Methyl and ethyl ring-substituted polyaniline derivatives have been synthesized and characterized by UV-visible-near IR spectroscopy. Optical spectra of the base forms in DMF solution suggest that the torsion angle between adjacent rings is increased by steric hindrance due to the alkyl groups in the substituted polymers, leading to blue shifts in the ∼4 eV (“bandgap”) and ∼2 eV (“exciton”) absorptions and an accompanying decrease in the relative intensity of the “exciton” band.
The methyl ring-substituted derivative, poly(o-toluidine), is shown to exhibit solvatochromism. The “exciton” absorption shifts from 2.03 eV in pure NMP to 2.19 eV in CH2CI2, accompanied by a loss in intensity relative to the “exciton” absorption.The phenomenon is attributed to the presence of a more “rod-like” state in NMP as compared to a more “coil-like” state in CH2CI2.
The effects of alkyl substituents on acetic acid solution spectra of “emeraldine” salt will be discussed with respect to polaron band formation in these systems.