对称谱的形状和大小的影响。与实验者的国际合作将使低聚硫吩类纳米纤维的应用成为可能。2.严格分析了螺旋杆N-MERS中的分子间相互作用。具有可控数量的发色团的聚集体是严格评估延长分子间相互作用和无序的理论模型的理想系统。即使在激子只局限于少数几个生色团的强无序体系中，圆偏振发光不对称光谱及其吸收类似物也是长程相互作用的灵敏探针。PI旨在对吸收光谱进行详细的理论分析，以帮助解决这些问题。3.评价强激子-声子耦合系统中的激子-棉花效应。在具有强激子-声子耦合的组件中，圆二向色性谱比发现的弱耦合的简单的Cotton对要复杂得多。PI旨在为激子极化子的圆二向色性响应发展一个全面的理论，以了解如何从谱线形状中提取关于分子间相互作用和聚集形态的信息。将应用于无处不在的、具有生物重要性的类胡萝卜素聚集体。上述分析将基于霍尔斯坦哈密顿量。在两粒子近似下，激子相互作用、线性激子-声子耦合和无序将被平等地处理，这将在不牺牲精度的情况下将基组减少到可处理的大小。拟议活动的更广泛影响将主要通过增进对一类技术上重要的材料的了解而感受到，这可能导致改进有机发光二极管和太阳能电池的新设计战略。通过柔性显示器、电子标签和固态照明等产品，软电子设备的商业影响力预计将在未来几年大幅增加。此外，拟议的活动将通过国际合作加强研究基础设施。该奖项由材料研究部和化学部资助。它支持关于由一类长链分子和聚合物组成的薄膜如何与光相互作用并发光的理论研究和教育。这项研究的重点是阻碍人们理解这些薄膜与光相互作用的机制、这些材料如何吸收光以及吸收光后电子态的性质的关键问题。Pi？S方法的一个重要特点是考虑了电子电荷与分子链振动的相互作用。特定类型聚合物的薄膜可用作有机电子设备的活性材料，如晶体管、发光二极管和太阳能电池。这一研究项目有助于为将这些材料用于照明、太阳能转换和其他电子设备提供智力基础。通过柔性显示器、电子标签和固态照明等产品，软电子设备的商业影响力预计将在未来几年大幅增加。此外，拟议的活动将通过国际合作加强研究基础设施。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).TECHNICAL ABSTRACTThis award is funded by the Division of Materials Research and the Chemistry Division. It supports theoretical research and education on how oligomer/polymer films interact with and emit light. The PI aims to investigate fundamental excitations in organic assemblies by focusing on chiral supramolecular structures which are amenable to circular dichroism and circularly polarized luminescence spectroscopies. Compared with their unpolarized counterparts, these spectroscopies are far more sensitive to extended intermolecular interactions as well as the structure of the fundamental electronic excitations. Of particular interest to this study are pi-stacked helical rod aggregates consisting of functionalized conjugated molecular chromophores which self-assemble in solution or with the aid of a DNA template. Specific goals include: 1. A detailed understanding of the excitonic signatures in the circularly polarized luminescence dissymmetry spectrum. The unusual demise of the spectrum with increasing wavelength observed in helical rod aggregates and chiral polymer films contains vital information on the anatomy of the emitting species. This spectrum is unique amongst spectral probes in its high sensitivity to the inner-sphere distortion field surrounding the core vibronic excitation. The objective is to understand how the polaron radius, the reorganization energy, and the coherence length impact the shape and magnitude of the circularly polarized luminescence dissymmetry spectrum. International collaboration with experimentalists will enable applications to oligothiophene nanofibers. 2. A rigorous analysis of intermolecular interactions in helical rod N-mers. Aggregates with a controllable number of chromophores are ideal systems with which to rigorously evaluate theoretical models for extended intermolecular interactions and disorder. The circularly polarized luminescence dissymmetry spectrum and its absorption analog are sensitive probes of long-range interactions even in strongly disordered systems where excitons are localized to only a few chromophores. The PI aims to perform a detailed theoretical analysis of the absorption spectrum to help resolve these issues. 3. An appreciation of the exciton Cotton effect in systems with strong exciton-phonon coupling. In assemblies with strong exciton-phonon coupling the circular dichroism spectrum is far more complex than the simple Cotton couplet found for weak coupling. The PI aims to develop a comprehensive theory for the circular dichroism response of excitonic polarons to understand how information regarding intermolecular interactions and the aggregate morphology can be extracted from the spectral line shape. Applications to the ubiquitous and biologically-important carotenoid aggregates will be made. The above analyses will be based on a Holstein Hamiltonian. Excitonic interactions, linear exciton-phonon coupling, and disorder will be treated on equal footing under the two-particle approximation, which reduces the basis set to a tractable size without sacrificing accuracy. The broader impact of the proposed activities will be felt primarily through an enhanced understanding of a technologically important class of materials, possibly resulting in novel design strategies for improved organic light-emitting diodes and solar cells. The commercial impact of soft electronic devices is expected to dramatically increase over the next several years, through products like flexible displays, electronic labels and solid-state lighting. In addition, the proposed activities will enhance research infrastructure through international collaborations. NONTECHNICAL ABSTRACTThis award is funded by the Division of Materials Research and the Chemistry Division. It supports theoretical research and education on how thin films composed of a class of long chain molecules, polymers, interact with and emit light. The research is focused on key issues that impede understanding of the mechanisms by which these films interact with light, how light is absorbed by these materials and the nature of the electronic states after absorbing light. A key feature of the PI?s approach is to account for the interaction of electronic charge with vibrations of the molecular chains. Thin films of particular kinds of polymers may be useful as active materials for organic-based electronic devices such as transistors, light emitting diodes, and solar cells. This research project contributes to the intellectual foundations that will enable the use of these materials for lighting, solar energy conversion, and other electronic devices. The commercial impact of soft electronic devices is expected to dramatically increase over the next several years, through products like flexible displays, electronic labels and solid-state lighting. In addition, the proposed activities will enhance research infrastructure through international collaborations.