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