c rings of stilbene and fluorene or in the case where the aromatic rings are linked by groups such as amide groups or ester groups; or (c) the free rotation of the aryl allyl ether group(s) on the aromatic ring(s) of the aryl allyl ether structure is being restricted due to the presence of at least one or more substituents on the aromatic ring(s) ortho to the aryl allyl ether group(s), that is, th