Steric effects in di- and tri-arylmethane dyes. Part X. Electronic absorption spectra of bridged derivatives of malachite green and crystal violet

Abstract

The isopropylidene group has been introduced singly and doubly into ortho-positions of Malachite Green and Crystal Violet in order to determine molecular conformation. The electronic absorption spectra of these dyes are discussed with particular reference to their bearing on intensity variations of the first band of ortho-derivatives of Malachite Green. The introduction of two isopropylidene bridges into Malachite Green and Crystal Violet produces considerable bathochromic shifts that can only be attributed to distortion of the aryl nuclei.

Molecular planarity enforced by introduction of a 4,2′-isopropylidene bridge into 2,7-bisdimethylamino-10-(4′-dimethylaminophenyl)anthracene stabilises the cation formed by C₉-protonation of the anthracene nucleus so that in 98% acetic acid about 60% of the amine is so protonated.