Colour effects with the Nitrobenzyll Esters of Dimethylaminobenzoic acids

Nitrobenzyl esters of dimethylaminobenzoic acids are strongly coloured in the solid state but not in solution. The operation of electron donor-acceptor interaction within the crystal lattice is indicated. One of the compounds, o-nitrobenzyl m-dimethylaminobenzoate, formed two differently coloured polymorphic modifications.