. " or an alkyl group (including linear, branched, substituted, and unsubstituted alkyl groups), in one embodiment with at least 1 carbon atom, and in one embodiment with no more than about 3 carbon atoms, although the number of carbon atoms can be outside of these ranges, R4 and R???4 each, independently of the other, is a hydrogen atom, a fluorine atom, an alkyl group (including linear, branched, s" . . .