SQUARAINE CHEMISTRY - DESIGN, SYNTHESIS, AND XEROGRAPHIC PROPERTIES OF A HIGHLY SENSITIVE UNSYMMETRICAL FLUORINATED SQUARAINE

A novel unsymmetrical fluorinated squaraine (UFSq), 3,4-dimethoxyphenyl-2'-fluoro-4'-(dimethylamino)phenylsquaraine, which was designed to improve the spectral sensitivity of squaraine in the visible region has been synthesized. The effects of synthesis and purification on the xerographic properties have been examined. Direct or indirect condensation of 1-(3',4'-dimethoxyphenyl)-2-hydroxycyclobutene-3,4-dione with 3-fluoro-NN-dimethylaniline affords UFSq in very similar chemical yields. The physical, morphological, and xerographic properties of UFSq samples from both routes are very similar also. Purification of UFSq by solvent extraction improves the purity of the as-synthesized UFSq samples. It was concluded, based on melting points and xerographic data, that CH2Cl2 extraction produces the 'cleanest" sample for xerographic photoreceptor application. A bilayer device containing UFSq (CH2Cl2 Purified) was shown to exhibit a low dark decay value (-15 V/s) and high panchromatic photosensitivity from the visible to the near-IR regions. The energies required to photodischarge half of the initial surface potential are 3.1 and 1.9 ergs/cm2 at 600 and 790 nm, respectively. This sensitivity performance surpasses the sensitivity of all known squaraines and makes UFSq one of the most sensitive IR photoconducors known to date. Evidence is provided that the high sensitivity may be the result of the high purity and the high efficiency of hole injection of UFSq, from the charge generation layer to the charge-transporting layer, in the xerographic device. The electrical stability of UFSq is excellent. We have been able to show that the charging/photodischarging properties of an UFSq device remain unchanged after 50 000 cycles. This xerographic performance suggests that UFSq should be usable for diode laser (780 nm) and LED (660-680 nm) printers as well as copiers and multifunction printer-copiers.