Conformation, distance, and connectivity effects on intramolecular electron transfer between phenylene-bridged aromatic redox centers

Journal of Physical Chemistry A

Volumn 106, Issue 10, 2002, Pages 2283-2292

  Rosokha, S V ^a   Sun, D L ^a   Kochi, J K ^a  

^a University of Houston   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

INTRAMOLECULAR ELECTRON EXCHANGES;

AROMATIC HYDROCARBONS; CONFORMATIONS; CYCLIC VOLTAMMETRY; ENERGY GAP; PARAMAGNETIC RESONANCE; POSITIVE IONS; REACTION KINETICS; REDOX REACTIONS; SURFACE TREATMENT;

CHARGE TRANSFER;

EID: 0037076112     PISSN: 10895639     EISSN: None     Source Type: Journal    
DOI: 10.1021/jp012634d     Document Type: Article

References (57)

1. Lindeman, S.V.; Rosokha, S.V.; Sun D.-L.; Kochi, J.K. J. Am. Chem. Soc. 2002, 124, 843.
2. (a) Mulliken, R.S.; Person, W.B. Molecular Complexes; Wiley: New York. 1969.
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4. (c) Hush, N.S. Electrochim. Acta. 1968, 13, 1005.
5. Creutz, C. Prog. Inorg. Chem. 1983, 30, 1.
6. For the few (earlier) studies of organic mixed-valence system that addressed the role of the bridge conformation, length and connectivity, see: (a) Nelsen, S.F.; Ismagilov, R.F.; Powell, D.R. 1997, 119, 10213.
7. (b) Nelsen, S.F.; Ismagilov, R.F.; Powell, D.R. J. Am. Chem. Soc. 1998, 120, 1924.
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11. (b) For the classification of a mixed-valence systems as class II, see: Robin, M.B.; Day, P. Adv. Inorg. Chem. Radiochem. 1967, 10, 247.
12. Structural changes in groups A-C donors and their cation radicals were generally too small for effective quantification by X-ray crystallography.
13. ox is measured as the potential difference between the first and second CV waves in Table 1, columns 3 and 4. For a discussion, see ref 1.
14. Estimated owing to the partially resolved (first and second) CV waves.
15. ET from the temperature-dependent linebroadening, see ref 1.
16. Sun, D.-L.; Lindeman, S.V.; Rathore, R.; Kochi, J.K. J. Chem. Soc., Perkin Trans. 2 2001, 1585.
17. +. redox center lie in the 400-500 nm region with a weak band at 700 nm.
18. (a) For analogous NIR transitions in the intermolecular (π-dimeric) complexes of aromatic cation radicals and donors, see: Kochi, J.K.; Rathore, R.; Zhu, C.-J.; Lindeman, S.V. J. Org. Chem. 2000, 112, 3671 and Le Maqueres, P.; Lindeman, S.V.; Kochi, J.K. J. Chem. Soc., Perkin Trans. 2 2000, 1180.
19. (a) For analogous NIR transitions in the intermolecular (π-dimeric) complexes of aromatic cation radicals and donors, see: Kochi, J.K.; Rathore, R.; Zhu, C.-J.; Lindeman, S.V. J. Org. Chem. 2000, 112, 3671 and Le Maqueres, P.; Lindeman, S.V.; Kochi, J.K. J. Chem. Soc., Perkin Trans. 2 2000, 1180.
20. (b) Analogous (pairwise) transitions have been observed in other organic mixed-valence systems. See Nelsen et al. in ref 4b.
21. The 2e oxidations of the D-br-D donors afford persistent dications that contain a pair of terminal cation radical centers, and are thus otherwise described as dication diradicals.
22. For the other analogues with n = 3 and 4, the serious (band) overlaps precluded the resolution of meaningful intervalence absorptions.
23. Compare also Nelsen et al. in ref 4b.
24. For example, the first and second ionization potentials of toluene are 8.83 and 9.36 eV, for p-xylene they are 8.67 and 9.15 eV, for biphenyl they are 8.34 and 9.04 eV, and for stilbene (vide infra) they are 7.87 and 9.08 eV.
