Energy and Electron Transport in pi-Stacked Multichromophoric Assemblies: Global Dynamics from the Gas to Condensed Phase

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In this project funded by the Macromolecular, Supramolecular and Nanochemistry program of the Chemistry Division, Professors Rajendra Rathore and Scott Reid of Marquette University will examine model molecular assemblies that incorporate stacked polycyclic aromatic hydrocarbons. Such interactions are characteristic of many molecular assemblies, including those found in nature (e.g., DNA), and an understanding of the transport of electrons and energy through such assemblies is critical to develop new charge-transfer materials of increased efficiency for applications in photovoltaic devices, molecular electronics, and nanotechnology. To meet this challenge, the synthesis of carefully designed molecular assemblies is carried out, and the assemblies characterized using a variety of experimental strategies based on molecular spectroscopy, supported by computational chemistry. Supramolecular assemblies exploit a variety of covalent and non-covalent scaffolding interactions. Of these, pi-stacking is important. The efficiency of long range charge transfer in the conducting layers of photovoltaic devices is governed not only by the intramolecular electron transport through the backbone of polymers but also by the intermolecular electron transport through bulk material, where the amorphous assembly of pi-conjugated molecules is generally randomized. As cyclophane-like aromatic dimers and their cation radicals represent the simplest fundamental units responsible for charge transport in bulk materials, the design and synthesis of modern organic materials for the emerging area of molecular electronics and nanotechnology demands a thorough understanding of electron and energy-transfer processes in carefully designed cofacially-arrayed molecules. This project addresses fundamental questions concerning the flow of energy and electron transfer in model multichromophoric systems and developes new strategies for exploiting such assemblies as light driven actuators, taking advantage of the molecular rearrangement which accompanies oxidation or electronic excitation. Examining broader impacts, this work informs the design and synthesis of next generation organic materials for applications in the area of molecular electronics and photovoltaics.