prov:value
| - t at least one of R1, R2, R3, R4, R5, and R6 is other than a hydrogen atom, and provided that at least one Z or Y within the compound is a group of the formula ???NR1R2 or a group of the formula ???NR3R4, R1, R2, R3, R4, R5, R6, and R7 each, independently of the others, is (i) a hydrogen atom, (ii) an alkyl group, (iii) an aryl group, (iv) an arylalkyl group, or (v) an alkylaryl group, and wherein
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