Oligoacenes:  Theoretical Prediction of Open-Shell Singlet Diradical Ground States

Bendikov, Michael; Duong, Hieu M.; Starkey, Kyle; Houk, K. N.; Carter, Emily A.; Wudl, Fred

doi:10.1021/ja048919w

Cited by 704 publications

(700 citation statements)

References 15 publications

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“…It was recently shown that the lowest energy state of higher polyacenes can correspond to diradical singlet state instead of the closed-shell singlet state [59][60][61]. Similar results are also observed for some studied quinones.…”

Section: Resultssupporting

confidence: 77%

Why 1,2-quinone derivatives are more stable than their 2,3-analogues?

et al. 2015

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In this work, we have studied the relative stability of 1,2- and 2,3-quinones. While 1,2-quinones have a closed-shell singlet ground state, the ground state for the studied 2,3-isomers is open-shell singlet, except for 2,3-naphthaquinone that has a closed-shell singlet ground state. In all cases, 1,2-quinones are more stable than their 2,3-counterparts. We analyzed the reasons for the higher stability of the 1,2-isomers through energy decomposition analysis in the framework of Kohn–Sham molecular orbital theory. The results showed that we have to trace the origin of 1,2-quinones’ enhanced stability to the more efficient bonding in the π-electron system due to more favorable overlap between the SOMOπ of the ·C4n−2H2n–CH·· and ··CH–CO–CO· fragments in the 1,2-arrangement. Furthermore, whereas 1,2-quinones present a constant trend with their elongation for all analyzed properties (geometric, energetic, and electronic), 2,3-quinone derivatives present a substantial breaking in monotonicityThis work has been supported by the European Union in the framework of European Social Fund through the Warsaw University of Technology Development Programme. O.A. S., H. S. and T.M. K. gratefully acknowledge the Foundation for Polish Science for supporting this work under MPD/2010/4 project "Towards Advanced Functional Materials and Novel Devices-Joint UW and WUT International PhD Programme" and the Interdisciplinary Center for Mathematical and Computational Modeling (Warsaw, Poland) for providing computer time and facilities. Thanks are also to the Ministerio de Economia y Competitividad of Spain (Projects CTQ2011-23156/BQU and CTQ2011-25086) and the Generalitat de Catalunya (project numbers 2014SGR931, Xarxa de Referencia en Quimica Teorica i Computacional, and ICREA Academia 2014 prize for MS

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Section: Resultssupporting

confidence: 77%

Why 1,2-quinone derivatives are more stable than their 2,3-analogues?

et al. 2015

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“…Houk has observed a similar effect for polyacenes, some of which are computed by DFT to have open-shell singlet ground states as a result of the disjoint nature of the triplet SOMOs (that study also employed the broken-symmetry method for the singlet states). 47 The disjoint nature of the triplet SOMOs for this ion 13 contrasts with the xanthenyl ions (1−8) and coumarinyl ions (17−19), which share SOMO wave function amplitude on some of the same atoms (Figure 2). Thus, for these latter species the triplet configuration would be expected to have a non-negligible exchange energy and is computed to be lower in energy than the open-shell singlet configuration.…”

Section: Journal Of the American Chemical Societymentioning

confidence: 93%

A Fine Line Separates Carbocations from Diradical Ions in Donor-Unconjugated Cations

