Steric effects in di- and tri-arylmethane dyes. Part XI. Electronic absorption spectra of derivatives of Michler's Hydrol Blue, Crystal Violet, and Malachite Green containing o-trifluoromethyl groups

Abstract

Spectral changes caused by the effects of o-trifluoromethyl groups in Michler's Hydrol Blue, Crystal Violet, and Malachite Green are described and discussed. Pronounced bathochromic shifts of the first bands are observed for the electronically symmetrical dyes. The introduction of a trifluoromethyl group into the 2′-position of Malachite Green brings about a marked conformational change resulting in a hypsochromic shift of the first band. In certain cases, the combined steric and electronic effects of the trifluoromethyl groups are sufficient to shift the equilibrium between dye base and univalent dye cation in acid solution in favour of the former species.