1,2,3‐Triazabutadienes. XXII. Photochemistry of 1‐(Carbmethoxy‐aryl)‐ and 1‐(Carboxy‐aryl)‐3‐(3‐alkyl‐benzthiazolinyliden‐(2))‐triazenes as potential CEL‐dyes 1‐(Carbmethoxy‐aryl)‐3‐(3‐alkyl‐benzthiazolinyliden‐(2))‐triazenes (ester‐triazenes) (1) were synthesized by coupling of substituted 3‐alkyl‐2‐imino‐benzthiazolines‐(1,3) with 2‐, 3‐ and 4‐carbmethoxy‐benzenediazonium salts. The Z‐isomers obtained can be transformed into the E‐isomers 2 photochemically or by heating. In the presence of acids the E‐ester‐triazenes are protonated. From the E‐ester‐triazenes the potassium‐salts (4) can be produced by alkaline ester hydrolysis. With hydrochloric acid the E‐triazene‐potassium salts (4) can be transformed into the protonated (at the N(1)‐Atom) E‐acid‐triazenes (5). Their photochemical properties are identical with those of the protonated E‐ester‐triazenes (3). The 1‐(carboxy‐aryl)‐3‐(3‐alkyl‐benzthiazolinyliden‐(2))‐triazenes (E‐acid‐triazenes) (6) can be obtained from the protonated derivates by deprotonation in the presence of water. The photochemical behaviour of the E‐acid‐triazenes (6) and of the E‐triazene‐potassium‐salts (4) depends on the position of the carboxy‐group (2‐position: photolysis, 3‐ and 4‐position: photoisomerization). The uv/vis‐spectroscopical and photochemical properties of the triazene‐derivates in solution and in polymeric layers are discussed.

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