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1. X-ray absorption spectroscopy insights on the structure anisotropy and charge transfer in Chevrel Phase chalcogenides

   https://doi.org/10.1039/d1cp04851a  

   Hyler, Forrest P. ; Wuille Bille, Brian A. ; Ortíz-Rodríguez, Jessica C. ; Sanz-Matias, Ana ; Roychoudhury, Subhayan ; Perryman, Joseph T. ; Patridge, Christopher J. ; Singstock, Nicholas R. ; Musgrave, Charles B. ; Prendergast, David ; et al ( July 2022 , Physical Chemistry Chemical Physics)

   The electronic structure and local coordination of binary (Mo 6 T 8 ) and ternary Chevrel Phases (M x Mo 6 T 8 ) are investigated for a range of metal intercalant and chalcogen compositions. We evaluate differences in the Mo L 3 -edge and K-edge X-ray absorption near edge structure across the suite of chalcogenides M x Mo 6 T 8 (M = Cu, Ni, x = 1–2, T = S, Se, Te), quantifying the effect of compositional and structural modification on electronic structure. Furthermore, we highlight the expansion, contraction, and anisotropy of Mo 6 clusters within these Chevrel Phase frameworks through extended X-ray absorption fine structure analysis. Our results show that metal-to-cluster charge transfer upon intercalation is dominated by the chalcogen acceptors, evidenced by significant changes in their respective X-ray absorption spectra in comparison to relatively unaffected Mo cations. These results explain the effects of metal intercalation on the electronic and local structure of Chevrel Phases across various chalcogen compositions, and aid in rationalizing electron distribution within the structure. 

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2. Structural and electronic switching of a single crystal 2D metal-organic framework prepared by chemical vapor deposition

   https://doi.org/10.1038/s41467-020-19220-y  

   Claire, F. James ; Solomos, Marina A. ; Kim, Jungkil ; Wang, Gaoqiang ; Siegler, Maxime A. ; Crommie, Michael F. ; Kempa, Thomas J. ( November 2020 , Nature Communications)

   The incorporation of metal-organic frameworks into advanced devices remains a desirable goal, but progress is hindered by difficulties in preparing large crystalline metal-organic framework films with suitable electronic performance. We demonstrate the direct growth of large-area, high quality, and phase pure single metal-organic framework crystals through chemical vapor deposition of a dimolybdenum paddlewheel precursor, Mo₂(INA)₄. These exceptionally uniform, high quality crystals cover areas up to 8600 µm²and can be grown down to thicknesses of 30 nm. Moreover, scanning tunneling microscopy indicates that the Mo₂(INA)₄clusters assemble into a two-dimensional, single-layer framework. Devices are readily fabricated from single vapor-phase grown crystals and exhibit reversible 8-fold changes in conductivity upon illumination at modest powers. Moreover, we identify vapor-induced single crystal transitions that are reversible and responsible for 30-fold changes in conductivity of the metal-organic framework as monitored by in situ device measurements. Gas-phase methods, including chemical vapor deposition, show broader promise for the preparation of high-quality molecular frameworks, and may enable their integration into devices, including detectors and actuators.

    

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3. Quantitative Analysis of Doping-Induced Polarons and Charge-Transfer Complexes of Poly(3-hexylthiophene) in Solution

   https://doi.org/10.1021/acs.jpcb.0c03517  

   Arvind, Malavika ; Tait, Claudia ; Guerrini, Michele ; Krumland, Jannis ; Valencia, Ana Maria ; Cocchi, Caterina ; Mansour, Ahmed E. ; Koch, Norbert ; Barlow, Stephen ; Marder, Seth R. ; et al ( June 2020 , The Journal of Physical Chemistry B)

   The mechanism and the nature of the species formed by molecular doping of the model polymer poly(3-hexylthiophene) (P3HT) in its regioregular (rre-) and regiorandom (rra-) forms in solution are investigated for three different dopants: the prototypical π-electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), the strong Lewis acid tris(pentafluorophenyl)borane (BCF), and the strongly oxidizing complex molybdenum tris[1-(methoxycarbonyl)-2-(trifluoromethyl)-ethane-1,2-dithiolene] (Mo(tfd-CO2Me)3). In a combined optical and electron paramagnetic resonance study, we show that the doping of rreP3HT in solution occurs by integer charge transfer, resulting in the formation of P3HT radical cations (polarons) for all the dopants considered here. Remarkably, despite the different chemical nature of the dopants and dopant-polymer interaction, the formed polarons exhibit essentially identical optical absorption spectra. The situation is very different for the doping of rraP3HT, where we observe the formation of a charge-transfer complex with F4TCNQ and formation of a “localized” P3HT polaron on non-aggregated chains upon doping with BCF, while there is no indication of dopant-induced species in case of Mo(tfd-CO2Me)3. We estimate the ionization efficiency of the respective dopants for the two polymers in solution and report the molar extinction coefficient spectra of the three different species. Finally, we observe increased spin delocalization in regioregular compared to regiorandom P3HT by electron nuclear double resonance, suggesting that the ability of the charge to delocalize on aggregates of planarized polymer backbones plays a significant role in determining the doping mechanism. 

