Lophine Dyes for Printing
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
As electrochemically active leucodyes for printing, the lophine (triarylimidazole) dyes are a promising class of materials. The representative lophine leucodye 1. is prepared in a straightforward fashion by condensation of 4-hydroxy-benzaldehyde and anisil with ammonium acetate in acetic acid. Leucodye 1 is readily oxidized by bromine to the stable red dye 2. (Image Omitted) A minimum of at least one of the aromatic rings in the aldehyde or benzil precursor must contain a "chromogenic" substituent such as an alcohol or amine in a position ortho or para to the attachment to the imidazole ring in order to allow oxidation to the dye form. A wide variety of aldehydes and benzils may be combined to give lophines with a range of oxidation potentials and resultant dyes with a wide variety of colors.