Acrylates, for example ethyl ??-cyano-??,??-diphenylacrylate or isooctyl ??-cyano-??,??-diphenylacrylate, methyl ??-carbomethoxycinnamate, methyl ??-cyano-??-methyl-p-methoxy-cinnamate or butyl ??-cyano-??-methyl-p-methoxycinnamate, methyl ??-carbomethoxy-p-methoxycinnamate and N-(??-carbomethoxy-??-cyanovinyl)-2-methylindoline.