Triphenylmethane dyes containing the N-methyl-N-2,2,2-trifluoroethyl group

Analogues of Malachite Green containing terminal N-methyl-N-2,2,2-trifluoroethyl groups have been prepared and their electronic absorption spectra and lightfastness properties determined. The reduced electron donating effect of the fluorinated moiety results in a hypsochromic shift of lambda(max)(x) in the unsubstituted analogue. Meta- and par a-substituents in the phenyl ring modify the position of the x-band which can be correlated linearly with the appropriate Hammett sigma constant. In contrast to the Malachite Green series, substitution by methyl groups ortho to the terminal amino moieties produces a small red shift of the first frequency band. The steric deconjugation of the more weakly donating N-methyl-N-2,2,2-trifluoroethyl group is dominated by the electron release of the methyl groups at the 'active' 3'- and 3 "-positions. Some of the analogues exhibit enhanced photostability relative to the corresponding Malachite Green derivatives. (C) 1999 Elsevier Science Ltd. All rights reserved.