Occupation numbers of natural orbitals as a criterion for biradical character. Different kinds of biradicals

Doehnert, Detlef; Koutecký, J.

doi:10.1021/ja00526a005

Cited by 294 publications

(186 citation statements)

References 15 publications

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“…b Early theoretical considerations on o-and p-xylylene indicated this 'diradicaloid' character to be in the order of 30%, [138] a value which seems to be an overestimate based on our own calculations, whereas m-xylylene represents a 'true' diradical with a triplet ground state. [139,140] least one further good argument in favor of dimerization of monomer 3 as the source of the observed radicals: in this case, the energy required for diradical formation is compensated (at least partially) by the generation of two aromatic systems.…”

Section: The Radical Chain-growth Hypothesismentioning

confidence: 72%

The Gilch Synthesis of Poly(p‐phenylene vinylenes): Mechanistic Knowledge in the Service of Advanced Materials

Schwalm

Wiesecke

Immel

et al. 2009

Macromol. Rapid Commun.

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A consistent picture is presented of the mechanistic details and intermediates of the Gilch polymerization leading to poly(p-phenylene vinylenes) (PPVs). In-situ generated p-quinodimethanes are shown to be the real monomers, and spontaneous formation of the initiating radicals is effected by dimerization of some of these monomers to dimer diradicals, the latter also being the reason why significant amounts of [2.2]paracyclophanes are formed as side-products. Chain propagation predominantly proceeds by radical chain growth, occasionally interrupted by polyrecombination events between the growing α,ω-macro-diradicals. Based on this knowledge, oxygen is identified as a very efficient molar-mass regulating agent, and the temporary gelation of the reaction mixtures is interpreted to be the consequence of a very high entanglement of the polymers immediately after their formation. Last but not least, it is rationalized why the usually considered constitutional defects in Gilch PPVs might not be the only and most relevant ones with respect to the efficiency and durability of the organic light emitting devices produced thereof, and why cis-configurated halide-bearing vinylene moieties should be perceived as being among the most critical candidates. These considerations result in the recommendation of straightforward measures that should lead to clearly improved PPVs.

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Section: The Radical Chain-growth Hypothesismentioning

confidence: 72%

The Gilch Synthesis of Poly(p‐phenylene vinylenes): Mechanistic Knowledge in the Service of Advanced Materials

Schwalm

Wiesecke

Immel

et al. 2009

Macromol. Rapid Commun.

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“…The natural orbital (NO) is a key concept for estimating the amount, and its occupation number (NOON) is a good index of singlet biradical character. 28 The NOON values can be calculated by CASSCF or broken symmetry (BS) 29 UDFT calculation methods and the NOON of the lowest unoccupied natural orbital (LUNO) corresponds to the amount of singlet biradical character (y). For instance, a CASSCF(2,2)/6-31G calculation shows that p-quinodimethane (1) possesses a NOON of 0.097 for LUNO, leading to a y of 9.7%.…”

Section: Theoretical Treatment Of Singlet Biradical Charactermentioning

confidence: 99%

Recent Progress in Quinoidal Singlet Biradical Molecules

2014

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“…Therefore, numerous experimental and theoretical works have been performed to assess the S-T energy gaps in diradicals. [5][6][7][8][9][10][11][12][13] However, for designing polymer or solid ferromagnets, we must answer another key question, i.e., whether strong ferromagnetic coupling in diradicals can be maintained in extended systems with more than two unpaired electrons; for example, is "J" constant within homologous di-, tri-, and polyradicals? 14,15 In the present work, we probe this problem by investigating the spin coupling in three typical π-conjugated diradicals TMM, BQDM, and CPTMM and their homologous triradicals 16 ( Figure 2).…”

Section: Introductionmentioning

confidence: 99%

Is Ferromagnetic Spin Coupling Constant within Homologous Di- and Triradicals?

Jiang

1996

J. Phys. Chem.

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By means of the powerful Lanczos algorithm, the nonempirical valence bond (VB) model has been applied to investigate the low-lying electronic states for three typical types of homologous π-conjugated di-and triradicals. For small radicals including trimethylenemethane, cyclopentadienyltrimethylenemethane, mbenzoquinodimethane, and trimethylenebenzene, our VB results are in remarkable agreement with those obtained from previous sophisticated ab initio molecular orbital calculations. By using the energy difference between the high-spin ground and first excited states for these molecules, the strength of ferromagnetic coupling in these diradicals and their homologous triradicals has been discussed in detail. Our results reveal that ferromagnetic coupling in diradicals TMM and BQDM will decrease to different extent in their homologous triradicals. However, ferromagnetic coupling strength between two "unpaired" electrons in DCPP is found to be 9 times larger than that in its component diradical CPTMM.

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Occupation numbers of natural orbitals as a criterion for biradical character. Different kinds of biradicals

Cited by 294 publications

References 15 publications

The Gilch Synthesis of Poly(p‐phenylene vinylenes): Mechanistic Knowledge in the Service of Advanced Materials

The Gilch Synthesis of Poly(p‐phenylene vinylenes): Mechanistic Knowledge in the Service of Advanced Materials

Recent Progress in Quinoidal Singlet Biradical Molecules

Is Ferromagnetic Spin Coupling Constant within Homologous Di- and Triradicals?

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