In search of through-solvent electronic coupling in flexible biradicals

Journal of the American Chemical Society

Volumn 118, Issue 19, 1996, Pages 4707-4708

  Forbes, Malcolm D E ^a   Ball, Jonathan D ^a   Avdievich, Nikolai I ^a  

^a University of North Carolina at Chapel Hill   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

RADICAL;

ARTICLE; COMPLEX FORMATION; MOLECULAR DYNAMICS;

EID: 0029894940     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja960101q     Document Type: Article

References (30)

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12. An advance in this regard has recently been presented by Kumar and co-workers (Kumar. K.; Waldeck, D. H.; Zimmt, M. B. J. Am. Chem. Soc. 1996. 118, 243).
13. who reported a strong solvent dependence of electron transfer rates in two rigid D/A complexes of different geometries. Cave et al. presented a theoretical analysis of this data (Cave. R. J.; Newton. M. D ; Kumar, K.; Zimmt, M. B. J. Phys. Chem. 1995, 99, 17501). modeling it using generalized Mulliken-Hush theory The results showed that changes in V were most likely responsible for the observed effects.
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24. (a) Photinos, D. J.; Poliks, J. B.; Samulski, E. T.; Terzis, A. F.; Toriumi, H. Mol. Phys. 1991, 72, 333.
25. (b) Application of methodology developed in ref 19a specifically to the problem of biradical J couplings is to be published: Avdievich, N. I.; Photinos, D. J.; Forbes, M. D. E. Manuscript in preparation.
26. -1.
27. Contribution from through-bond coupling anses in (J) as the chains populate more extended conformations, i.e., as the temperature is lowered. The extreme limit of this is when all chains assume the geometry of the all-trans conformer. On the basis of our results from other similar structures. we expect this mechanism to begin to dominate at temperatures below 220 K, which is outside the range considered here.
28. -1 for λ.
29. If conformational exchange is not fast, then dynamic effects are observed. The simulation routine then fails, and (J) cannot be determined. In all cases reported here. (J) is obtained from simulations that were successful, so we assume that all (J) values reported here are in the fast-exchange limit.
30. A way to envision the emergence of an elliptical topology at lower temperatures is to consider the extreme condition of slowly approaching absolute zero. If the chains can overcome all rotational barriers, a completely extended (and highly ordered) all-trans chain would result. This topology is described by a rigid rod. The high-temperature limit is the "fuzzy sphere", which must acquire more trans bonds (and become more ordered) as the temperature is lowered. It is clear that a topology between that of a sphere and a rod is an ellipse. At our experimental temperatures, motion of the chain is still fast, so that the "fuzzy" terminology still applies.