Condições Otimizadas para Eletropolimerização de Alquilester-Tiofenos

Alkylthiophene derivatives are among the most widely studied monomers in the attempt to find ways to improve the processability of polythiophenes by increasing their solubilities in organic solvents. Generally, short alkyl-chains substituted thiophene derivatives are very difficult to polymerize by electrochemical methods, which requires a medium that favors the adsorption of the electrogenerated polymer. Frequently, it is observed in the literature erratic behaviors when conventional conditions are employed to electropolymerize ester-containing alkyl groups located on the 3-position of a thiophene monomeric unit [1,2]. Our main goal was to establish optimal electropolymerization conditions for six thiophene monomers 1-6 (Scheme 1) that display ester side groups with different sizes and topologies, and also to provide structure-polymerizability relationships. Basically, three different experimental conditions were employed: (a) a conventional condition (monomer 0.1 mol L-1 in TBABF4 0.1 mol L-1/CH3CN), (b) addition of a catalyst (mixture of TBABF4 0.1 mol L- 1/ACN:BF3 (1:1)) and (c) a high monomeric concentration (monomer 0.5 mol L-1 in TBABF4 0.1 mol L-1/CH3CN). While irregular deposits or no any-deposits for all monomers were frequently observed using (a), homogeneous films were obtained using (b) and (c) with reproducible results even up to 3 h of using the same aged monomeric solution. Older monomeric solutions showed the same undesirable behaviors observed in (a). The use of a longer spacer to separate the acetate/malonate moiety from the thienyl unit was found to efficiently favor/restore the reactivity of the thiophene monomer. That is, the monomers 3 and 4 were more reactive in comparison to 1 and 2, while 6 was polymerizable and 5 was not. Thus, it can be concluded that both (b) and (c) methodologies allow to efficiently electropolymerize thiophenes containing short ester side groups.