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1. Exploring the Influence of Chalcogens on Metalloporphyrins: A DFT Study

   https://doi.org/10.3390/molecules30112254  

   Bashir, Beenish; Clayborne, Andre Z (May 2025, Molecules)

   Metalloporphyrins and porphyrins (MPs) have garnered increasing attention as potential candidates for molecular-based electronic devices and single-atom catalysis. Recent studies have found that electronic structure calculations are important factors in controlling the performance of MPs as building blocks for single-molecule devices. Our study investigates metalloporphyrins with central 3d-metals from Sc to Cu and chalcogen containing anchoring groups such as -SH, -SeH, and -TeH substituted at the meso-position of the porphyrin rings. We carried out Density Function Theory (DFT)-based calculations to determine the ground state geometry, spin multiplicity, spatial distribution of the molecular orbitals, and electronic structure descriptors to gain insights into the reactivity trends and possible impact on factors influencing electron transport properties. The results suggest that the central metal shapes the spin multiplicity, while variations between sulfur, selenium, and tellurium play a role in charge distribution. This study provides insights into how the selection of the central metal and control of spin channels influence the electronic structure and reactivity of metalloporphyrin molecules. The knowledge provided here can play a role in the design of porphyrin-based molecular materials for diverse applications in molecular junctions, catalysis, photovoltaics, and sensing. 

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2. Computational investigation of structural, electronic, and spectroscopic properties of Ni and Zn metalloporphyrins with varying anchoring groups

   https://doi.org/10.1063/5.0191858  

   Bashir, Beenish; Alotaibi, Maha_M; Clayborne, Andre_Z (April 2024, The Journal of Chemical Physics)

   Porphyrins are prime candidates for a host of molecular electronics applications. Understanding the electronic structure and the role of anchoring groups on porphyrins is a prerequisite for researchers to comprehend their role in molecular devices at the molecular junction interface. Here, we use the density functional theory approach to investigate the influence of anchoring groups on Ni and Zn diphenylporphyrin molecules. The changes in geometry, electronic structure, and electronic descriptors were evaluated. There are minimal changes observed in geometry when changing the metal from Ni to Zn and the anchoring group. However, we find that the distribution of electron density changes when changing the anchoring group in the highest occupied and lowest unoccupied molecular orbitals. This has a direct effect on electronic descriptors such as global hardness, softness, and electrophilicity. Additionally, the optical spectra of both Ni and Zn diphenylporphyrin molecules exhibit either blue or red shifts when changing the anchoring group. These results indicate the importance of the anchoring group on the electronic structure and optical properties of porphyrin molecules. 

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3. A Hybrid Pulsed Laser Deposition Approach to Grow Thin Films of Chalcogenides

   https://doi.org/10.1002/adma.202312620  

   Surendran, Mythili; Singh, Shantanu; Chen, Huandong; Wu, Claire; Avishai, Amir; Shao, Yu‐Tsun; Ravichandran, Jayakanth (February 2024, Advanced Materials)

   Abstract Vapor‐pressure mismatched materials such as transition metal chalcogenides have emerged as electronic, photonic, and quantum materials with scientific and technological importance. However, epitaxial growth of vapor‐pressure mismatched materials are challenging due to differences in the reactivity, sticking coefficient, and surface adatom mobility of the mismatched species constituting the material, especially sulfur containing compounds. Here, a novel approach is reported to grow chalcogenides—hybrid pulsed laser deposition—wherein an organosulfur precursor is used as a sulfur source in conjunction with pulsed laser deposition to regulate the stoichiometry of the deposited films. Epitaxial or textured thin films of sulfides with variety of structure and chemistry such as alkaline metal chalcogenides, main group chalcogenides, transition metal chalcogenides, and chalcogenide perovskites are demonstrated, and structural characterization reveal improvement in thin film crystallinity, and surface and interface roughness compared to the state‐of‐the‐art. The growth method can be broadened to other vapor‐pressure mismatched chalcogenides such as selenides and tellurides. This work opens up opportunities for broader epitaxial growth of chalcogenides, especially sulfide‐based thin film technological applications. 

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4. Solvent-Mediated Modulation of the Au–S Bond in Dithiol Molecular Junctions

   https://doi.org/10.1021/acs.nanolett.3c04058  

   Dalmieda, Johnson; Shi, Wanzhuo; Li, Liang; Venkataraman, Latha (January 2024, Nano Letters)

   NA (Ed.)

   Gold-dithiol molecular junctions have been studied both experimentally and theoretically. However, the nature of the gold-thiolate bond as it relates to the solvent has been seldom investigated. It is known that solvents can impact the electronic structure of single molecule junctions, but the correlation between the solvent and dithiol-linked single-molecule junction conductance is not well understood. We study molecular junctions formed with thiol terminated phenylenes from both 1-chloronaphthalene and 1-bromonaphthalene solutions. We find that the most probable conductance and the distribution of conductances are both affected by the solvent. First-principles calculations show that junction conductance depends on the binding configurations (adatom, atop, bridge) of the thiolate on the Au surface as has been shown previously. More importantly, we find that brominated solvents can restrict the binding of thiols to specific Au sites. This mechanism offers new insight into the effects of the solvent environment on covalent bonding in molecular junctions. 

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5. Rectification in Molecular Tunneling Junctions Based on Alkanethiolates with Bipyridine–Metal Complexes

   https://doi.org/doi.org/10.1021/jacs.0c12641  

   J. Park, L. Belding (January 2021, Journal of the American Chemical Society)

   null (Ed.)

   This paper addresses the mechanism for rectification in molecular tunneling junctions based on alkanethiolates terminated by a bipyridine group complexed with a metal ion, that is, having the structure AuTS-S(CH2)11BIPY-MCl2 (where M = Co or Cu) with a eutectic indium–gallium alloy top contact (EGaIn, 75.5% Ga 24.5% In). Here, AuTS-S(CH2)11BIPY is a self-assembled monolayer (SAM) of an alkanethiolate with 4-methyl-2,2′-bipyridine (BIPY) head groups, on template-stripped gold (AuTS). When the SAM is exposed to cobalt(II) chloride, SAMs of the form AuTS-S(CH2)11BIPY-CoCl2 rectify current with a rectification ratio of r+ = 82.0 at ±1.0 V. The rectification, however, disappears (r+ = 1.0) when the SAM is exposed to copper(II) chloride instead of cobalt. We draw the following conclusions from our experimental results: (i) AuTS-S(CH2)11BIPY-CoCl2 junctions rectify current because only at positive bias (+1.0 V) is there an accessible molecular orbital (the LUMO) on the BIPY-CoCl2 moiety, while at negative bias (−1.0 V), neither the energy level of the HOMO or the LUMO lies between the Fermi levels of the electrodes. (ii) AuTS-S(CH2)11BIPY-CuCl2 junctions do not rectify current because there is an accessible molecular orbital on the BIPY-CuCl2 moiety at both negative and positive bias (the HOMO is accessible at negative bias, and the LUMO is accessible at positive bias). The difference in accessibility of the HOMO levels at −1.0 V causes charge transfer—at negative bias—to take place via Fowler–Nordheim tunneling in BIPY-CoCl2 junctions, and via direct tunneling in BIPY-CuCl2 junctions. This difference in tunneling mechanism at negative bias is the origin of the difference in rectification ratio between BIPY-CoCl2 and BIPY-CuCl2 junctions. 

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