Photoswitching of ortho-Aminated Arylazopyrazoles with Red Light.

Bidirectional photoswitching of arylazopyrazoles with visible light is enabled by substitution with pyrrolidine and piperidine in the ortho-position of the phenyl ring. The absorption maxima were red-shifted and the molar absorption coefficients in the visible range increased significantly, allowing the use of blue light (λ = 465 nm) for the E → Z isomerization and red light (λ = 600 nm) for the Z → E isomerization. N-Methylation of the pyrazole leads to an excellent thermal stability of the Z isomer.