| http://www.w3.org/ns/prov#value | - r heteroaromatic rings with or without deuterium, and R1 and R2 are independently each selected from the group consisting of hydrogen, deuterium, substituted or unsubstituted alkyl, alkoxyl, aryl and heteroaryl, or halogen, wherein D represents deuterium and n is an integer greater than 3.
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