Aromatic dimethylidyne compounds

An aromatic dimethylidyne compound of the formula:

• ##STR54## wherein X and Y may be the same or different and are each an alkyl group having 1 to 4 carbon atoms, phenyl group, a substituted phenyl group, a cyclohexyl group, a substituted cyclohexyl group, a naphthyl group, a substituted naphthyl group, a pyridyl group or a substituted pyridyl group, wherein the substituent is an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a phenyl group, and each substituted group may be substituted by a plurality of said substituent groups, and --Ar'-- is ##STR55##