Influence of π-Stacking on the Redox Properties of Oligothiophenes: (r-Alkyloligo-thienyl)para[2.2]cyclophanes Fouad Salhi, Byunghun Lee, Christopher Metz, Lawrence A. Bottomley, and David M. Collard* School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400 daVid.collard@chemistry.gatech.edu Received May 20, 2002 ABSTRACT Oligothienyl-substituted paracyclophanes bearing r-thienyl substituents, which block polymerization at these sites, undergo oxidation to form stable radical cations and dications. Splitting of the first voltammetric oxidation wave of stacked dimers into two single-electron processes corresponding to formation of the stacked mono(radical cation) and the stacked bis(radical cation) illustrates the influence of π-stacking on the behavior of conjugated chains, which serve as models for stacked polarons in conjugated polymers. The conductivity of doped conjugated organic polymers requires migration of delocalized carriers (solitons, polarons, bipolarons) along conjugated chains and through π-stacks. 1 However, most physical-organic studies of this process make use of linear polyenes as one-dimensional models, which are used only to probe the delocalization and migration of carriers along individual noninteracting chains. 2 The effect of stacking model charge carriers has been addressed by the covalent linkage of conjugated oligomers 3 and by assembly of π-dimers of ion radicals in solution. 4 The through-space electronic interaction between neutral and charged stacked arenes has previously been studied by examination of substituent effects, 5 spectroscopy, 6,7 and electrochemistry 8,9 of cyclophanes in which the stacking interaction is fixed through covalent bonds. The effect of stacking on delocalized excitons of neutral chromophore- substituted cyclophanes has been addressed extensively by Bazan. 10 We have undertaken a study of cationic (i.e., p-doped) oligothiophene-substituted [2.2]paracyclophanes in an attempt to introduce a second dimension to models of delocalized charge carriers in conjugated, conducting, poly- mers. Previous reports show that bis(2-thienyl)-cyclophane, CP-Th 2 , 11 along with the bis(dithienyl) 12 analogue, is subject to electrooxidative polymerization through the un- (1) Cornil, J.; Beljonne, D.; Calbert, J.-P.; Bredas, J.-L. AdV. Mater. 2001, 13, 1053. (2) Tolbert, L. M. Acc. Chem. Res. 1992, 25, 561 (3) Kaikawa, T.; Takimiya, K.; Aso, Y.; Otsubo, T. Org. Lett. 2001, 2, 4197. (4) Miller, L. L.; Mann, K. R. Acc. Chem. Res. 1996, 29, 417. (5) Cram, D. J.; Bauer, R. H. J. Am. Chem. Soc, 1959, 81, 5971. (6) Boydston, A. J.; Bondarenko, L.; Dix, I.; Weakley, T. J. R.; Hopf, H.; Haley, M. M. Angew. Chem., Int. Ed. 2001, 40, 2986. (7) Longonne, D. T.; Glans, J. H. J. Polym. Sci. A: Polym. Chem. 1988, 26, 405. (8) Dietrich, M.; Mortensen, J.; Heinze, J. J. Chem. Soc., Chem. Commun. 1986, 1131. (9) Warini, A. R.; Valenzuela, J.; Staab, H. A.; Neugebauer, F. A. Eur. J. Org. Chem. 1998, 139. (10) Bartholomew, G. P.; Bazan, G. C. Acc. Chem. Res. 2001, 34, 30. Zyss, J.; Ledoux, I.; Volkov, S.; Chernyak, V.; Mukamel, S.; Bartholomew, G. P.; Bazan, G. C. J. Am. Chem. Soc. 2000, 122, 11956. Bartholomew, G. P.; Bazan, G. C. J. Am. Chem. Soc. 2002, 124, 5183. ORGANIC LETTERS 2002 Vol. 4, No. 19 3195-3198 10.1021/ol026211l CCC: $22.00 © 2002 American Chemical Society Published on Web 08/27/2002