Fluoreno[2,1-a]fluorene: an ortho-naphthoquinodimethane-based system with partial diradical character

2019 ◽  
Vol 55 (94) ◽  
pp. 14186-14189 ◽  
Author(s):  
Allison S. Hacker ◽  
Mauricio Pavano ◽  
James E. Wood ◽  
Hannah Hashimoto ◽  
Kyle M. D’Ambrosio ◽  
...  
Keyword(s):  
Closed Shell ◽  
Intermediate Case ◽  
Diradical Character

An ortho-naphtho diradical! Quinoidal forms in para- and meta-patterns lie at the extremes for closed-shell and diradical forms in fluorenofluorenes, respectively. ortho-Conjugation gives an intermediate case with partial diradical character.

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

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

<p>The aromaticity of cyclic 4<i>n</i>p-electron molecules in their first pp* triplet state (T<sub>1</sub>), labelled Baird-aromaticity, has gained growing attention in the last decade. Here we explore computationally the limitations of T<sub>1</sub> state Baird-aromaticity in macrocyclic compounds, <b>[<i>n</i>]CM</b>’s, which are cyclic oligomers of four different monocycles (M = <i>para</i>-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 T<sub>1</sub> 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 (<b>[<i>n</i>]CFU</b>’s) retain Baird-aromaticity until larger <i>n</i> than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a <b><sup>3</sup>[<i>n</i>]CFU</b> with a specific <i>n</i> is more strongly Baird-aromatic than the analogous <b><sup>3</sup>[<i>n</i>]CPP</b> while the magnetic indices tell the opposite. To construct large T<sub>1</sub> state Baird-aromatic <b>[<i>n</i>]CM</b>’s the design should be such that the T<sub>1</sub> 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 S<sub>0</sub> than benzene (<i>e.g.</i>, furan) that do not impose steric congestion are preferred. Structural confinement imposed by, <i>e.g.</i>, methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T<sub>1</sub> 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 T<sub>1</sub> states of the neutral macrocycles. </p>

scholarly journals Evolution of the electronic structure in open-shell donor-acceptor organic semiconductors

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Zhongxin Chen ◽  
Wenqiang Li ◽  
Md Abdus Sabuj ◽  
Yuan Li ◽  
Weiya Zhu ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Organic Semiconductors ◽  
High Performance ◽  
Closed Shell ◽  
Open Shell ◽  
Ground State Structure ◽  
Structure Property ◽  
System A ◽  
Diradical Character ◽  
Donor Acceptor

AbstractMost organic semiconductors have closed-shell electronic structures, however, studies have revealed open-shell character emanating from design paradigms such as narrowing the bandgap and controlling the quinoidal-aromatic resonance of the π-system. A fundamental challenge is understanding and identifying the molecular and electronic basis for the transition from a closed- to open-shell electronic structure and connecting the physicochemical properties with (opto)electronic functionality. Here, we report donor-acceptor organic semiconductors comprised of diketopyrrolopyrrole and naphthobisthiadiazole acceptors and various electron-rich donors commonly utilized in constructing high-performance organic semiconductors. Nuclear magnetic resonance, electron spin resonance, magnetic susceptibility measurements, single-crystal X-ray studies, and computational investigations connect the bandgap, π-extension, structural, and electronic features with the emergence of various degrees of diradical character. This work systematically demonstrates the widespread diradical character in the classical donor-acceptor organic semiconductors and provides distinctive insights into their ground state structure-property relationship.

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

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

<p>The aromaticity of cyclic 4<i>n</i>p-electron molecules in their first pp* triplet state (T<sub>1</sub>), labelled Baird-aromaticity, has gained growing attention in the last decade. Here we explore computationally the limitations of T<sub>1</sub> state Baird-aromaticity in macrocyclic compounds, <b>[<i>n</i>]CM</b>’s, which are cyclic oligomers of four different monocycles (M = <i>para</i>-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 T<sub>1</sub> 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 (<b>[<i>n</i>]CFU</b>’s) retain Baird-aromaticity until larger <i>n</i> than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a <b><sup>3</sup>[<i>n</i>]CFU</b> with a specific <i>n</i> is more strongly Baird-aromatic than the analogous <b><sup>3</sup>[<i>n</i>]CPP</b> while the magnetic indices tell the opposite. To construct large T<sub>1</sub> state Baird-aromatic <b>[<i>n</i>]CM</b>’s the design should be such that the T<sub>1</sub> 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 S<sub>0</sub> than benzene (<i>e.g.</i>, furan) that do not impose steric congestion are preferred. Structural confinement imposed by, <i>e.g.</i>, methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T<sub>1</sub> 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 T<sub>1</sub> states of the neutral macrocycles. </p>

Ca–Ca interaction in inverse sandwich Ca–C8H8–Ca

2015 ◽  
Vol 44 (1) ◽  
pp. 345-350 ◽  
Author(s):  
Nan-nan Liu ◽  
Si-meng Gao ◽  
Yi-hong Ding
Keyword(s):  
Dimethyl Ether ◽  
Closed Shell ◽  
Open Shell ◽  
Diradical Character

The inverse sandwich Ca–C8H8–Ca is predicted to be open-shell singlet Ca–C8H8–Ca. The singlet diradical character is caused by the C8H8 ligand preventing the spin-paired electrons of different calcium atoms from forming Ca–Ca bonds. A direct Ca–Ca bond is favorable in closed-shell singlet (DME)3Ca–C8H8–Ca(DME)3, because dimethyl ether molecules could push the spin-paired electrons of different calcium atoms to migrate towards the direction of Ca–Ca bonding.

