Synthese und Charakterisierung photochromer 2,2′‐Dinitro‐diphenylmethane

Synthesis and Characterization of Photochromic 2,2′‐DinitrodiphenylmethanesPhotochromic methyl‐, amino‐, nitro‐ and formyl‐derivatives of 2,2′‐dinitro‐diphenylmethane 1 are synthesized by nitration of the substituted diphenylmethanes. They react with aromatic aldehydes or activated benzylcompounds respectively to the photochromic compounds 6a, 6b and 5c–5f containing phenyl‐vinylen and phenyl‐azavinylen units. Condensations with corresponding bifunctional compounds yield oligomers, the Knoevenagel‐product is soluble and photochromic.The synthesized 2,2′‐dinitro‐diphenylmethanes are photochromic in solution. The thermal back reaction is described by first order kinetics. Methyl groups decrease and, on the other hand, nitro functions increase the lifetime of the coloured polymethinform.