prov:value
| - R1, R2, R3, and R4 are independently select from the group consisting of an aryl group, alkyl group, alkoxy group, aryloxy group, amino group and halogen atom, at least one of R1, R2, R3, and R4 is an aryl group; r1, r2, r3, and r4 are independently 0 or an integer of 1 to 5, the sum of r1, r2, r3, and r4 is an integer of at least 1; R5 and R6 are independently selected from the group consisting o
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