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

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

<p>The aromaticity of cyclic 4<i>n</i>p-electron molecules in their first pp* triplet state (T<sub>1</sub>), labelled Baird-aromaticity, has gained growing attention in the last decade. Here we explore computationally the limitations of T<sub>1</sub> state Baird-aromaticity in macrocyclic compounds, <b>[<i>n</i>]CM</b>’s, which are cyclic oligomers of four different monocycles (M = <i>para</i>-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 T<sub>1</sub> 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 (<b>[<i>n</i>]CFU</b>’s) retain Baird-aromaticity until larger <i>n</i> than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a <b><sup>3</sup>[<i>n</i>]CFU</b> with a specific <i>n</i> is more strongly Baird-aromatic than the analogous <b><sup>3</sup>[<i>n</i>]CPP</b> while the magnetic indices tell the opposite. To construct large T<sub>1</sub> state Baird-aromatic <b>[<i>n</i>]CM</b>’s the design should be such that the T<sub>1</sub> 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 S<sub>0</sub> than benzene (<i>e.g.</i>, furan) that do not impose steric congestion are preferred. Structural confinement imposed by, <i>e.g.</i>, methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T<sub>1</sub> 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 T<sub>1</sub> states of the neutral macrocycles. </p>

scholarly journals Anti-ohmic Nanoconductors: Myth, Reality and Promise

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.

scholarly journals A BODIPY-Bridged Bisphenoxyl Diradicaloid: Solvent-Dependent Diradical Character and Physical Properties

Molecules ◽  
2019 ◽  
Vol 24 (8) ◽  
pp. 1446 ◽  
Author(s):  
Fang Miao ◽  
Hoa Phan ◽  
Jishan Wu
Keyword(s):  
Polar Solvent ◽  
Closed Shell ◽  
Dipole Interaction ◽  
Open Shell ◽  
Crystallographic Analysis ◽  
Structural Flexibility ◽  
Polar Solvents ◽  
X Ray ◽  
Diradical Character ◽  
Paramagnetic Activity

We report a new boron dipyrromethene (BODIPY)-bridged bisphenoxyl diradicaloid (2), which showed closed-shell diamagnetic character in less polar solvents such as dichloromethane but open-shell diradical character with paramagnetic activity in the very polar solvent N,N-dimethylformamide. X-ray crystallographic analysis of 2 revealed an anti-parallel stacked dimer structure via intermolecular dipole–dipole interaction, and the observed solvent-dependent diradical character can be explained by the different dihedral angles between the phenoxyl units and the BODIPY bridge, and structural flexibility of the molecule in different solvents. Compound 2 also exhibited solvent-dependent optical and electrochemical properties.

scholarly journals Nature of Bonding in Group 13 Dimetallenes: a Delicate Balance between Singlet Diradical Character and Closed Shell Interactions

2010 ◽  
Vol 49 (23) ◽  
pp. 10992-11000 ◽  
Author(s):  
Jani Moilanen ◽  
Philip P. Power ◽  
Heikki M. Tuononen
Keyword(s):  
Closed Shell ◽  
Group 13 ◽  
Delicate Balance ◽  
Diradical Character

Hydrostibination of Alkynes: A Radical Mechanism

2020 ◽  
Author(s):  
Josh MacMillan ◽  
Katherine Marczenko ◽  
Erin Johnson ◽  
Saurabh Chitnis
Keyword(s):  
Density Functional ◽  
Activation Barrier ◽  
Closed Shell ◽  
Reaction Rates ◽  
Radical Mechanism ◽  
Neutral Radical ◽  
Kinetic Isotope ◽  
Rate Limiting Step ◽  
Ionic Mechanisms ◽  
Terminal Acetylenes

The addition of Sb-H bonds to alkynes was reported recently as a new hydroelementation reaction that exclusively yields anti-Markovnikov <i>Z</i>-olefins from terminal acetylenes. We examine four possible mechanisms that are consistent with the observed stereochemical and regiochemical outcomes. A comprehensive analysis of solvent, substituent, isotope, additive, and temperature effects on hydrostibination reaction rates definitively refutes three ionic mechanisms involving closed-shell charged intermediates. Instead the data support a fourth pathway featuring neutral radical Sb<sup>II</sup> and Sb<sup>III</sup> intermediates. Density Functional Theory (DFT) calculations are consistent this model, predicting an activation barrier that is within 1 kcal mol<sup>-1</sup> of the experimental value (Eyring analysis) and a rate limiting step that is congruent with experimental kinetic isotope effect. We therefore conclude that hydrostibination of arylacetylenes is initiated by the generation of stibinyl radicals, which then participate in a cycle featuring Sb<sup>II</sup> and Sb<sup>III</sup> intermediates to yield the observed <i>Z</i>-olefins as products. This mechanistic understanding will enable rational evolution of hydrostibination as a methodology for accessing challenging products such as <i>E</i>-olefins.

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