Triplet State Baird-Aromaticity in Macrocycles: Scope, Limitations and Complications

The aromaticity of cyclic 4np-electron molecules in their first pp* triplet state (T1), labelled Baird-aromaticity, has gained growing attention in the last decade. Here we explore computationally the limitations of T1 state Baird-aromaticity in macrocyclic compounds, [n]CM’s, which are cyclic oligomers of four different monocycles (M = para-phenylene (PP), 2,5-linked furan (FU), 1,4-linked cyclohexa-1,3-diene (CHD), and 1,4-linked cyclopentadiene (CPD)). We strive for conclusions that are general for various DFT functionals, although for macrocycles with up to 20 p-electrons in their main conjugation paths we find that for their T1 states single-point energies at both canonical UCCSD(T) and approximative DLPNO-UCCSD(T) levels are lowest when based on UB3LYP over UM06-2X and UCAM-B3LYP geometries. This finding is in contrast to what has earlier been observed for the electronic ground state of expanded porphyrins. Yet, irrespective of functional, macrocycles with 2,5-linked furans ([n]CFU’s) retain Baird-aromaticity until larger n than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a 3[n]CFU with a specific n is more strongly Baird-aromatic than the analogous 3[n]CPP while the magnetic indices tell the opposite. To construct large T1 state Baird-aromatic [n]CM’s the design should be such that the T1 state Baird-aromaticity of the macrocyclic perimeter dominates over a situation with local closed-shell Hückel-aromaticity of one or a few monocycles and semi-localized triplet diradical character. Monomers with lower Hückel-aromaticity in S0 than benzene (e.g., furan) that do not impose steric congestion are preferred. Structural confinement imposed by, e.g., methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T1 state aromaticity we reveal the analogy to the Hückel-aromaticity of the corresponding closed-shell dications, yet, observe stronger Hückel-aromaticity in the macrocyclic dications than Baird-aromaticity in the T1 states of the neutral macrocycles.

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Triplet State Baird-Aromaticity in Macrocycles: Scope, Limitations and Complications

10.26434/chemrxiv.13029359 ◽

2020 ◽

Author(s):

Rabia Ayub ◽

Ouissam El Bakouri ◽

Joshua R. Smith ◽

Kjell Jorner ◽

Henrik Ottosson

Keyword(s):

Triplet State ◽

Ground State ◽

Single Point ◽

Closed Shell ◽

The Other ◽

Macrocyclic Compounds ◽

Expanded Porphyrins ◽

Diradical Character ◽

Cyclic Oligomers ◽

Electronic Ground

The aromaticity of cyclic 4np-electron molecules in their first pp* triplet state (T1), labelled Baird-aromaticity, has gained growing attention in the last decade. Here we explore computationally the limitations of T1 state Baird-aromaticity in macrocyclic compounds, [n]CM’s, which are cyclic oligomers of four different monocycles (M = para-phenylene (PP), 2,5-linked furan (FU), 1,4-linked cyclohexa-1,3-diene (CHD), and 1,4-linked cyclopentadiene (CPD)). We strive for conclusions that are general for various DFT functionals, although for macrocycles with up to 20 p-electrons in their main conjugation paths we find that for their T1 states single-point energies at both canonical UCCSD(T) and approximative DLPNO-UCCSD(T) levels are lowest when based on UB3LYP over UM06-2X and UCAM-B3LYP geometries. This finding is in contrast to what has earlier been observed for the electronic ground state of expanded porphyrins. Yet, irrespective of functional, macrocycles with 2,5-linked furans ([n]CFU’s) retain Baird-aromaticity until larger n than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a 3[n]CFU with a specific n is more strongly Baird-aromatic than the analogous 3[n]CPP while the magnetic indices tell the opposite. To construct large T1 state Baird-aromatic [n]CM’s the design should be such that the T1 state Baird-aromaticity of the macrocyclic perimeter dominates over a situation with local closed-shell Hückel-aromaticity of one or a few monocycles and semi-localized triplet diradical character. Monomers with lower Hückel-aromaticity in S0 than benzene (e.g., furan) that do not impose steric congestion are preferred. Structural confinement imposed by, e.g., methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T1 state aromaticity we reveal the analogy to the Hückel-aromaticity of the corresponding closed-shell dications, yet, observe stronger Hückel-aromaticity in the macrocyclic dications than Baird-aromaticity in the T1 states of the neutral macrocycles.

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Sulfamoyl nitrenes: singlet or triplet ground state?

Chemical Communications ◽

10.1039/c8cc03278e ◽

2018 ◽

Vol 54 (48) ◽

pp. 6136-6139 ◽

Cited By ~ 5

Author(s):

Yan Lu ◽

Hongmin Li ◽

Manabu Abe ◽

Didier Bégué ◽

Huabin Wan ◽

...

Keyword(s):

Triplet State ◽

Ground State ◽

Singlet State ◽

Minimum Energy ◽

Closed Shell ◽

Low Energy ◽

Energy Minimum ◽

Triplet Ground State ◽

Crossing Point

Two prototypical sulfamoyl nitrenes R2NS(O)2–N (R = H and Me) in the triplet state were generated via the closed-shell singlet state by passing a low-energy minimum energy crossing point (MECP).

