Octaaniline

We found that when fully reduced leucoemeraldine film is exposed to air, the 2 eV peak appeared quickly, within the first several hours. The intensity continued to increase for the first two days, saturated during the fourth day, and remained almost constant during several more days of exposure. The relative intensity of the 2 eV to 4 eV absorption peaks of this auto-oxidized and air-stabilized polyaniline was much smaller than that of the polyemeraldine base. Comparing with the spectra of the various oxidation states of octaaniline, we conclude that the degree of oxidation for this sample is near to y=0.25 (corresponding protoemeraldine). 

The reversibility (-99.7%) of the octaaniline sensor is excellent as shown in Figure 21. The environmental stability of the sensor is most satisfying. As can be seen from Figure 22, sensitivity, on exposure to a toluene/air mixture as discussed above, is reduced fairly rapidly during the first day of exposure to laboratory air, but then essentially stabilizes after a few days. 

Figure 21. Typical 120 seconds resistance responses of an octaaniline sensor to normal laboratory air, laboratory air saturated with toluene vapor at room temperature ( 26 torr 35,000ppm) and normal laboratory air.

Figure 22. Change in sensitivity (AR%) of an octaaniline sensor to saturated toluene vapor (25°C, -26.8 torr, 35,000ppm) as a function of number of days exposure of the sensor to ambient laboratory air at room temperature. Reproduced from reference 10.

Figure 23. Effect of water vapor in air at 25°C (23.7 torr 31,300ppm) on an octaaniline sensor. Reproduce with permission from Synthetic Metals (in press). Copyright 1998 Elsevier Science Ltd.

MacDiarmid et al. [332,333] reported the synthesis of octaani-line, an oligomer of aniline, and its use in a device to detect organic vapors such as toluene. The reversibility of the octaaniline sensor toward toluene vapors was observed to be excellent (99.7%) with a satisfactory environmental stability after a few days. 

In order to test if indeed PANI was an octaaniline, as proposed by Willstater and others and resurrected by Wnek, and in order to be able to make an oligomer with a known, specific number of quinoneimines we prepared, employing our condensation reaction mentioned above, a phenyl-capped octamer. We show below that three well defined oxidation slates leuco (white), per (magenta-violet), and emerald (blue) could be prepared and characterized. 

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