SQUARAINE CHEMISTRY - EFFECT OF N-PYRROLIDINO SUBSTITUTION ON THE SYNTHESIS AND SOLID-STATE PROPERTIES OF SQUARAINES

Several symmetrical and unsymmetrical squaraines bearing N-pyrrolidino groups have been synthesized by condensation of N-pyrrolidinoaniline derivatives with squaric acid or a 1-aryl-2-hydroxycyclobutene-3,4-dio ne derivative. As compared to squaraines synthesized from N,N-dimethyl anilines, a consistently higher synthetic yield was obtained for the N -pyrrolidino-squaraines synthesized in the work. The yield improvement is attributable to the high nucleophilicity of N-pyrrolidinoanilines, owing to the rigidized N-pyrrolidino ring structure. N-Pyrrolidino su bstitution is shown to have very little effect on the physical and spe ctroscopic properties of squaraine. Examinations of the solid state pr operties of N-pyrrolidino substituted squaraines, by solid state absor ption spectroscopy and by X-ray powder diffraction reveal that the N-p yrrolidino group is the only N-alkyl substituent identified thus far t hat exerts no effect on the aggregation of squaraine molecules in the microcrystalline state. This implies that N-pyrrolidino squaraines sho uld be photoconductive and indeed photoconductivities have been observ ed in xerographic devices incorporating them.