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Crystalline Nanoporous Frameworks: a Nanolaboratory for Probing Excitonic Device Concepts

Allendorf, Mark D.; Azoulay, Jason A.; Ford, Alexandra C.; Foster, Michael E.; El Gabaly Marquez, Farid E.; Leonard, Francois L.; Leong, Kirsty; Stavila, Vitalie S.; Talin, A.A.; Wong, Brian M.; Brumbach, Michael T.; Van Gough, D.V.; Lambert, Timothy N.; Rodriguez, Mark A.; Spoerke, Erik D.; Wheeler, David R.; Deaton, Joseph C.; Centrone, Andrea C.; Haney, Paul H.; Kinney, R.K.; Szalai, Veronika S.; Yoon, Heayoung P.

Electro-optical organic materials hold great promise for the development of high-efficiency devices based on exciton formation and dissociation, such as organic photovoltaics (OPV) and organic light-emitting devices (OLEDs). However, the external quantum efficiency (EQE) of both OPV and OLEDs must be improved to make these technologies economical. Efficiency rolloff in OLEDs and inability to control morphology at key OPV interfaces both reduce EQE. Only by creating materials that allow manipulation and control of the intimate assembly and communication between various nanoscale excitonic components can we hope to first understand and then engineer the system to allow these materials to reach their potential. The aims of this proposal are to: 1) develop a paradigm-changing platform for probing excitonic processes composed of Crystalline Nanoporous Frameworks (CNFs) infiltrated with secondary materials (such as a complimentary semiconductor); 2) use them to probe fundamental aspects of excitonic processes; and 3) create prototype OPVs and OLEDs using infiltrated CNF as active device components. These functional platforms will allow detailed control of key interactions at the nanoscale, overcoming the disorder and limited synthetic control inherent in conventional organic materials. CNFs are revolutionary inorganic-organic hybrid materials boasting unmatched synthetic flexibility that allow tuning of chemical, geometric, electrical, and light absorption/generation properties. For example, bandgap engineering is feasible and polyaromatic linkers provide tunable photon antennae; rigid 1-5 nm pores provide an oriented, intimate host for triplet emitters (to improve light emission in OLEDs) or secondary semiconducting polymers (creating a charge-separation interface in OPV). These atomically engineered, ordered structures will enable critical fundamental questions to be answered concerning charge transport, nanoscale interfaces, and exciton behavior that are inaccessible in disordered systems. Implementing this concept also creates entirely new dimensions for device fabrication that could both improve performance, increase durability, and reduce costs with unprecedented control of over properties. This report summarizes the key results of this project and is divided into sections based on publications that resulted from the work. We begin in Section 2 with an investigation of light harvesting and energy transfer in a MOF infiltrated with donor and acceptor molecules of the type typically used in OPV devices (thiophenes and fullerenes, respectively). The results show that MOFs can provide multiple functions: as a light harvester, as a stabilizer and organizer or the infiltrated molecules, and as a facilitator of energy transfer. Section 3 describes computational design of MOF linker groups to accomplish light harvesting in the visible and facilitate charge separation and transport. The predictions were validated by UV-visible absorption spectroscopy, demonstrating that rational design of MOFs for light-harvesting purposes is feasible. Section 4 extends the infiltration concept discussed in Section to, which we now designate as "Molecule@MOF" to create an electrically conducting framework. The tailorability and high conductivity of this material are unprecedented, meriting publication in the journal Science and spawning several Technical Advances. Section 5 discusses processes we developed for depositing MOFs as thin films on substrates, a critical enabling technology for fabricating MOF-based electronic devices. Finally, in Section 6 we summarize results showing that a MOF thin film can be used as a sensitizer in a DSSC, demonstrating that MOFs can serve as active layers in excitonic devices. Overall, this project provides several crucial proofs-of- concept that the potential of MOFs for use in optoelectronic devices that we predicted several years ago [ 3 ] can be realized in practice.

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TYPE SAND Report YEAR 2014
OSTIDOI

Luminescent Lanthanide Reporters for High-Sensitivity Novel Bioassays

Fruetel, Julia A.; Foster, Michael E.; Hayden, Carl C.

Biological imaging and assay technologies rely on fluorescent organic dyes as reporters for a number of interesting targets and processes. However, limitations of organic dyes such as small Stokes shifts, spectral overlap of emission signals with native biological fluorescence background, and photobleaching have all inhibited the development of highly sensitive assays. To overcome the limitations of organic dyes for bioassays, we propose to develop lanthanide-based luminescent dyes and demonstrate them for molecular reporting applications. This relatively new family of dyes was selected for their attractive spectral and chemical properties. Luminescence is imparted by the lanthanide atom and allows for relatively simple chemical structures that can be tailored to the application. The photophysical properties offer unique features such as narrow and non-overlapping emission bands, long luminescent lifetimes, and long wavelength emission, which enable significant sensitivity improvements over organic dyes through spectral and temporal gating of the luminescent signal.Growth in this field has been hindered due to the necessary advanced synthetic chemistry techniques and access to experts in biological assay development. Our strategy for the development of a new lanthanide-based fluorescent reporter system is based on chelation of the lanthanide metal center using absorbing chromophores. Our first strategy involves "Click" chemistry to develop 3-fold symmetric chelators and the other involves use of a new class of tetrapyrrole ligands called corroles. This two-pronged approach is geared towards the optimization of chromophores to enhance light output.

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TYPE SAND Report YEAR 2013
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Nano-ordering of donor-acceptor interactions using Metal-Organic Frameworks as scaffolds

ECS Transactions

Leong, Kirsty; Foster, Michael E.; Wong, Bryan M.; Spoerke, Erik D.; Gough, Dara G.; Deaton, Joseph C.; Allendorf, Mark D.

Metal-Organic Frameworks (MOFs) are nanoporous materials with tunable pore sizes that can accommodate and stabilize small molecules. Because of their long-range order and wellunderstood pore environment, the nano-confinement of donoracceptor materials within MOFs offers a new methodology for creating uniform phase-segregated donor-acceptor interfaces. Phase segregation and the photo-physical effects of confining α,ω-Dihexylsexithiophene (DH-6T) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in several MOFs and the potential role of the MOF in creating a nano-heterojunction for organic photovoltaics are discussed. We demonstrate infiltration of both molecules into MOF pores and use luminescence and absorption spectroscopies to characterize the MOF-guest energy transfer processes. Comparison with density functional theory allows us to determine the energetics and band alignment within the MOF. The results demonstrate the utility of MOFs as scaffolds for sub-nanoscale ordering of donor and acceptor species within a highly uniform environment, allowing both the interaction and separation distance to be much more controlled than in the classical bulk heterojunction. © The Electrochemical Society.

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TYPE Conference YEAR 2013
ScopusOSTIDOI
Results 51–75 of 75
Results 51–75 of 75