Methods and compositions are provided for forming complexes between dsDNA and novel DNA-binding polymers comprising N-terminal thiophene-containing moieties which exhibit selectivity for T-A base pairs. By appropriate choice of target sequences and DNA-binding polymers, complexes comprising polymer-DNA are obtained with high association constants. The formation of complexes can be used for identification of specific dsDNA sequences, for inhibiting gene transcription, and as a therapeutic for inhibiting proliferation of undesired cells or modulation of expression of specific genes.