Oligothiophenes cation stabilization

Finally, it would be pertinent here to demonstrate that the present methodology of cation stabilization can be successfully applied to the preparation of a series of radical-cation salts and dication salts of oligothiophenes (2T, 3T, 4T, and 6T), fully annelated with BCO units, 24, 25, 26, and 27 (Figure 18) (31,32). 

Smaller oligothiophenes with n < 4 show a large tendency to dimerize to molecules with chain length 2n upon oxidation. Only by inclusion into (acidic) zeolites [199,200] can the dimerization be blocked, whereas a-substitution with methyl-groups does not hinder the dimerization at room temperature but slows it down [201,202]. Trimethylsilyl- [203], methoxy- and Br-a-substitution [204] stabilizes monomeric cations for ter-and in the two latter cases even for bithiophene. 

Synthesis and properties of cationic -conjugated systems stabilized by bicyclo[2.2.2]octene units including annulated silatropilium ion, thiophene, 1,2-dithiine, 1,4-dithiine, and oligothiophenes 05SL187. 

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