Dyes of the triphenylmethane type as sensor materials for solvent vapours

Summary The formation of highly coloured trityl ions from substituted phthalides can be utilized for the detection of solvent vapours in the air down to nearly ten ppm. These optochemical sensor materials were optimized with respect to their sensitivity, stability, linearity of the response and exclusion of the humidity influence. For this purpose the 4,4,4-substituents at the aromatic rings of the dyes must yield an appropriate carbenium ion stability. Thus even small amounts of absorbed solvent vapours lead to the reduction of the dye concentration in the sensor layers. The largest sensitivity can be achieved by applying dyes with two — N(CH₃)₂ substituents or, instead of one dimethylamino group, the — OCH₃ group at the aryl rings. Further improvements to reduce the sensor response to moisture were possible by introducing into the phthalides large aromatic ring systems with a hydrophobic behaviour such as indolyl.

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Farbstoffe vom Triphenylmethan-Typus als Sensormaterial für LösungsmitteldÄmpfe

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Dedicated to Prof. Dr. Hans Hofmann on the occasion of his 60th birthday