An azo compound excellent in solubility in solvent and having a high absorbance coefficient is disclosed, as well as an ink containing the azo compound. Such an ink contains a solvent having a relative permittivity at 22° C. and at a measurement frequency of 1 kHz of 3 or less and having a solubility in water at 25° C. of 20 mg/L or less, and an azo compound.

An azo compound excellent in solubility in solvent and having a high absorbance coefficient is disclosed, as well as an ink containing the azo compound. Such an ink contains a solvent having a relative permittivity at 22° C. and at a measurement frequency of 1 kHz of 3 or less and having a solubility in water at 25° C. of 20 mg/L or less, and an azo compound.

In a thermal transfer recording sheet including a base material and a colorant layer, the colorant layer includes a yellow dye layer containing a yellow dye, a magenta dye layer containing a magenta dye, and a cyan dye layer containing a cyan dye, and the cyan dye includes a compound represented by Formula (1a) or Formula (1b): ##STR00001##
where R.sub.1 to R.sub.7 are substituents, X.sup. is an anion, and the compound of Formula (1b) has at least one anionic substituent.

In a thermal transfer recording sheet including a base material and a colorant layer, the colorant layer includes a yellow dye layer containing a yellow dye, a magenta dye layer containing a magenta dye, and a cyan dye layer containing a cyan dye, and the cyan dye includes a compound represented by Formula (1a) or Formula (1b): ##STR00001##
where R.sub.1 to R.sub.7 are substituents, X.sup. is an anion, and the compound of Formula (1b) has at least one anionic substituent.

In a thermal transfer recording sheet including a base material and a colorant layer, the colorant layer includes a yellow dye layer containing a yellow dye, a magenta dye layer containing a magenta dye, and a cyan dye layer containing a cyan dye, and the cyan dye includes a compound represented by Formula (Ia) or Formula (Ib):

##STR00001##

where R.sub.1 to R.sub.7 are substituents, X.sup. is an anion, and the compound of Formula (Ib) has at least one anionic substituent.

In a thermal transfer recording sheet including a base material and a colorant layer, the colorant layer includes a yellow dye layer containing a yellow dye, a magenta dye layer containing a magenta dye, and a cyan dye layer containing a cyan dye, and the cyan dye includes a compound represented by Formula (Ia) or Formula (Ib):

##STR00001##

where R.sub.1 to R.sub.7 are substituents, X.sup. is an anion, and the compound of Formula (Ib) has at least one anionic substituent.

The invention discloses new substituted anthraquinone dyes that may be useful as cellular stains. In some aspect of the invention, the nuclear stains are useful for staining the nuclei of dead or fixed cells. Another aspect of the invention relates to substituted anthraquinone dyes comprising an enzyme substrate moiety that is transformable or cleavable by an enzyme such that the transformation or cleavage of the substrate moiety causes a detectable change in the functionality or spectral properties of the dye.