Synfacts 2007(1): 0041-0041  
DOI: 10.1055/s-2006-955676
Synthesis of Materials and Unnatural Products
© Georg Thieme Verlag Stuttgart · New York

Bent Radical Cation Dimers from Bicyclooctene-Substituted Terthiophenes

Contributor(s): Timothy M. Swager, Mark S. Taylor
D. Yamazaki, T. Nishinaga, N. Tanino, K. Komatsu*
Kyoto University and Tokyo Metropolitan University, Japan
Further Information

Publication History

Publication Date:
15 December 2006 (online)

Significance

The synthesis of bicyclooctene-substituted terthiophene 1, and the oxidation of this species to the corresponding radical cation are reported. Although the radical cation 1 did not dimerize in dilute (2.4 x 10-4 M) dichloro­methane solution at temperatures as low as 180 K, more concentrated (1.2 x 10-3 M) solutions displayed temperature-dependent changes in the UV-Vis and ESR spectra characteristic of π-dimer formation. In contrast, the fully substituted terthiophene 2 showed no propensity for dimerization in solution or in the solid state, due to the presence of bulky substituents on the central thiophene ring. In the solid-state structure of dimer (1 )2 (depicted schematically above), the terthiophene units are bent substantially from planarity, in order to relieve steric interactions between substituents. Heating (1 )2 in the solid state resulted in a new ESR signal assigned to a thermally excited triplet state, the first example of such an observation.