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Rohwer, Lauren E. S.

Publications and source records attributed to Rohwer, Lauren E. S..

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Optical tags comprising rare earth metal-organic frameworks

Optical tags provide a way to identify assets quickly and unambiguously, an application relevant to anti-counterfeiting and protection of valuable resources or information. The present invention is directed to a tag fluorophore that encodes multilayer complexity in a family of heterometallic rare-earth metal-organic frameworks (RE-MOFs) based on highly connected polynuclear clusters and carboxylic acid-based linkers. Both overt (visible) and covert (near infrared, NIR) properties with concomitant multi-emissive spectra and tunable luminescence lifetimes impart both intricacy and security. Tag authentication can be validated with a variety of orthogonal detection methodologies. The relationships between structure, composition, and optical properties of the family of RE-MOFs can be used to create a large library of rationally designed, highly complex, difficult to counterfeit optical tags.

Sava Gallis, Dorina F.↗
DOE OSTI2023

Improved quantum yield in geometrically constrained tetraphenylethylene-based metal–organic frameworks

In this paper we report the synthesis of a novel, tetraphenylethylene-based ligand for metal–organic frameworks (MOFs). Incorporation of this ligand into a Zn- or Eu-based MOF increased the quantum yield (QY) by almost 2.5× compared to the linker alone. Furthermore, the choice of guest solvent impacted the QY and solvatochromatic response. These shifts are consistent with solvent dielectric constant as well as molecular polarizability.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Crystal Prediction and Design of Tunable Light Emission in BTB–Based Metal–Organic Frameworks

Metal-organic frameworks (MOFs) have recently been shown to exhibit unique mechanisms of luminescence based on charge transfer between structural units in the framework. These MOFs have the potential to be structural tuned for targeted emission with little or no metal participation. Here a computationally led, material design and synthesis methodology is presented that elucidates the mechanisms of light emission in interpenetrated structures comprised of metal centers (M = In, Ga, InGa, InEu) and BTB (1,3,5-Tris(4-carboxyphenyl)benzene) linkers, forming unique luminescent M-BTB MOF frameworks. Gas phase and periodic electronic structure calculations indicate that the intensity of the emission and the wavelength are overwhelmingly controlled by a combination of the number of interacting stacked linkers and their interatomic spacings, respectively. In the MOF, the ionic radii of the metal centers primarily control the expansion or shrinkage of the linker stacking distances. Experimentally, multiple M-BTB-based MOFs are synthesized and their photoluminescence was tested. Experiments validated the modeling by confirming that shifts in the crystal structure result in variations in light emission. Through this material design method, the mechanisms of tuning luminescence properties in interpenetrated M-BTB MOFs have been identified and applied to the design of MOFs with specific wavelength emission based on their structure.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Encoding Multilayer Complexity in Anti‐Counterfeiting Heterometallic MOF‐Based Optical Tags

Abstract Optical tags provide a way to quickly and unambiguously identify valuable assets. Current tag fluorophore options lack the tunability to allow combined methods of encoding in a single material. Herein we report a design strategy to encode multilayer complexity in a family of heterometallic rare‐earth metal–organic frameworks based on highly connected nonanuclear clusters. To impart both intricacy and security, a synergistic approach was implemented resulting in both overt (visible) and covert (near‐infrared, NIR) properties, with concomitant multi‐emissive spectra and tunable luminescence lifetimes. Tag authentication is validated with a variety of orthogonal detection methodologies. Importantly, the effect induced by subtle compositional changes on intermetallic energy transfer, and thus on the resulting photophysical properties, is demonstrated. This strategy can be widely implemented to create a large library of highly complex, difficult‐to‐counterfeit optical tags.

Deneff, Jacob I.↗
DOE OSTI2020

Luminescent Properties of DOBDC Containing MOFs: The Role of Free Hydroxyls

A novel metal–organic framework (MOF), Mn-DOBDC, has been synthesized in an effort to investigate the role of both the metal center and presence of free linker hydroxyls on the luminescent properties of DOBDC (2,5-dihydroxyterephthalic acid) containing MOFs. Co-MOF-74, RE-DOBDC (RE–Eu and Tb), and Mn-DOBDC have been synthesized and analyzed by powder X-ray diffraction (PXRD) and the fluorescent properties probed by UV–Vis spectroscopy and density functional theory (DFT). Mn-DOBDC has been synthesized by a new method involving a concurrent facile reflux synthesis and slow crystallization, resulting in yellow single crystals in monoclinic space group C2/c. Mn-DOBDC was further analyzed by single-crystal X-ray diffraction (SCXRD), scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS), and photoluminescent emission. Results indicate that the luminescent properties of the DOBDC linker are transferred to the three-dimensional structures of both the RE-DOBDC and Mn-DOBDC, which contain free hydroxyls on the linker. In Co-MOF-74 however, luminescence is quenched in the solid state due to binding of the phenolic hydroxyls within the MOF structure. Finally, Mn-DOBDC exhibits a ligand-based tunable emission that can be controlled in solution by the use of different solvents.

36 MATERIALS SCIENCE↗