Synthesis and electronic absorption spectra of some novel methoxy half-analogs of Malachite Green and Brilliant Green

Abstract

In this work, various series of triarylmethane dyes containing one or more terminal methoxy substituent together with a variable tertiary amino group have been synthesized. The effects of electron-donating and electron-withdrawing groups have been systematically examined and electron absorption spectra of dyes determined. The absorption bands of the methoxy half-analogues of Malachite Green and Brilliant Green show pronounced hypsochromic shifts together with reduction in intensity owing to the inherent electronic asymmetry of the system. The corresponding dye bases are incompletely ionized in acid solution. Julolidine and Kairoline analogues of these dyes produce further hypsochromic shifts of both visible absorption bands in accordance with enhanced conjugation of the terminally bridged substituents. Crowding substituents at the central carbon atom in the series of methoxy half-analogues produce hypsochromic shifts of the absorption bands owing to the inherent electronic asymmetry; bond order alteration throughout the system ensures that crowding effects are minimized by rotation about essential single bonds.