Oligoacenes: Theoretical prediction of open-shell singlet diradical ground states

Journal of the American Chemical Society

Volumn 126, Issue 24, 2004, Pages 7416-7417

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

^a UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

BENZENE; OLIGOACENE; POLYCYCLIC AROMATIC HYDROCARBON; RADICAL; UNCLASSIFIED DRUG;

ARTICLE; ELECTROCHEMISTRY; ENERGY; GEOMETRY; SEMICONDUCTOR; THEORY;

EID: 2942656823     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja048919w     Document Type: Article

References (29)

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15. 2 values different from 0 (pure singlet) or 1 (pure triplet).
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18. Re-optimization of the geometry at the UDFT level also led to a lowering of the energy, which can be considered as a second criterion describing the instability of the RDFT solution (Gräfenstein, J.; Hjerpe, A. M.; Kraka, E.; Cremer, D. J. Phys. Chem. A 2000, 104, 1748-1761).
19. Unrestricted DFT is adequate for studying concerted vs diradical pathways of the Diels-Alder reaction (Goldstein, E.; Beno, B.; Houk, K. N. J. Am. Chem. Soc. 1996, 118, 6036) and the Bergman cyclization (Gräfenstein, J.; Hjerpe, A. M.; Kraka, E.; Cremer, D. J. Phys. Chem. A 2000, 104, 1748-1761), which includes diradical intermediates. Here UDFT provided results similar to CASSCF or CASPT2 as well as for other radical reactions (Rienstra-Kiracofe, J. C.; Allen, W. D.; Schaefer, H. F., III. J. Phys. Chem. A 2000, 104, 9823-9840) where UDFT and CCSD(T) levels give similar results.
20. Unrestricted DFT is adequate for studying concerted vs diradical pathways of the Diels-Alder reaction (Goldstein, E.; Beno, B.; Houk, K. N. J. Am. Chem. Soc. 1996, 118, 6036) and the Bergman cyclization (Gräfenstein, J.; Hjerpe, A. M.; Kraka, E.; Cremer, D. J. Phys. Chem. A 2000, 104, 1748-1761), which includes diradical intermediates. Here UDFT provided results similar to CASSCF or CASPT2 as well as for other radical reactions (Rienstra-Kiracofe, J. C.; Allen, W. D.; Schaefer, H. F., III. J. Phys. Chem. A 2000, 104, 9823-9840) where UDFT and CCSD(T) levels give similar results.
21. Unrestricted DFT is adequate for studying concerted vs diradical pathways of the Diels-Alder reaction (Goldstein, E.; Beno, B.; Houk, K. N. J. Am. Chem. Soc. 1996, 118, 6036) and the Bergman cyclization (Gräfenstein, J.; Hjerpe, A. M.; Kraka, E.; Cremer, D. J. Phys. Chem. A 2000, 104, 1748-1761), which includes diradical intermediates. Here UDFT provided results similar to CASSCF or CASPT2 as well as for other radical reactions (Rienstra-Kiracofe, J. C.; Allen, W. D.; Schaefer, H. F., III. J. Phys. Chem. A 2000, 104, 9823-9840) where UDFT and CCSD(T) levels give similar results.
22. Open-shell ground-state singlet disjoint diradicals have been discussed in detail by Borden and Davidson and others. (a) Borden, W. T.; Davidson, E. R. J. Am. Chem. Soc. 1977, 99, 4587,
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29. According to the Su-Schrieffer-Heeger (SSH) model, the effective length of a soliton in a π-system is about 14 carbon atoms: Heeger, A. J.; Kivelson, S.; Schrieffer, J. R.; Su, W.-P. Rev. Mod. Phys. 1988, 60, 781-850. This is in agreement with our calculations, predicting diradical character in oligoacenes, and thus, hexacene-heptacene have already enough π-length (two 13-15 carbon atom chains, respectively) to produce two oligoacetylene solitons.