Disclosed is a mono-azo dichroic dye compound represented by the following Chemical Formula 1, a composition for polarizing plate, a polarizing plate, and an optical device.

##STR00001##

In Chemical Formula 1, Z represents any one selected from the group consisting of CN, COOR.sub.11, indanone and 1,3-dioxoindane, wherein R.sub.11 is any one selected from the group consisting of alkyl groups, aryl groups, and substituted or non-substituted heteroaryl groups. The mono-azo dichroic dye compound shows excellent dichroic properties, and has excellent heat resistance and photo-resistance, and thus may be used advantageously for a dye-based polarizing plate.

Sensors for detecting and distinguishing metals in a sample comprise phenol group-containing azo dyes, the phenol group having one hydroxy involved in reversible metal ion binding and a second hydroxy alkylated to an optically transparent substrate. The sensors have utility for detecting chromium, calcium, magnesium, copper, mercury, nickel, zinc, cobalt, manganese, cadmium, lead, tin, aluminum, potassium, sodium, or arsenic ions in a sample.

Provided herein are dyes for detecting and distinguishing metals in a sample, as well as compositions and methods comprising the same.

##STR00001## ##STR00002## ##STR00003##

Disclosed is a mono-azo dichroic dye compound represented by the following Chemical Formula 1, a composition for polarizing plate, a polarizing plate, and an optical device. ##STR00001## In Chemical Formula 1, R.sub.3 represents a substituted or non-substituted heterocyclic group having 1-20 carbon atoms. The mono-azo dichroic dye compound shows excellent dichroic properties, and has excellent heat resistance and photo-resistance, and thus may be used advantageously for a dye-based polarizing plate.

An object of the present invention is to provide a thermal transfer recording sheet that enables images having a wide color gamut, a high chroma, and good lightfastness, in which the degree of catalytic fading is reduced, to be formed. The thermal transfer recording sheet includes a base material and a colorant layer on the base material. The colorant layer includes a yellow dye layer, a magenta dye layer, and a cyan dye layer. The dye layers each include, as a dye, a compound having a specific structure.

A mono-azo dichroic dye compound represented by the following Chemical Formula 1, a composition for polarizing plate, a polarizing plate, and an optical device. ##STR00001## In Chemical Formula 1, Z represents any one selected from the group consisting of CN, COOR.sub.11, indanone and 1,3-dioxoindane, wherein R.sub.11 is any one selected from the group consisting of alkyl groups, aryl groups, and substituted or non-substituted heteroaryl groups. The mono-azo dichroic dye compound shows excellent dichroic properties, and has excellent heat resistance and photo-resistance, and thus may be used advantageously for a dye-based polarizing plate.