Electrochemistry of solutions as well as simultaneous cyclic voltammetry and piezoelectric microgravimetry of conducting films of 2-(n-alkyl)fulleropyrrolidines

Effects of alkyl chain length and protonation of the pyrrolidine nitrogen on the electrochemical behavior of 2-(n-alkyl)fulleropyrrolidines, C(60)pyr-C-m (m = 4, 6, 8, 10, and 12), in solutions as well as in thin solid films are reported. Formal redox potentials of the first and second one-electron reversible electroreductions of C(60)pyr-C-m in 0.1 mol dm(-3) tetra(n-buryl)ammonium hexafluorophosphate in benzonitrile are shifted negatively by ca. 130 mV and that of the third electroreduction by ca. 240 mV with respect to the potentials of the corresponding C-60 redox couples. Protonation of the pyrrolidine nitrogen results in a positive shift of the formal redox potential of C(60)pyr-C-m in solution by ca. 90 mV, indicating more pronounced electron deficiency of the C-60 cage. Simultaneous cyclic voltammetry and piezoelectric microgravimetry of the drop-coated thin solid films of C(60)pyr-C-m in acetonitrile solutions reveals that the film solubility is larger the longer the alkyl chain and the more reduced the C-60 cage. Also, film stability with respect to dissolution is strongly dependent on the nature of the cation of the supporting electrolyte and acidity of solution. That is, the adduct films are more stable in the TBA(+) than Li+ solutions, similar to that of pristine C-60 films. Moreover, electroreduction of the adduct films in acidified Li+ solutions results in electrochemically inactive films. (C) 2000 The Electrochemical Society.