The ionization energies of some phenothiazine tranquillizers and molecules of similar structure

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Abstract
Charge-transfer spectroscopy was used to determine the ionization energies of ten phenothiazine tranquillizers and similar molecules which are stimulants, in order to throw light on the proposed relation between physiological action and electron-donating power, and to compare the ionization energies of the phenothiazines with molecular orbital calculations. All the ionization energies obtained lie in the range 7.0-8.4 eV. The phenothiazines are thus strong electron donors, in agreement with calculations. There is little difference in ionization energies and equilibrium constants of complex formation between tranquillizers and either non-tranquillizers or stimulants. The difference in physiological action of the drugs therefore cannot be dependent on electron-donating power alone.