ethyl or ethyl substituent.This 1-alkyl-4-nitromethylene-quinolane can have the general formula: ##STR1## in which R.sup.1 represents an alkyl group containing 1 to 4 carbon atoms, and each R.sup.2 independently represents a substituent which can be present in a quinolinedye.Examples of substituents which can be represented by each of the substituents R.sup.2 are a hydrogen or halogen atom, e.g. c