Thio indigo

Herz A process for making o-amino thiophenols by heating the hydrochlorides of aromatic amines with sulfur monochloride at 50 to 75°C. The products are used as intermediates in the manufacture of thio-indigo dyestuffs. Invented by R. Hertz in Germany in 1914. 

A number of photochromic systems have been extensively investigated that undergo cis-trans isomerization (indigos, azo compounds) cleavage (spiropyrans), electrocyclic processes (fulgides, 1,2-diarylethenes) [8.229, 8.244, 8.245], For instance, cis-trans isomerization of a thio-indigo derivative allows the reading of pyrene excimer or monomer fluorescence [8.246]. The 1,2-dithienylethene system presents particularly attractive interconversion properties by photoreversible cyc-litation [8.245],... 

The symmetrical dibromoderivative of indigo is the dye called Tyrian purple by the Greeks. It was obtained by them from a certain variety of mollusc. Thio-indigo has a reddish-blue color, it contains two sulphur atoms in place of the NH groups in indigo. 

Several compounds which are known as thioindigo dyes are derived fromm benzo[Z>]thiophene. Thio-indigo 6 itself is made from 2-sulfanylbenzoic acid via benzo[fe]thiophen-3(2//)-one 5 (thioindoxyl) by the following steps (Friedlander 1905) ... 

S -Tetraphenyl-thio-indigo ) red. with alkali acetone 300 9 no detailed A/-data Br 16 ... 

Numbering of substituent positions, see thio-indigo. ) Further small splittings by protons of the ethoxy-groups. ) Further smaE spHt jngs by protons ... 

The optical properties of pigments in the near infrared were studied by Taylor Di Bernardo reported anomalous spectrophotometric behavior of copper phthalocyanine—benzidine yellow mixtures. Brode and Wyman presented the absorption spectra of ten thio-indigo dyes in benzene and chloroform and discussed the effect of irradiation upon their cis-trans equilibria they also presented the spectra of nine of these dyes in H2SO4 in the range 210-800 m/i. 

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