arXiv subjects

Shadi Fatayer

Publications and source records attributed to Shadi Fatayer.

7 recordsLinked to original sources

arXiv2024

Observation of SOMO-HOMO inversion in a polycyclic conjugated hydrocarbon

We report the generation of a non-benzenoid polycyclic conjugated hydrocarbon, which consists of a biphenyl moiety substituted by indenyl units at the 4,4' positions, on ultra-thin sodium chloride films by tip-induced chemistry. Single-molecule characterization by scanning tunneling and atomic force microscopy reveals an open-shell biradical ground state, with a peculiar electronic configuration wherein the singly-occupied molecular orbitals (SOMOs) are lower in energy than the highest occupied molecular orbital (HOMO).

cond-mat.mes-hall↗

arXiv2023

Bistability between $\pi$-diradical open-shell and closed-shell states in indeno[1,2-a]fluorene

Indenofluorenes are non-benzenoid conjugated hydrocarbons that have received great interest owing to their unusual electronic structure and potential applications in non-linear optics and photovoltaics. Here, we report the generation of unsubstituted indeno[1,2-a]fluorene, the final and yet unreported parent indenofluorene isomer, on various surfaces by cleavage of two C-H bonds in 7,12-dihydroindeno[1,2-a]fluorene through voltage pulses applied by the tip of a combined scanning tunneling microscope and atomic force microscope. On bilayer NaCl on Au(111), indeno[1,2-a]fluorene is in the neutral charge state, while it exhibits charge bistability between neutral and anionic states on the lower work function surfaces of bilayer NaCl on Ag(111) and Cu(111). In the neutral state, indeno[1,2-a]fluorene exhibits either of two ground states: an open-shell pi-diradical state, predicted to be a triplet by density functional and multireference many-body perturbation theory calculations, or a closed-shell state with a para-quinodimethane moiety in the as-indacene core. Switching between open- and closed-shell states of a single molecule is observed by changing its adsorption site on NaCl.

cond-mat.mes-hall↗

arXiv2022

Selectivity in single-molecule reactions by tip-induced redox chemistry

Controlling selectivity of reactions is a quest in chemistry. Here, we demonstrate reversible and selective bond formation and dissociation promoted by tip-induced reduction-oxidation reactions on a surface. Molecular rearrangements leading to different constitutional isomers are selected by the polarity and magnitude of applied voltage pulses from the tip of a combined scanning tunneling and atomic force microscope. Characterization of voltage dependence of the reactions and determination of reaction rates demonstrate selectivity in constitutional isomerization reactions and provide insight into the underlying mechanisms. With support of density functional theory calculations, we find that the energy landscape of the isomers in different charge states is important to rationalize the selectivity. Tip-induced selective single-molecule reactions increase our understanding of redox chemistry and could lead to novel molecular machines.

physics.chem-ph↗

arXiv2022

Non-benzenoid high-spin polycyclic hydrocarbons generated by atom manipulation

We report the on-surface synthesis of a non-benzenoid triradical through dehydrogenation of truxene (C27H18) on coinage metal and insulator surfaces. Voltage pulses applied via the tip of a combined scanning tunneling microscope/atomic force microscope were used to cleave individual C-H bonds in truxene. The resultant final product truxene-5,10,15-triyl (1) was characterized at the single-molecule scale using a combination of atomic force microscopy, scanning tunneling microscopy and scanning tunneling spectroscopy. Our analyses show that 1 retains its open-shell quartet ground state, predicted by density functional theory, on a two monolayer-thick NaCl layer on a Cu(111) surface. We image the frontier orbital densities of 1 and confirm that they correspond to spin-split singly occupied molecular orbitals. Through our synthetic strategy, we also isolate two reactive intermediates toward the synthesis of 1 - derivatives of fluorenyl radical and indeno[1,2-a]fluorene, with predicted spin-doublet and spin-triplet ground states, respectively. Our results should have bearings on the synthesis of non-benzenoid high-spin polycyclic frameworks with magnetism beyond Lieb's theorem.

cond-mat.mes-hall↗

arXiv2020

Probing molecular excited states by atomic force microscopy

By employing single charge injections with an atomic force microscope, we investigated redox reactions of a molecule on a multilayer insulating film. First, we charged the molecule positively by attaching a single hole. Then we neutralized it by attaching an electron and observed three channels for the neutralization. We rationalize that the three channels correspond to transitions to the neutral ground state, to the lowest energy triplet excited states and to the lowest energy singlet excited states. By single-electron tunneling spectroscopy we measured the energy differences between the transitions obtaining triplet and singlet excited state energies. The experimental values are compared with density functional theory calculations of the excited state energies. Our results show that molecules in excited states can be prepared and that energies of optical gaps can be quantified by controlled single-charge injections. Our work demonstrates the access to, and provides insight into, ubiquitous electron-attachment processes related to excited-state transitions important in electron transfer and molecular optoelectronics phenomena on surfaces.

cond-mat.mes-hall↗

arXiv2020

Intramolecular coupling of terminal alkynes by atom manipulation

Glaser-like coupling of terminal alkynes by thermal activation is extensively used in on-surface chemistry. Here we demonstrate an intramolecular version of this reaction performed by atom manipulation. We used voltage pulses from the tip to trigger a Glaser-like coupling between terminal alkyne carbons within a custom synthesized precursor molecule adsorbed on bilayer NaCl on Cu(111). Different conformations of the precursor molecule and the product were characterized by molecular structure elucidation with atomic force microscopy and orbital density mapping with scanning tunneling microscopy, accompanied by density functional theory calculations. We revealed partially dehydrogenated intermediates providing insight into the reaction pathway.

physics.chem-ph↗

arXiv2019

Molecular structure elucidation with charge-state control

The charge state of a molecule governs its physicochemical properties, such as conformation, reactivity and aromaticity, with implications for on-surface synthesis, catalysis, photo conversion and applications in molecular electronics. On insulating, multilayer NaCl films we control the charge state of organic molecules and resolve their structures in neutral, cationic, anionic and dianionic states by atomic force microscopy, obtaining atomic resolution and bond-order discrimination using CO functionalized tips. We detect changes in conformation, adsorption geometry and bond-order relations for azobenzene, tetracyanoquinodimethane and pentacene in multiple charge states. Moreover, for porphine we investigate the charge-state-dependent change of aromaticity and conjugation pathway in the macrocycle. This work opens the way to studying chemical-structural changes of individual molecules for a wide range of charge states.

cond-mat.mes-hall↗