A phosphorus ester oligomer having structure (I) wherein A can be the same or different in each monomeric unit and each is independently selected from the group consisting of oxygen, sulfur, lower alkyl, alkyl- or aryl-substituted amino and aminoalkyl; B1 and B2 can be the same or different and each is independently selected from hydrogen, lower alkyl, a labelling group, a protecting group, a phosphoramidate or a phosphomonoester; R1 can be the same or different in each monomeric unit, and in at least one of the non-nucleotide monomeric units, R1 is independently selected from the group consisting of a condensation product of (i) a non-vicinal diol attached to a hydrogen bond donor functionality; (ii) a hydrogen bond acceptor selected from an ether, a purine or pyrimidine substituted 1,2-diol or a disubstituted heterocycle; (iii) a non-vicinal diol attached to a hydrophobic functionality or a vicinal diol attached to an aliphatic or alicyclic hydrophobic functionality; (iv) a diol attached to a ring substituted anionic functionality and (v) a cationic moiety attached to a non-vicinal or alicyclic diol, any of which can further include a detectable label, and n is at least one. Preferred R1 moieties include condensation products of heterocyclic diols, alicyclic diols, and polycyclic diols. Also the non-nucleotide monomers thereof, combinatorial library mixtures of the oligomers and the use of the oligomers as selective target-binding compounds.