Redox-Assisted Self-Assembly of π-Conjugated Chromophores Provides Function-Enhanced Superstructures
Kaixuan Liu, Adam Levy, Chuan Liu, Jean-Hubert Oliver
Department of Chemistry, Cox Science Center, 1301 Memorial Drive, University of Miami, Florida 33124
While nature has mastered the art of engineering non-equilibrium structures that enable energy capture, conversion, and storage with unrivaled efficiency, this level of structural control over synthetic materials with dimensions spanning the nano- to mesoscale remains elusive. Consequently, current technology exploits equilibrium-based strategies to construct organic electronic materials for which molecular interactions and macroscopic organization are neither structurally nor electronically configured for maximum efficiency. Redox-assisted self-assembly of water-soluble perylene diimide will be presented as a new tool to access out-of-equilibrium intermediates through which to navigate the aggregation free energy landscapes and engineer supramolecular assemblies kinetically trapped in local energy minimum. Investigating the electronic properties of these off-equilibrium superstructures using ground-state electronic absorption spectroscopy indicates a 30% enhancement of the exciton bandwidth when compared to equilibrium-constructed architectures. Such modification of nanoscale-object electronic properties exclusively provided by redox-assisted self-assembly originates from a reconfiguration of the superstructure conformation. Examination of the solid-state morphology of assemblies produced through electronically perturbed out-of-equilibrium intermediates reveals complex hierarchical architectures that feature micrometer-long anisotropic domains. To conclude, a preliminary molecular road map to regulate redox-assisted self-assembly will be introduced. The ability to modulate nanoscale-object electronic structure, used in conjunction with facile hierarchical organization offers exceptional promises for the development of optoelectronic materials.
Evidence of Ferrimagnetism in II-VI Dilute Magnetic Quantum Dots
Jasleen K. Bindra1,2, Lavrenty Gutsev1, Sebastian A. Stoian1,2, Johan van Tol2, Kedar Singh3, Geoffrey F. Strouse1, Naresh S Dalal1,2*
1Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA
2National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
3School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067, India
4Department of Physics, Institute of Science, Banaras Hindu University, Varanasi 221005, India
The onset of spin frustration with increasing iron incorporation into wurtzite ZnSe is computationally predicted and experimentally tested. Density functional theory (DFT) models indicate magnetic spin frustration arises due to formation of local Fe-Fe spin lattices within the ZnSe lattice. Comparison of the DFT-GGA spin models to the experimentally prepared 1.8 nm Fe0.1Zn0.9Se QD reveal the predicted spin frustration within the QD is observed by comparison to field and temperature dependent Mossbauer and magnetic susceptibility measurements. The use of computational methods that can anticipate the onset of desirable properties apriori in QDs prior to the synthetic preparation will enhance the toolset of the experimentalist when searching for specific magnetic properties.
Polymer coated lanthanide based nanoparticles as potential PARACEST MRI contrast agents
Pratik Roy, Daniel R. Talham
Department of Chemistry, University of Florida
Lanthanide based Paramagnetic Chemical Exchange Saturation Transfer (PARACEST) agents offer an alternative to T1 and T2 contrast agents. These systems rely on dynamic chemical exchange of labile protons with bulk water and lead to a decrease in magnetization giving negative contrast in MRI. The major advantage is that one can turn ‘on’ and ‘off’ the image contrast by the application of an external radiofrequency pulse. All published examples of PARACEST agents are single molecule systems, although there are potential advantages to particle-based systems. The interaction of double-hydrophilic block copolymers, containing a poly (acrylic acid) block with europium ions in water leads to the spontaneous formation of polymer-coated nanoparticles, with an average diameter near 20 nm. Saturation transfer experiments with these assemblies show a significant decrease in intensity of the bulk water signal, suggesting it’s potential application as a PARACEST agent.
