Phenazine Leuco Dyes and Applications

Phenazine leuco dyes, like their thiazine and oxazine analogues, have also found application in electrolytic recording, overhead transparencies, and Color Dry Silver. The phenazine leuco 48 is employed in electrolytic recording,17 whereas compounds 49, 50 are described as useful in thermographic and photothermographic systems.18 

Phenazine leucos are generally more reactive and more susceptible to air oxidation than the thiazines and oxazines. Incorporation of electron-withdrawing groups on the acyl substituent at the 10-position of the leuco dye can provide a substantial improvement in the thermal and light stability of the leuco form and it is found that in general the stronger the electron-withdrawing character of the acyl substituents the more stable the leuco is.18 

Phenazine leucos are capable of providing yellow, orange, red, and magenta images whereas thiazine and oxazine leucos are normally restricted to turquoise, blue, and purple colors.19 Color depends on the electronic nature of substituents R1 to R4, as shown in Table 3. 

Phenazine leucos until now are usually substituted at their 3 and 6 positions by amino groups due to the normal method of synthesis of the parent phenazine dyes. These types of leuco dyes are reactive. An alternative method of dye synthesis allows access to phenazine dyes with just one substituent at the 3-position.20 The resulting leuco dyes are called half diazine leucos. The loss of one exocyclic amino group leads to higher redox potential and results in less reactive leuco dyes, more useful in applications such as thermographic and photothermographic imaging, particularly Color Dry Silver. 

The new phenazine dyes are prepared according to established procedures with some modifications  

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