Polyoxometalate-Containing Linear-Dendritic Hybrids As Novel Optoelectronic Materials

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TECHNICAL SUMMARYThe scientific objective of this proposal is to develop a novel hybrid photovoltaic material which combines broad light-harvesting, efficient and directional energy transfer, efficient photoinduced charge separation, and bipolar charge transport. Specifically, a linear-dendritic diblock system will be designed where one end is a tribenzopentaphene (TBP)-based light-harvesting conjugated dendron while the other end is a polyoxometalate (POM)-containing linear polymer. These two different architectures are joined together by a diimido-functionalized POM cluster as the core. At the molecular level the conjugated dendrons are expected to harvest and funnel the photon energy unidirectionally to the core where photoinduced electron transfer will occur through the ligand-to-metal charge transfer transition. In bulk, the linear/dendritic system is so designed that the strong pi-pi stacking interaction among TBP rings and the architectural contrast between the linear block and the dendritic block should promote phase-separation to form pi-stacked dendron-aggregated conjugated domains and cluster-rich domains. The cluster-rich domain transports electrons while the pi-conjugated dendron domain transports holes. The proposed hybrids are thus potentially highly efficient PV materials with long-term stability.The intellectual merit of the project lies not only in the development of new materials including a new type of light-harvesting dendrimer (LHD) based on polycyclic aromatic hydrocarbon building blocks, and the first POM-containing linear-dendritic hybrids, but also in the fundamental understanding of exciton decay pathways, energy transfer dynamics, and electron transfer thermodynamics and kinetics of these light-harvesting materials. In addition, insight into how nanosized and charged POM clusters affect the linear-dendritic diblock copolymer self-assembly can be gained. NON-TECHNICAL SUMMARYThis project is aimed at developing new hybrid materials for photovoltaic (solar-cell) applications. These materials contain polymers and other complex, highly branched planar organic molecules that will be combined in special molecular architectures. These would include a molecular light-harvesting component and the ability of parts of the molecules to form stacks to direct the transport of electrical charges. The broader impact of the proposed activities stems from the project's multidisciplinary nature, its potential technological advances, and its integration with education and outreach. The technological impact of demonstrating and testing a novel hybrid polymer design for solar cell applications is directly related to the broader challenge of energy sustainability. The training under this program will offer students opportunities to develop skills in many areas from chemical synthesis to materials characterization and device fabrication and evaluation. The project will also allow the PIs to continue to expand their outreach efforts toward underrepresented students in science and technology.