Printing medium and use thereof

摘要

A printing medium which includes a substrate coated with a compound of the formula: <IMAGE> wherein R3 is a ring group having certain substituents in at least one ortho position with respect to the atom connected to C=O; and each R1 and R2 individually is aryl or alkaryl or are interconnected to form with the nitrogen atom a phenothiazine, phenoxazine, or phenazine or substituted derivative; and coated with an oxidizing agent or reduced form thereof; and method of use.