Nucleoside analogs comprising polyfluorinated benzene, pyrrole, pyridine, indole, isoindole, or benzoimidazole rings are shown to provide for selective base pairing with self, or other polyfluorinated analogs, in preference to native nucleic acid bases. The analogs of the invention stabilize the stacking of helices, and increase hydrophobicity when introduced into an oligonucleotide.