Quantum Interference and Coherence Effects on Charge Transport in Organic Semiconductors

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Nontechnical description: This project addresses preparation and investigation of new materials made of organic molecules possessing electronic properties that enhance the performance of semiconductors. These electronic properties determine how electrons flow along multiple possible pathways in the semiconductor, and therefore are anticipated to affect the material's behavior. Optical probe techniques utilizing ultra-fast lasers are implemented to understand the details of electronic charge transport in semiconductors comprising these new organic molecules. Such semiconductors may be utilized to significantly enhance the performance of ultra-fast optical or electronic devices that are at the core of communications and information technologies. These inexpensive materials, while attractive for implementing improvements to device performance, may therefore also have major impact on the economy. This project encompasses a wide variety of disciplines in materials science, offering training opportunities to scientists at all academic levels. Outreach plans further include ongoing efforts at Northwestern University to integrate students in grades K-12 in educational activities.Technical description: Photo-initiated charge transfer events in organic semiconductors can occur over a very large range of timescales. However, the uniquely quantum mechanical aspect of electronic coherence generally persists for only 10s to 100s of femtoseconds (fs). This project designs and synthesizes new organic semiconductors to more easily detect and exploit these electronic coherences, and to investigate how the consequences of coherent charge transfer can be used to enhance charge generation and transport in organic semiconductors. Femtosecond time-resolved spectroscopies are used to study the charge transport dynamics at the earliest stages, where the influence of electronic coherences is manifest. More specifically, this project is investigating how coherent charge transfer from a donor to two or more electron acceptors occurs within molecular building blocks of organic semiconductors. Separately, the project investigates coherent charge transfer in thin solid films of organic semiconductors. Additionally, the influence of quantum interference in multi-path charge transfer processes on the rate and efficiency of electron-hole pair production in organic semiconductors is addressed. The ability to tailor the design and performance of organic semiconductors via quantum coherence effects is anticipated to enhance semiconductor device performance, therefore impacting electronic and photonic devices commonly used in modern communications and information technologies.