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Simplified Non-Empirical Unrestricted Hartree-Fock Approximation (SUHF) for the Calculation of Electronic Ground State Properties of Molecules with Closed and Open Valence Shells. I. Method

Zeitschrift für Naturforschung A ◽

10.1515/zna-1993-0714 ◽

1993 ◽

Vol 48 (7) ◽

pp. 829-833

Author(s):

Wolfhard Koch

Keyword(s):

Electron Correlation ◽

Ground State ◽

Atomic Orbital ◽

Closed Shell ◽

Open Shell ◽

Polyatomic Molecules ◽

Correlation Effects ◽

Hartree Fock ◽

Electron Correlation Effects ◽

Electronic Ground

Abstract Focusing on relative stabilities of electronic states with different spin multiplicities of polyatomic molecules, a simplified unrestricted Hartree-Fock (SUHF) procedure is described. Using different orbitals for different spins (DODS), electron correlation effects of both closed-shell and open-shell systems are expected to be taken into account in the simplest way. While working within a symmetrically orthogonalized (Löwdin) basis we make use of the NDDO approximation (neglect of diatomic differential overlap) concerning the evaluation of electron repulsion and nuclear attraction integrals. Originally, a locally orthogonalized all-electron atomic orbital set of Slater type is considered. The approximation method is completely non-empirical. Rotational invariance is fully retained.

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Noble gas hydrides in the triplet state: HNgCCO+ (Ng = He, Ne, Ar, Kr, and Xe)

Physical Chemistry Chemical Physics ◽

10.1039/c8cp03516d ◽

2018 ◽

Vol 20 (30) ◽

pp. 20270-20279 ◽

Cited By ~ 6

Author(s):

Ayan Ghosh ◽

Arijit Gupta ◽

Rishabh Gupta ◽

Tapan K. Ghanty

Keyword(s):

Triplet State ◽

Ab Initio ◽

Ground State ◽

Noble Gas ◽

Electronic Ground State ◽

Electronic Ground

Existence of noble gas-inserted ketenyl cations, HNgCCO+ (Ng = He, Ne, Ar, Kr, and Xe) species, with a triplet electronic ground state is predicted through ab initio calculations.

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Anti-ohmic Nanoconductors: Myth, Reality and Promise

10.26434/chemrxiv-2021-bf1nx ◽

2021 ◽

Author(s):

Ashima Bajaj ◽

Md. Ehesan Ali

Keyword(s):

Symmetry Breaking ◽

Ground State ◽

Closed Shell ◽

Open Shell ◽

Molecular Junctions ◽

Spatial Symmetry ◽

New Family ◽

Diradical Character ◽

Classical Behavior

The recent accomplishments in the design of molecular nanowires characterised by an increasing conductance with length has embarked the origin of extraordinary new family of molecular junctions referred to as "anti-ohmic" wires. Herein, this highly desirable, non-classical behavior, has been examined for the longer enough molecules exhibiting pronounced diradical character in their ground state within the unrestricted DFT formalism with spin and spatial symmetry breaking. We demonstrate that highly conjugated acenes signals higher resistance in open-shell singlet (OSS) configuration as compared to their closed-shell counterparts. This anomaly has been further put to proof for experimentally certified cumulene wires, which reveals phenomenal modulation in the transport characteristics such that an increasing conductance is observed in closed-shell limit, while higher cumulenes in OSS ground state yields a regular decay of conductance.

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MILLIMETER-WAVE SPECTROSCOPY OF KO: ESTABLISHING THE ELECTRONIC GROUND STATE

Proceedings of the 73rd International Symposium on Molecular Spectroscopy ◽

10.15278/isms.2018.wd05 ◽

2018 ◽

Author(s):

Mark Burton ◽

Lucy Ziurys ◽

Matthew Bucchino ◽

Phillip Sheridan ◽

Benjamin Russ

Keyword(s):

Millimeter Wave ◽

Ground State ◽

Electronic Ground State ◽

Millimeter Wave Spectroscopy ◽

Electronic Ground

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THE ELECTRONIC GROUND STATE OF THE NITRATE RADICAL: A DECADE OF CONTROVERSY

Proceedings of the 72nd International Symposium on Molecular Spectroscopy ◽

10.15278/isms.2017.mg01 ◽

2017 ◽

Author(s):

John Stanton

Keyword(s):

Ground State ◽

Electronic Ground State ◽

Nitrate Radical ◽

Electronic Ground

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Ground state and stability of the fractional plateau phase in metallic Shastry–Sutherland system TmB4

Scientific Reports ◽

10.1038/s41598-021-86353-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Matúš Orendáč ◽

Slavomír Gabáni ◽

Pavol Farkašovský ◽

Emil Gažo ◽

Jozef Kačmarčík ◽

...

Keyword(s):

Magnetic Field ◽

Phase Diagram ◽

Ground State ◽

Constant Magnetic Field ◽

Paramagnetic Phase ◽

The Other ◽

Zero Field ◽

Plateau Phase ◽

Low Field ◽

Zero Field Cooling

AbstractWe present a study of the ground state and stability of the fractional plateau phase (FPP) with M/Msat = 1/8 in the metallic Shastry–Sutherland system TmB4. Magnetization (M) measurements show that the FPP states are thermodynamically stable when the sample is cooled in constant magnetic field from the paramagnetic phase to the ordered one at 2 K. On the other hand, after zero-field cooling and subsequent magnetization these states appear to be of dynamic origin. In this case the FPP states are closely associated with the half plateau phase (HPP, M/Msat = ½), mediate the HPP to the low-field antiferromagnetic (AF) phase and depend on the thermodynamic history. Thus, in the same place of the phase diagram both, the stable and the metastable (dynamic) fractional plateau (FP) states, can be observed, depending on the way they are reached. In case of metastable FP states thermodynamic paths are identified that lead to very flat fractional plateaus in the FPP. Moreover, with a further decrease of magnetic field also the low-field AF phase becomes influenced and exhibits a plateau of the order of 1/1000 Msat.

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