For example, in the absence of readily nitrated groups (for example, in the absence of phenyl groups) at the 3-, 4-, and 5-positions of the oligo-2,6-pyridine moiety of the macrocycles of this invention, i.e., when each of R and Ri is a non-phenyl group such as hydrogen or an alkyl group, a substituent at one X in Structure I comprising a phenyl group can be converted by nitration to a nitrophenyl