Letter | Published:

Electronic Properties of Imidazole

Naturevolume 191pages379380 (1961) | Download Citation



THE existence of semiconduction has been demonstrated in a variety of different classes of organic compounds such as condensed aromatic hydrocarbons, charge-transfer complexes, pyrolized polymers, and stable free radicals. With few exceptions, the electrical conductivities are small, and the energies of activation for the conduction process are high. But the fact that even small conductivities are displayed suggests that some kind of intermolecular interaction takes place which, in an electric field, gives rise to electronic conduction. It is suggested that this interaction is molecular orbital overlap. The extent of orbital overlap is a function of molecular structure and hence, if semiconduction arises from such overlap, it is not surprising that semiconduction activation energies correlate with properties which are also a function of molecular structure, such as the molecular ionization energy, electron affinity, and excitation energy of the ground-triplet state transition1,2. One of the entities which influences these properties is the number of (the more easily polarizable) π-electrons. As the number of these increases in a conjugated system, there is a trend toward smaller activation energies of conduction, indicating that the probability of achieving overlap is enhanced by the presence of a large number of π-electrons. However, if the overlapping of molecular orbitals gives rise to semiconduction, then any other factors which contribute to such overlapping should also encourage semiconduction, even if only few π-electrons are present in the individual molecule. Since intermolecular hydrogen bonds may provide such overlap, it might be expected that activation energies in hydrogen-bonded compounds should be lower than anticipated solely on the basis of the number of π-electrons.

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  1. 1

    Lyons, L. E., and Morris, G. C., J. Chem. Soc., 3648 (1957).

  2. 2

    Aftergut, S., and Brown, G. P., Nature, 189, 827 (1961).

  3. 3

    Eley, D. D., Inokuchi, H., and Willis, M. R., Disc. Farad. Soc., No. 28, 54 (1959).

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  1. General Engineering Laboratory, General Electric Co., Schenectady, New York

    •  & G. P. BROWN


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