Supermolecular Building Layer (SBL) Approach to MOFs for Biomedical Applications
Jarrod F. Eubank, Christian Beauchemin, Eric Alonso, and Juan Garcia
Florida Southern College
The necessity for materials with targeted functions for various applications has driven scientists to pursue rational synthetic strategies toward design. The relatively recent development of a class of inorganic-organic hybrid materials known as metal-organic frameworks (MOFs) has significantly aided in the advancement of modern synthetic strategies toward functional materials due to their ease of construction and exceptional tenability. Efforts began with the use of simple molecular building blocks (MBBs, resulting in geometric moieties having multi-connectedness (i.e., greater than 2-connected)) and advanced to more hierarchically complex, and thereby more selective, design strategies like the supermolecular building block (SBB) and, more recent, supermolecular building layer (SBL) techniques. These exclusive approaches have opened avenues to materials with unprecedented or previously difficult to attain properties, such as pores lined with free carboxyl groups. Here, we focus on the SBL approach to target materials for biomedical applications. Preliminary work indicates the ability to design and utilize carboxyl-functionalized MOFs for drug delivery applications. In addition, the construction of MOFs via the incorporation of bioactive molecules suggests potential for additional biomedical applications.
Fe3Se4 Phase Stabilized by Transition Metal Doping
Luis A. Saucedo, David Hardy, Geoffrey F. Strouse, Michael Shatruk
Florida State University
With a growing interest in rare-earth free magnetic materials, Fe3Se4 is a promising material, being composed of earth-abundant elements and showing ferrimagnetic ordering at 340 K. In a common synthesis of this material, elemental selenium is used as a precursor, resulting in long reaction times and the presence of ferrimagnetic Fe7Se8 or superconducting FeSe impurity. Herein we show a synthetic route using molecular precursors, which allow not only for shorter reaction times, but also for stabilization of the Fe3Se4 phase by doping with small concentrations of 3d transition metals (e.g., V, Cr, Mn). The synthesis, characterization and magnetic studies of these materials will be discussed.
Revisiting Bond Breaking and Making in the Solid State: Where are the Electrons?
Xiaoyan Tan,1 Alexander A. Yaroslavtsev,2 Vincent Yannello, Zachary P. Tener,1 Daniel Haskel,3 Francois Guillou,4 Andrey Rogalev,4 Michael Shatruk1
1 Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA
2 European XFEL GmbH, 22869 Schenefeld, Germany
3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
4 European Synchrotron Radiation Facility, 71 Avenue des Martyrs, CS40220, Grenoble, France
More than 30 years ago, a seminar paper by Hoffmann and Zheng  addressed the chemical aspects of first-order phase transitions in ThCr2Si2-type structures. They suggested that the breaking and making of the X–X bonds between the [T2X2] layers (X = group 13-16 element; T = transition metal), separated by layers of alkali, alkali-earth, or rare-earth metal atoms (A), correlates with the filling of the electronic d-band of the transition metal. Such correlations have been the focus of many studies on structural, electronic, and magnetic phase transitions in this class of materials.
The structural phase transitions in the ThCr2Si2-type materials involve the collapse or expansion of the structure along the tetragonal c axis, i.e. in the direction parallel to the interlayer X–X bonds. Despite many examples of such transitions being known, the direct experimental assessment of changes in the electron density redistribution between the A and [T2X2] layers upon the formation and breaking of the X–X bonding interactions is largely lacking. Earlier studies by us  and other groups  have revealed fascinating pressure-induced transitions in EuCo2Pn2 (Pn = P, As) which are accompanied by the change in the Eu oxidation state and the transition from the localized (4f) magnetism to itinerant (3d) magnetism. In the present contribution, we demonstrate that the changes in the electron concentration in the [Co2Pn2] layer defy the formal electron-counting rules that are often used for Zintl-like phases. X-ray absorption measurements offer the direct insight into the changes in the Eu oxidation state and magnetism and the associated redistribution of the electron density in the [Co2Pn2] layer.
The research reported in this presentation has been supported by the National Science Foundation under Award DMR-1507233.
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