H H ##STR55##46 1 1 H CH3 ##STR56## In the phosphonic acid ester of formula [II] which serves as anintermediate for synthesizing the pyrene-ring-containing olefin compoundof formula [I], R1 is an alkyl group having 1 to 4 carbon atoms.Specific examples of the alkyl group are methyl group, ethyl group,propyl group, isopropyl group, n-butyl group, iso-butyl group,