Certain classes of phenothiazine and phenoxazine dyes are known and have been used for a variety of purposes for many years. Examples of these phenothiazine dyes include Methylene Blue (C.I. 52015), Thiocarmine R (C.I. 52035), Lauth's Violet (C.I. 5200), and Azure B (C.I. 52010). These dyes range from turquoise (Methylene Blue Dmax=660 nm) to violet (Lauth's Violet Dmax=590 nm) in color. Similarly, phenoxazines include Capri Blue (C.I. 51000), Brilliant Cresyl Blue (C.I. 51010), and Nile Blue (C.I. 51180), which also range in color from turquoise to blue.
The leuco forms of these classes of phenoxazine and phenothiazine dyes are useful in imaging systems. Copikem II.TM. (Hilton-Davis) is a benzoyl leuco thiazine and Pergascript Turquoise S2G.TM. (Ciba-Geigy) is a benzoyl leuco oxazine. Both give rise to turquoise color on reversion to the dye form and as such are useful in carbonless systems (e.g., see U.S. Pat. No. 2,646,367), thermographic systems (e.g., see U.S. Pat. No. 3,447,944), and electrochromic systems (e.g., see U.S. Pat. No. 4,309,255). Their use is limited to applications where blue is the only color necessary. Two- or three-color imaging is not possible due to the limited range of colors known in the thiazine and oxazine dye classes.
Compounds of the formula ##STR3## wherein R' is methyl, ethyl, or iso-butyl, are disclosed by G. A. Khutormenko et al. in "Pharmacological Chemistry Journal", Vol. 10, at page 83 (1976), having utility as a pharmacologically active compound having antiarrhythmic properties. These compounds have not been used as dyes or color formers.
Japanese Kokai No. 73 52 778 (and abstract) discloses phenoxazine leuco dyes capable of providing dyes in shades of blue.