Azo Pigments and Their Intermediates. Synthesis, Characterization, and Xerographic Properties of Unsymmetrical Bisazo Pigments from 2-Nitro-4,4′-Diaminodiphenylamine

摘要

A series of unsymmetrical bisazo pigments, 1-15, have been synthesized by coupling the tetrazonium salt of 2-nitro-4,4′-diaminodiphenylamine with 2-hydroxy-3-naphthanilide couplers. Two types of solid-state behaviors are identified. The majority of the bisazo pigments studied undergo a bathochromic shift in the solid-state absorption spectrum when the pigment is processed from the powder form to the dispersed form in the charge generation layer (CGL) in xerographic devices. Three of the pigments are found to behave to the contrary; spectral blue shifts are obtained when they are incorporated in the CGLs under identical processing conditions. Devices with the red-shifted CGLs are found to exhibit relatively high charge acceptance, low dark decay, and low residual potential. The spectral response coincides with the red-shifted absorption, showing panchromatic responses from 400 to 700 nm. We attribute the result to a solid-state effect associated with the red shift. This xerographic result and the promising electrical cycling data suggest that the unsymmetrical bisazo pigments studied in this work would be useful as photogenerators in copiers as well as LED (680-nm) printers. Three analogous symmetrical bisazo pigments from bis(4-aminophenyl)amine (16-18) were synthesized. Their solid-state absorptions and xerographic properties were examined and compared with those of pigments 1-15. Results indicate that these three symmetrical bisazo pigments consistently undergo a spectral blue shift when the pigment is processed from the powder state to the dispersed state in the CGL. They also exhibit relatively low charge acceptance in xerographic devices. Hence we suggest that, because of the unsymmetrical structure in pigments 1—15, an intermolecular charge-transfer interaction occurs in the pigment particles in the CGL. This intermolecular charge-transfer interaction results in a spectral red shift and an enhanced photosensitivity in xerographic devices. The prospect of designing and synthesizing near-IR-sensitive unsymmetrical bisazo pigments for diode laser printers, which operate at 780 nm, is discussed.