Effect of Pressure on the Resistance of Fused-Ring Aromatic Compounds

The effect of pressure to several hundred kilobars has been measured on the resistance of seven-fused ring aromatic compounds, including two polyacenes and five quinones. In general, there is a rapid drop in resistance at lower pressures, followed by a marked leveling at above 200–250 kbars. The leveling is apparently associated with the rapid decrease in compressibility at high pressure observed by Bridgman. The resistance at high pressure varied by several orders of magnitude among the compounds. It seems to be closely associated with the amount of overlap between adjacent molecules in the unit cell. The temperature coefficient of resistance at high pressure was obtained for three compounds. They all remained semiconductors at the highest pressure studied, but the activation energy was about one-sixth of the atmospheric pressure value.