Abstract: Compositions for transfecting a nucleic acid molecule into a cell are described. Each composition includes at least one benzimidazole or benzotriazole compound of general formula (II): in which the benzimidazole or benzotriazole ring is substituted at a ring nitrogen by a graft cationic polymer P+ that is a linear or branched polyethyleneimine (PEI) via a —CH2—(CH2)m—CO— linker, where m is 1-3. The remaining ring positions can be unsubstituted or substituted by alkyl, alkoxy, aryl, or related groups. The compositions can further include a nucleic acid molecule together with an acceptable excipient, buffering agent, cell culture medium, or transfection medium, and are useful for in vitro or ex vivo gene delivery with high transfection efficiency and reduced cytotoxicity.