prov:value
| - In formula (I), R1, R2, R3, and R4 each are a substituted or unsubstituted aryl or alkenyl group; R5, R6, R7, and R8 each are hydrogen; at least two of R1 to R4 are aryl groups which are at least bicyclic, aryl groups having aryl, amino, alkenyl, aryloxy or heterocyclic groups as substituents, or alkenyl groups, and when at least two substituents are monocyclic aryl groups, they further have subst
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