Effect of Pressure on the Properties of TCNQ and Its Complexes

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Abstract
The effect of very high pressure has been measured on the properties of TCNQ (tetracyanoquinodimethane) and three complexes. For all three complexes the electrical resistance at 296°K decreased with increasing pressure to about 140–150 kbar, beyond which pressure there was a very large rise accompanied by much drifting upward with time. This transformation was irreversible. At 78°K no rise was noted at high pressure, but if a sample was heated at high pressure the transformation initiated about 180°K. It was found that the absorption peaks in the visible region had almost completely disappeared in the transformed material although the 280‐mμ peak remained. The resistance of TCNQ was too high to permit electrical studies, but samples taken to high pressure also showed disappearance of absorption peaks in the visible. These and other related observations indicate that the TCNQ molecules are reacting, probably through the C≡N bond. The type of reaction seems in many ways similar to that obtained in pentacene and single‐crystal graphite and discussed in a previous paper.