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4. Charge transport in individual short base stacked single-stranded RNA molecules

   https://doi.org/10.1038/s41598-023-46263-0  

   Chandra, Subrata ; Williams, Ajoke ; Maksudov, Farkhad ; Kliuchnikov, Evgenii ; Pattiya Arachchillage, Keshani G. G. ; Piscitelli, Patrick ; Castillo, Aderlyn ; Marx, Kenneth A. ; Barsegov, Valeri ; Artes Vivancos, Juan M. ( November 2023 , Scientific Reports)

   Charge transport in biomolecules is crucial for many biological and technological applications, including biomolecular electronics devices and biosensors. RNA has become the focus of research because of its importance in biomedicine, but its charge transport properties are not well understood. Here, we use the Scanning Tunneling Microscopy-assisted molecular break junction method to measure the electrical conductance of particular 5-base and 10-base single-stranded (ss) RNA sequences capable of base stacking. These ssRNA sequences show single-molecule conductance values around$$10^{-3}G_0$$${10}^{-3}{G}_0$($$G_0= 2e^2/h$$$G_0=2e^2/h$), while equivalent-length ssDNAs result in featureless conductance histograms. Circular dichroism (CD) spectra and MD simulations reveal the existence of extended ssRNA conformations versus folded ssDNA conformations, consistent with their different electrical behaviors. Computational molecular modeling and Machine Learning-assisted interpretation of CD data helped us to disentangle the structural and electronic factors underlying CT, thus explaining the observed electrical behavior differences. RNA with a measurable conductance corresponds to sequences with overall extended base-stacking stabilized conformations characterized by lower HOMO energy levels delocalized over a base-stacking mediating CT pathway. In contrast, DNA and a control RNA sequence without significant base-stacking tend to form closed structures and thus are incapable of efficient CT.

    

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5. Enhanced Charge Transport and Stability Conferred by Iron(III)‐Coordination in a Conjugated Polymer Thin‐Film Transistors

   https://doi.org/10.1002/aelm.201800239  

   Wu, Hung‐Chin ; Rondeau‐Gagné, Simon ; Chiu, Yu‐Cheng ; Lissel, Franziska ; To, John W. F. ; Tsao, Yuchi ; Oh, Jin Young ; Tang, Bohan ; Chen, Wen‐Chang ; Tok, Jeffery B. ‐H. ; et al ( June 2018 , Advanced Electronic Materials)

   A high performance diketopyrrolopyrrole (DPP)–based semiconducting polymer is modified with ligands to enable metal coordination, and its subsequent effect as field‐effect transistors is investigated. In specific, pyridine‐2,6‐dicarboxamide (PDCA) units are incorporated in a DPP–based polymer backbone with a content from 0 to 30 mol%, and the resulting polymers are then mixed with Fe(II) ions. The coordination and spontaneous oxidation converts Fe(II) to Fe(III) ions to result in Fe(III)‐containing metallopolymers. The resulting metallopolymers are observed to show good solubility in organic solvents and can be easily processed as thin films. The charge transport characteristics are subsequently investigated through the fabrication of field–effect transistor devices, in which an enhanced charge carrier mobility with the Fe(III)‐containing metallopolymers is observed. In specific, an almost twofold improvement in the charge carrier mobility is obtained for the 20% PDCA‐containing polymer after Fe coordination (from 0.96 to 1.84 cm²V⁻¹s⁻¹). Furthermore, the operation stability of the metallopolymer‐based devices is found to be significantly improved with low bias stress. Its superior electrical characteristics are attributed to the doping effect of the Fe ions. This study indicates that incorporation of appropriate metallic ions to polymer presents a viable approach to enhance the performance of polymer–based transistor devices.

    

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