Microscopic Charge Transport in Molecularly Doped Organic Materials

下一代电子产品需要能够像金属一样传输电力的材料，但也需要提供新的特性，例如灵活，重量轻，成本低和可回收。 在这方面，塑料等全碳材料很有吸引力，但它们缺乏传统金属的电传输能力。 与金属不同，碳基塑料很少有完美的结构（结晶）。它们的紊乱使得很难确定电流如何流过它们，这是改善其电气性能的必要的第一步。在这个由化学部化学结构，动力学和机制（CSDM-A）计划资助的项目中，明尼苏达大学双城分校的Aaron Massari教授正在使用复杂的激光技术来研究电荷通过复杂分子材料的运动，这些材料可以作为未来的电导体。 该项目的跨学科性质为本科生和研究生提供了一个培训环境，培养了下一代科学家，他们不仅精通台式化学，而且精通电学、显微镜和光谱技术。最终，这项研究不仅可以为现有问题带来新的视角，还可以为电气材料的合理设计提供信息，从而使设备毒性更小，生产所需能源更少。Massari教授担任能源和U展的主任，每年为10，000多名3 - 6年级学生带来科学。该节目充满了充满活力的科学演示和热力学第一定律。 对许多人来说，这项活动介绍了第一次上大学的想法，因为超过一半的与会者是代表性不足的群体的成员。 Massari教授还指导了草原计划大学的化学部分，在那里他和他的研究小组与60名7-12年级的学生和他们的老师一起工作，这些学生来自该州地理上孤立的农村地区。 这些推广和教育活动鼓励STEM职业。该项目的重点是结构参数的作用，如多态性，施主-受主间距，部分电荷转移，和共价连接的分子掺杂剂，在电荷通过基态掺杂的分子薄膜的传输。 该测量利用二维红外（2D-IR）光谱的能力，将特定分子几何形状内的电荷转移速率与高度不均匀的化学环境隔离开来。红外光的短脉冲激发膜中中性和电荷（掺杂）分子的分子振动，然后第二对脉冲探测该激发的演变，作为电荷位置随时间变化的标记。 将振动光谱分解为第二维允许人们独立于其他分子监测特定分子构型的电荷转移动力学，从而可以解决传输动力学本身。 这项工作系统地测试了微观分子间距和顺序对宏观电输运的影响，方法是使用具有特定结构修饰的分子，这些结构修饰以已知的方式影响它们的堆积。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Next generation electronics require materials that can transport electricity like metals but also offer new properties such as being flexible, light weight, low-cost, and recyclable. In this regard, all-carbon materials such as plastics are attractive, but they lack the electrical transport ability of traditional metals. Unlike metals, carbon-based plastics are rarely perfectly structured (crystalline). Their disorder makes it difficult to determine how electricity flows through them, a necessary first step in improving their electrical performance. In this project funded by the Chemical Structure, Dynamics, and Mechanisms (CSDM-A) program of the Chemistry Division, Professor Aaron Massari of the University of Minnesota-Twin Cities is using sophisticated laser techniques to study the movement of electrical charges through complex molecular materials that could act as future electrical conductors. The interdisciplinary nature of the project supports a training environment for undergraduate and graduate students that produces next-generation scientists who are skilled in benchtop chemistry, but also electrical, microscopic, and spectroscopic techniques. Ultimately, the research may not only lead to new perspectives on existing problems, but also inform the rational design of electrical materials leading to devices that are less toxic and require less energy to produce. Professor Massari serves as the Director of the Energy and U Show, which brings science to over 10,000 3rd-6th graders each year. The show is filled with vibrant scientific demonstrations and the First Law of Thermodynamics. For many, the event introduces the idea of attending college for the first time as more than half of the attendees are members of underrepresented groups. Professor Massari also directs the chemistry portion of the University on the Prairie program, where he and his research group travel to work with 60 students in grades 7-12 and their teachers from rural, geographically isolated portions of the state. These outreach and educational activities encourage STEM careers. The project focuses on the roles of structural parameters, such as polymorphism, donor-acceptor spacing, partial charge transfer, and covalent attachment of molecular dopants, in the transport of charge through ground-state doped molecular thin films. The measurements leverage the ability of two-dimensional infrared (2D-IR) spectroscopy to isolate the rates of charge transfer within specific molecular geometries from highly heterogeneous chemical environments. Short pulses of infrared light excite molecular vibrations on neutral and charge (doped) molecules in a film and then a second pair of pulses probe the evolution of that excitation as a marker for the location of the charge as a function of time. Resolving the vibrational spectrum into a second dimension allows one to monitor the kinetics of charge transfer for specific molecular configurations independent of the others so that the transport kinetics can themselves be resolved. The work systematically tests the impact of microscopic molecular spacing and order on macroscopic electrical transport by using molecules with particular structural modifications that affect their packing in known ways. Electrical transport is also driven in-situ in samples while they are characterized by 2D-IR spectroscopy.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.