AZO PIGMENTS AND THEIR INTERMEDIATES - A SPECTROSCOPIC ASSESSMENT OF METAL AZO COMPLEXES AS NEGATIVE CHARGE CONTROL AGENTS IN COLOR TONERS

The potential of a class of black, but effective, negative charge cont rol additives-namely, 1:2 Cr/Azo complexes-for color toner application has been assessed spectroscopically. Absorption spectral data of Aize n Spilon Black TRH, its azo ligand, a model azo compound, and a model Cr(III) ion suggest that the visible absorption of TRH originates from the aw ligand. This conclusion is supported by low-temperature spectr al results. Two approaches to rendering Cr/Azo complexes visibly trans parent, such that they become useful in color toners, are put forward. One of the approaches is to extend the Cr/Azo complex absorption to t he near-IR (>700 nm). Initial data indicate that this approach may be hindered by the Franck-Condon effect on the electronic transition. On the other hand, yellow Cr/Azo complexes with lambda(max) at approximat ely 450 nm are known. Because the absorption of Cr/Azo complex is show n to originate from the azo ligand, and the bathochromic shift from li gand to complex is approximately 50 nm, a second approach is to synthe size near-UV-absorbing, visibly transparent Cr/Azo complexes that abso rb <400 nm. This approach requires the identification of azo ligands w ith absorption wavelengths <350 nm. Probable structures of azo ligands are proposed and discussed.