J . Am. Chem. SOL.1988, 110, 4468-4470
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Acknowledgment. We thank the Office of Naval Research, the Defense Advanced Research Projects Agency, and the National Science Foundation through the M.I.T. Materials Research Laboratory for partial support of this research. W e thank Professor R. J. Silbey for several valuable discussions. (13) Feldman, B. J.; Burgmayer, P.; Murray, R. W . J . Am. Chem. Sor.
I I I I I I I 8 1 I I f 1 I ' I ' I g I ' I ' I ' I poly (3-methylthiophene) transistor o t 500mVIsec S ~ / O . I M _ C ( ~ - B U ) ~ N ] P FVd ~ =25mV I
2
maximum conductivity is somewhat less. The observation of lowered conductivity in highly oxidized polythiophenes is consistent with theoretical expectations's8 and is similar to observations made for polyaniline.5,6 Considering the data for polyaniline,5s6I, and 11, it does appear that the polymer with the greatest conductivity, I, also has the widest region of conductivity. Earlier, studies of the potential dependence of the conductivity of polypyrrole have been reported for a limited potential range.9,13 We are currently investigating polypyrrole and its derivatives over a wider potential range to determine the width of the region of conductivity in these cases. Our findings have important practical implications relating to the use of conducting polymers I and I1 as electronic materials in batteries and microelectronic devices, since the polymers are shown to have a finite potential window where high conductivity occurs.
2.0
Figure 1. Top: Scan rate dependence for cyclic voltammetry of I on three adjacent Pt microelectrodes in S02/0.1M [(n-Bu),N]PF,. Bottom: Io-Vo characteristic for an adjacent pair of the microelectrodes coated with I for which cyclic voltammetry is shown. In the region of maximum ID, the current is partially limited by the significant resistance of the microelectrode leads (-200 0).All data are for solutions at -40 O C .
Figure 1 also shows the ID-VG characteristic in liquid S02/0.1 M [(n-Bu),N]PF, a t -40 "c for an adjacent pair of Pt microelectrodes connected with I. Negative of 0.6 V versus Ag, the ID-VG characteristic corresponds to that previously observed in both liquid and solid electrolyte systems.3*" The new finding is that the conductivity of I significantly declines as the polymer is further oxidized, as reflected in the small values of IDa t very positive values of V,. The polymer resistances at -0.2, +0.9, and +2.0 V versus Ag are >lolo R,
