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configuration would lead to a correspondingly larger decrease in the stability of the naphthylazo compounds. The two dyes which contain an amino group in ortho position to the azo group again show a double band spectrum, probably as a result of the two possible paths of resonance, as described above. These compounds also show some phototropism (although their rate of reversal is also high), indicating that the hydrogen bond which is possible between the amino group and the azo nitrogen in these compounds is not as strong as that in dyes of Type III and V. The normal bathochromic effect of a methyl group is not discernible from the spectra of these two compounds.The spectra of the four azo dyes derived from d-naphthol (Type V) are not affected by irradiation of this type, probably because of the exist-ence of a strong hydrogen bond in these molecules, similar to that shown in Fig. 8. The strong displacement of the main absorption band toward longer wave lengths and the absence of a second band in the spectra of these compounds is consistent with this structure, since the formation of an additional chelate ring would be expected to cause a large bathochromic shift24 and to provide a single preferred path for the resonance in the molecule.

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