AZO PIGMENTS AND THEIR INTERMEDIATES - SYNTHESIS, CHARACTERIZATION, AND XEROGRAPHIC PROPERTIES OF UNSYMMETRICAL BISAZO PIGMENTS FROM 2-NITRO-4,4'-DIAMINODIPHENYLAMINE

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 beh aviors are identified. The majority of the bisazo pigments studied und ergo 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 th e pigments are found to behave to the contrary; spectral blue shifts a re obtained when they are incorporated in the CGLs under identical pro cessing conditions. Devices with the redshifted CGLs are found to exhi bit relatively high charge acceptance, low dark decay, and low residua l potential. The spectral response coincides with the red-shifted abso rption, showing panchromatic responses from 400 to 700 nm. We attribut e the result to a solid-state effect associated with the red shift. Th is xerographic result and the promising electrical cycling data sugges t 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)a mine (16-18) were synthesized. Their solid-state absorptions and xerog raphic properties were examined and compared with those of pigments 1- 15. Results indicate that these three symmetrical bisazo pigments cons istently undergo a spectral blue shift when the pigment is processed f rom the powder state to the dispersed state in the CGL. They also exhi bit 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 p articles in the CGL. This intermolecular charge-transfer interaction r esults in a spectral red shift and an enhanced photosensitivity in xer ographic devices. The prospect of designing and synthesizing near-IR-s ensitive unsymmetrical bisazo pigments for diode laser printers, which operate at 780 nm, is discussed.