Albright

Winter

2015

J. Am. Chem. Soc.

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Carbocations are traditionally thought to be closed-shell electrophiles featuring an empty orbital rich in p character. Here, density functional theory computations indicate that when strong π donors are not placed in direct conjugation with benzylic-type cations, alternative diradical configurations that resemble non-Kekulé diradicals are possible. For certain donor-acceptor frameworks, an open-shell singlet configuration is the computed ground state for the cation, whereas for coumarin and xanthenyl cations substituted with strong donors, a triplet diradical configuration is the computed ground state. Changing the substituent nature and attachment location substantially alters the energy gaps between the different electronic configurations and can manipulate the computed ground-state electronic configuration. There are few known examples of ground-state triplet carbocations, and, to our knowledge, no other examples of open-shell singlet carbocations. The open-shell singlet and triplet "carbocations" described here may have reactivity distinct from that of typical closed-shell singlet carbocations and, if appropriately stabilized, lead to organic materials with interesting electronic and magnetic properties. ABSTRACT: Carbocations are traditionally thought to be closedshell electrophiles featuring an empty orbital rich in p character. Here, density functional theory computations indicate that when strong π donors are not placed in direct conjugation with benzylictype cations, alternative diradical configurations that resemble nonKekulédiradicals are possible. For certain donor−acceptor frameworks, an open-shell singlet configuration is the computed ground state for the cation, whereas for coumarin and xanthenyl cations substituted with strong donors, a triplet diradical configuration is the computed ground state. Changing the substituent nature and attachment location substantially alters the energy gaps between the different electronic configurations and can manipulate the computed ground-state electronic configuration. There are few known examples of ground-state triplet carbocations, and, to our knowledge, no other examples of open-shell singlet carbocations. The open-shell singlet and triplet "carbocations" described here may have reactivity distinct from that of typical closed-shell singlet carbocations and, if appropriately stabilized, lead to organic materials with interesting electronic and magnetic properties.

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“…Indeed, this hexagonal nano-flake has attracted great interest with respect to its interesting properties like electronic absorption spectra, 119 and it has been successfully applied for modeling graphene in previous theoretical work. [120][121][122][123][124] Several theoretical studies have focussed on acenes [125][126][127] and oligoacenes [128][129][130][131][132] using DFT and ab-initio methods. However, because of the polyradical character of oligoacenes, 125,126 the spin ground state of these molecules have to be checked.…”

Section: Graphene Modelmentioning

confidence: 99%

“…[120][121][122][123][124] Several theoretical studies have focussed on acenes [125][126][127] and oligoacenes [128][129][130][131][132] using DFT and ab-initio methods. However, because of the polyradical character of oligoacenes, 125,126 the spin ground state of these molecules have to be checked. Singlet-triplet (S-T) excitation energies give valu- 137 The first S-S and S-T excitation energies were calculated to 1.94 and 1.77 eV, respectively.…”

Section: Graphene Modelmentioning

confidence: 99%

Chemical Bonding and Electronic Properties of the Co Adatom and Dimer Interacting with Polyaromatic Hydrocarbons

2015

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The density functional calculations presented here elucidate the nature of the interaction between the Co atom and dimer with a polyaromatic hydrocarbon (PAH). The results are analyzed in terms of structural, electronic and magnetic properties. The bonding character of the Co atom and dimer adsorbed on the PAH exhibits a strong covalent bonding, arising from a hybridization between the d orbitals of Co and the p z orbitals of the carbon atoms, which cause an in-plane distortion in the PAHs. A small charge transfer takes place from the Co atom and dimer to the PAH surface, which creates a positive charge on the metal atoms and thereby change their catalytic activity. Upon adsorption, the magnetic moment of the Co adatom is reduced depending on the adsorption site. For the perpendicular Co dimer to the PAH plane, the projected magnetic moment of the Co atom further from the PAH is increased, which is due to antiferromagnetic coupling between the Co atoms in this configuration. Density of state analysis shows that the main contribution of magnetic moment reduction is due to promotion of electrons from the 4s states to the 3d states of the Co adatom upon adsorption.

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Oligoacenes: Theoretical Prediction of Open-Shell Singlet Diradical Ground States

Cited by 704 publications

References 15 publications

Why 1,2-quinone derivatives are more stable than their 2,3-analogues?

Why 1,2-quinone derivatives are more stable than their 2,3-analogues?

A Fine Line Separates Carbocations from Diradical Ions in Donor-Unconjugated Cations

Chemical Bonding and Electronic Properties of the Co Adatom and Dimer Interacting with Polyaromatic Hydrocarbons

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