SYNTHESIS OF CYANINE DYES BY THE CONDENSATION OF  p-DIETHYLAMINOBENZALDEHYDE WITH APPROPRIATE  HETEROCYCLIC COMPOUNDS. PART VIII

Pour new dyes have been prepared by condensing p-diethylaminobenzaldebyde with the methio­dides of 2:4-dimethyl-, 2: 7-dimethyl- and 2-methyl-6-iodo-beazthiazole, and ther optical and other properties examined. Results of previous communications have been collected andi it has been shown that the substitution at the 4.position of the benzthiazole nucleus affords maximum extra-sensitisation. It has also been shown that the substituents at the 4-position fall in the order: EtO- >Me- >Cl,Br- > MeO-> I- with respect to extra-sensitisation.