Electronic absorption spectra of basic dyes containing terminal diethylamino and morpholino groups

Sawyer, John (1978) Electronic absorption spectra of basic dyes containing terminal diethylamino and morpholino groups. Masters thesis, Preston Polytechnic.

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Comprehensive series of methyl and triuluoromethyl derivatives of Brilliant Green and Morpholine Green have been synthesised and their visible absorption spectra have been correlated with structural features.
The spectral data for the parent dyes have been compared with those for Malachite Green and the differences have been
interpreted in terms of the relative basicity of the terminal groups.
Where substitution occurs in the meta- and para-positions of the phenyl ring, it has been shown that the wavelength of
maximum absorption bears a linear relationship to the appropriate Hammett substitution constant. Observed,\ max values for
disubstituted compounds are in good agreement with the values calculated on the basis of additivity effects of substituents.
The spectral parameters for the ortho-substituted dyes are consistent with enforced rotation of the phenyl ring out of the
plane of the molecule. The effect is enhanced following substitution into the second ortho-position. The effect of substitution in one or both of the diethylaminophenyl rings of Brilliant Green has been investigated. The observed red shift of the x-band arising from substitution of a methyl group into the ortho-position suggests that steric effects are shared between both rings and that electronic symmetry is maintained. However, introduction of one otho-trifluoromethyl group leads to a blue shift which duggests that electronic symmetry is lost and that the substituted ring experiences all of the rotation. An ortho-trifluororiethyl group in the second diethylaninophenyl ring restores electronic symmetry.
The blue shift and marked reduction in intensity consequent upon substitution in the nieta-position of the diethylaminophenyl
rings is consistent with steric interaction between the substituent and the terniinal group resulting in a decrease in conjugation of the latter group with the TPM system.
The observed spectral changes for the Brilliant Green and Norpholine Green series are in general agreement with the recorded data for the analogous Malachite Green derivatives.

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