25. See: Traven, V.F. Frontier Orbitals and Properties of Organic Molecules; Ellis Horwood: N.Y. 1992.
26. Howell, J.O.; Goncalves, J.M.; Amatore, C.; Klasinc, L.; Wightman, R.M.; Kochi, J.K. J. Am. Chem. Soc. 1984, 106, 3968.
27. +. (n = 3 and 4) are roughly the same.
28. The ionization potential of the bridge in FL is expected to be lower than that of fluorene (7.80 eV) by the extent of dialkyl substituents.
29. See: http://www.webbook.nist.gow.
30. Bandwidths (fwhm) were obtained by the deconvolution procedure and are presented in Table 5, column 4.
31. X-ray structural analysis of the FL cation radical shows unequal geometry of the terminal D groups that lead to quinonoidal distortions corresponding to +0.20 and +0.35 fractional positive charges, the remainder (4-0.45) being associated with the fluorenyl bridge.
32. A relatively large electronic interaction between the redox center D and the fluorenyl bridge (flu) must also be considered.
33. +., its ESR spectra were broadened at all temperatures (20 to -100 °C) and the computer simulation required the inclusion of additional hyperfine splittings (as an indication of the localized charge on the bridge).
34. Evans, C.E.B.; Naclicki, M.L.; Rezvani, A.R.; White, C.A.; Kondratiev, V.V.; Crntchtey, R.J. J. Am. Chem. Soc. 1998, 120, 13096.
35. (a) Generally the energetics (being as they are) will cause one superexchange mechanism to be dominant in a given mixed-valence system.
36. (b) Furthermore, this situation applies especially to organic mixedvalence systems owing to the relative spacings of p (and s) orbitals.
37. bD is substantially larger.
38. CT of the bDCT band evaluated from Table 4 (column 5).
39. CNS to within a factor of 2 is not uncommon (see refs 5 and 26).
40. ox) in solution for similarly constituted donors.
41. See: Astruc, D. Electron Transfer andRadical Processes in Transition-Metal Chemistry; VCH: New York, 1995.
42. +. in the previous paper.
43. Based on Marcus theory, as discussed by Sutin: (a) Sutin, N. Prog. Inorg. Chem. 1983, 30, 441.
44. (b) Brunschwig, B.S.; Sutin, N. Coord. Chem. Rev. 1999, 187, 233.
45. -1 were difficult to simulate with precision.
46. In addition, the significant charge density on the flu and st bridges suggests that the use of the two-state model may require modification.
47. +.) for X-ray crystallography. However the perpendicular conformation (φ = 90°) extant in the neutral donor D(dur)D suggests that the dur/D planes are also (nearly) orthogonal in the cation radical.
48. See Howell, J.O. et al. in ref 18.
49. 2D, the bridge/donor dihedral angles of φ = 31 (and 36)° compare with the intercyclic angle of φ = 17°, and a shortened bond of 1.47 Å compared with 1.49 Å in the neutral donor.
50. 2C- tie.
51. CNS) to be unreliable.
52. +. (see Tables 2 and 8). Unfortunately, the experimental rate constants at higher temperature (20 °C) were not compared owing to low accuracy.
53. Rathore, R.; Kumar, A.S.; Lindeman, S.; Kochi, J.K. J. Org. Chem. 1998, 63, 5847.
54. Perrin, D.D.; Armagero, W.L.; Perrin, D.R. Purification of Laboratory Chemicals, 2nd ed; Pergamon: New York, 1980.
55. Rosokha, S.V.; Kochi, J.K. J. Am. Chem. Soc. 2001, 123, 8985.
56. Forbes, W.F.; Sullivan, P.D. J. Phys. Chem. 1968, 48, 1411.
57. Heinzer, J., Quantum Chemistry Program Exchange 209, as modified by Petillo, P.A. and Ismagilov, R.F., Chemistry Dept., Indiana Univ., Bloomington, IN. We thank Prof. S.F. Nelsen for a copy of this program.