Publications by authors named "Abhinav Chandresh"

6 Publications

  • Page 1 of 1

Chirality Remote Control in Nanoporous Materials by Circularly Polarized Light.

J Am Chem Soc 2021 May 29;143(18):7059-7068. Epub 2021 Apr 29.

Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.

The ability to dynamically control chirality remains a grand challenge in chemistry. Although many molecules possess chiral isomers, lacking their isolation, for instance during photoisomerization, results in racemic mixtures with suppressed enantiospecific chiral properties. Here, we present a nanoporous solid in which chirality and enantioselective enrichment is induced by circularly polarized light (CPL). The material is based on photoswitchable fluorinated azobenzenes attached to the scaffold of a crystalline metal-organic framework (MOF). The azobenzene undergoes -to--photoisomerization upon irradiation with green light and reverts back to upon violet light. While each moiety in conformation is chiral, we show the isomer also possesses a nonplanar, chiral conformation. During photoisomerization with unpolarized light, no enantiomeric enrichment is observed and both isomers, - and - as well as and -, respectively, are formed in identical quantities. In contrast, CPL causes chiral photoresolution, resulting in an optically active material. Right-CPL selectively excites - and - enantiomers, producing a MOF with enriched -enantiomers, and . The induction of optical activity is reversible and only depends on the light-handedness. As shown by first-principle DFT calculations, while both, and , are stabilized in nonplanar, chiral conformations in the MOF, the isomer adopts a planar, achiral form in solution, as verified experimentally. This shows that the chiral photoresolution is enabled by the linker reticulation in the MOF. Our study demonstrates the induction of chirality and optical activity in solid materials by CPL and opens new opportunities for chiral resolution and information storage with CPL.
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http://dx.doi.org/10.1021/jacs.1c01693DOI Listing
May 2021

Structural and Dynamic Insights into the Conduction of Lithium-Ionic-Liquid Mixtures in Nanoporous Metal-Organic Frameworks as Solid-State Electrolytes.

ACS Appl Mater Interfaces 2021 May 27;13(18):21166-21174. Epub 2021 Apr 27.

Karlsruhe Institute of Technology (KIT), Institute of Functional Interfaces (IFG), Hermann-von-Helmholtz-Platz 1, Eggenstein-Leopoldshafen 76344, Germany.

Metal-organic framework (MOF)-based separators in Li-ion batteries (LIBs) have the potential to improve the battery performance. The mobility and conduction of lithium and organic ionic liquids (ILs) in these materials acting as (quasi) solid-state electrolytes are crucial for the battery power output. Here, we investigate the mobility of a Li-based IL in MOF nanopores and unveil the details of the conduction mechanism by molecular dynamics (MD) simulations. A complex conductivity depending on the Li-IL loading and on the IL composition is observed. Most importantly, the presence of Li prevents the collapse of the conductivity at high IL loadings. The fully atomistic MD simulations including guest-guest and guest-host interactions elucidate the competing mechanisms: Li follows a Grotthuss-like conduction mechanism with large mobility. While at small pore fillings, the Li conduction is limited by the large distance between the anions facilitating the Grotthuss-like conduction; the conduction at high pore fillings is governed by field-induced concentration inhomogeneities. Because of the small MOF pore windows, which hinders the simultaneous passage of the large IL cations and anions in opposite directions, the IL shows field-induced MOF pore blocking and ion bunching. The regions of low anion concentration and high cation concentration represent barriers for Li, decreasing its mobility. In comparison to Li-free IL, the IL bunching effect is attenuated by the formation of charge-neutral Li-anion complexes, resulting in a tremendously increased conductivity at maximum pore filling. The exploitation of this mechanism may enhance the development of advanced batteries based on IL and nanoporous separators.
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http://dx.doi.org/10.1021/acsami.1c00366DOI Listing
May 2021

Programmed Molecular Assembly of Abrupt Crystalline Organic/Organic Heterointerfaces Yielding Metal-Organic Framework Diodes with Large On-Off Ratios.

Adv Sci (Weinh) 2021 Apr 21;8(7):2001884. Epub 2021 Jan 21.

Karlsruhe Institute of Technology (KIT) Institute of Functional Interfaces (IFG) Hermann-von-Helmholtz-Platz 1 Eggenstein-Leopoldshafen 76344 Germany.

