| http://www.w3.org/ns/prov#value | - The preferable diarylmethane and diarylethane are represented by the following general formula: ##STR1## wherein R1 to R5 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R6 is a hydrogen atom or a methyl group, and the total number of the carbon atoms of R1 to R6 is an integer from 1 to 5, inclusive.
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