| http://www.w3.org/ns/prov#value | - Preferably R.sup.1, R.sup.2 and R.sup.3 are each aromatic.Q is a carbon-to-carbon bond or a linking group selected from ##STR5## in which R.sup.4 and R.sup.5 are independently selected from hydrogen, an alkyl group having from 1 to 4 carbon atoms, and an alkenyl group having from 2 to 4 carbon atoms,R.sup.6 is an aryl group having from 6 to 20 carbon atoms, such as phenyl, or an acyl
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