Structurally well-defined, crystalline organic/organic heterojunctions between C- and anthracene-based semiconductors are realized via layer-by-layer deposition of metal-organic framework, MOF, thin films. As demonstrated by X-ray diffraction, perfect epitaxy is achieved by adjusting the lattice constants of the two different MOFs. Deposition of top electrodes allows to fabricate p-n as well as n-p devices. Measurements of the electrical properties reveal the presence of high-performance diodes, with a current on/off ratio of up to 6 orders of magnitude and an ideality factor close to unity. The crystalline nature of the abrupt organic/organic heterojunction provides the basis for a rational, simulation-based optimization and tailoring of such organic semiconductor interfaces.
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http://dx.doi.org/10.1002/advs.202001884DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8024988PMC
April 2021

An Enantioselective e-Nose: An Array of Nanoporous Homochiral MOF Films for Stereospecific Sensing of Chiral Odors.

Angew Chem Int Ed Engl 2021 02 15;60(7):3566-3571. Epub 2020 Dec 15.

Karlsruhe Institute of Technology (KIT), Institute of Functional Interfaces (IFG), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany.

Chirality is essential in nature and often pivotal for biological information transfer, for example, via odor messenger molecules. While the human nose can distinguish the enantiomers of many chiral odors, the technical realization by an artificial sensor or an electronic nose, e-nose, remains a challenge. Herein, we present an array of six sensors coated with nanoporous metal-organic framework (MOF) films of different homochiral and achiral structures, working as an enantioselective e-nose. While the achiral-MOF-film sensors show identical responses for both isomers of one chiral odor molecule, the responses of the homochiral MOF films differ for different enantiomers. By machine learning algorithms, the combined array data allow the stereoselective identification of all compounds, here tested for five pairs of chiral odor molecules. We foresee the chiral-MOF-e-nose, able to enantioselectively detect and discriminate chiral odors, to be a powerful approach towards advanced odor sensing.
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http://dx.doi.org/10.1002/anie.202013227DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7898876PMC
February 2021

Interplay of Electronic and Steric Effects to Yield Low-Temperature CO Oxidation at Metal Single Sites in Defect-Engineered HKUST-1.

Angew Chem Int Ed Engl 2020 Jun 17;59(26):10514-10518. Epub 2020 Apr 17.

Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), 76344, Eggenstein-Leopoldshafen, Germany.

In contrast to catalytically active metal single atoms deposited on oxide nanoparticles, the crystalline nature of metal-organic frameworks (MOFs) allows for a thorough characterization of reaction mechanisms. Using defect-free HKUST-1 MOF thin films, we demonstrate that Cu /Cu dimer defects, created in a controlled fashion by reducing the pristine Cu /Cu pairs of the intact framework, account for the high catalytic activity in low-temperature CO oxidation. Combining advanced IR spectroscopy and density functional theory we propose a new reaction mechanism where the key intermediate is an uncharged O species, weakly bound to Cu /Cu . Our results reveal a complex interplay between electronic and steric effects at defect sites in MOFs and provide important guidelines for tailoring and exploiting the catalytic activity of single metal atom sites.
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http://dx.doi.org/10.1002/anie.202000385DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7318571PMC
June 2020

Tailoring Threshold Voltages of Printed Electrolyte-Gated Field-Effect Transistors by Chromium Doping of Indium Oxide Channels.

ACS Omega 2019 Dec 26;4(24):20579-20585. Epub 2019 Nov 26.

Institute of Nanotechnology (INT) and Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Baden-Württemberg, Germany.

Printed systems spark immense interest in industry, and for several parts such as solar cells or radio frequency identification antennas, printed products are already available on the market. This has led to intense research; however, printed field-effect transistors (FETs) and logics derived thereof still have not been sufficiently developed to be adapted by industry. Among others, one of the reasons for this is the lack of control of the threshold voltage during production. In this work, we show an approach to adjust the threshold voltage () in printed electrolyte-gated FETs (EGFETs) with high accuracy by doping indium-oxide semiconducting channels with chromium. Despite high doping concentrations achieved by a wet chemical process during precursor ink preparation, good on/off-ratios of more than five orders of magnitude could be demonstrated. The synthesis process is simple, inexpensive, and easily scalable and leads to depletion-mode EGFETs, which are fully functional at operation potentials below 2 V and allows us to increase by approximately 0.5 V.
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http://dx.doi.org/10.1021/acsomega.9b02513DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6906765PMC
December 2019