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Violanthrone, iso-violanthrone, and pyranthrone have electrical conductance to a certain degree. This is due to the molecular structure of these compounds, which are made of the network planes of carbon atoms, and to the assumption that the π-electron contribute to the electrical conduction. The electrical resistivity of violanthrone, iso-violanthrone, and pyranthrone was measured. The values at 15°C are as follows; 2.3×1010 ohm-cm, 5.7×109 ohm-cm, and 3.9×1015 ohm-cm respectively. The resistivity decreases with increasing temperature in every case, and a good linear relationships is observed between the logarithm of the resistivity and the reciprocal of the temperature. As the activation energy of the electrical conductance, the following values were observed; 0.39 ev, 0.375 ev, and 0.53 ev respectively. The values for violanthrone and iso-violanthrone suggest that they can be assumed to be intrinsic semi-conductors.

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It was found that most polycyclic aromatic hydrocarbons form molecular complexes with bromine or iodine. Those complexes which are black behave as typical semiconductors with energy gaps for conductivity of 0.1–0.2 eV., as well as with low electrical resistivity ranging from 10° to 103 ohm-cm. The complexes are unstable and a substitution reaction of halogen takes place; when this is not the case, e. g. the violanthrene-iodine complex, and the complex itself is quite stable, so also is the electrical property. It is concluded that the origin of the high conductivity is due to the interaction between hydrocarbon molecules and halogen molecules, and this is presumably due to the overlapping of molecular orbitals stretching throughout the crystal.

The magnetic susceptibilities of condensed polynuclear aromatic compounds with higher molecular weights (ten hydrocarbons and twelve quinones) have been measured by the Gouy method, and the diamagnetic anisotropies have been approximately evaluated. The diamagnetic anisotropy becomes progressively large as the number of rings increases, when the aromatic condensation takes place in the manner of the closely compact arrangement of rings; while, when it is not the case, it depends strikingly upon the molecular structure. When the diamagnetic anisotropy has a smaller value, notwithstanding the molecule is made of a large number of rings, the localization of the π-electrons or some other excited states must be assumed. Such a case is found, when a molecule is not made of the aromatically conjugated system as a whole but separated into two predominant nuclei, as meso-naphthodianthrene and violanthrone, or when a molecule is made of a long shaped structure as pyranthrene or violanthrene.

Stable cation radical salts were prepared by oxidation of perylene, 9,10-diphenylanthracene, 9,10-dimethylanthracene, and 9,10-dichloranthracene with antimony pentachloride. Perylene perchlorate was also obtained in a stable form. From the temperature variations of their paramagnetic susceptibilities, the exchange coupling constants for these salts were found to increase in the sequence of above listing ranging from ∼0 to 8.5×10−2 eV. The absorption spectra of these solid compounds were compared with those observed with solutions. While the absorption bands of each salt in the visible region were found to correspond to those of the solution spectrum of the respective compound, an extra absorption band was observed in the near-infrared region for compounds with larger exchange coupling constants. The appearance of the new absorption band was reasonably ascribed to charge-transfer interaction between the radicals. These observations are considered to support further our previous suggestion that the magnitude of the exchange coupling constant obtained through magnetic measurements is basically determined by the stabilization energy due to the charger-transfer configurational interaction.

Photoconductivity of violanthrone, iso-violanthrone, and pyranthrone, the organic semiconductors, has been investigated. From the threshold of spectral response of photoelectric current, the energy gap between the full ground band and the empty excited band was estimated as 0.84 ev, 0.93 ev, and 1.14 ev, respectively. These results are in good agreement with that estimated from the temperature dependence of resistivity, and furthermore with the optical absorption of crystals.