Fast (hetero)aryl-benzothiazolium ethenes photoswitches activated by visible-light at room temperature

• Synthesis of new ethenyl benzothiazolium dyes linked to different (hetero) aromatic systems.
• The benzothiazolium dyes show thermally reversible photochromic properties.
• The trans–cis photoisomerization can be performed with visible light in water.
• The forward (photo) and back (thermal) E-Z switching cycle takes 4 min.

A series of novel photochromic cationic stilbenes dyes bearing different aromatic systems were easily synthesized from (hetero)aromatic aldehydes. The photoisomerization of the double bond can be achieved through irradiation with ultraviolet or visible light, for few seconds, leading to the Z isomers that return much faster to the initial state than common stilbenes. Benzothiazolium dyes with electron donating substituents exhibited very fast thermal back reactions (<1 s). Pyrrole-benzothiazolium dye showed a higher lifetime of the Z isomer, in different solvents, including water (0.45–7.1 min). This cationic diarylethene can be switched between the E-Z states using visible light, in few minutes at room temperature, with a noticeable change in the visible spectrum.

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