This disclosure relates to pyrrolobenzodiazepines (PBDs), in particular pyrrolobenzodiazepine dimers having a C2-C3 double bond and an aryl group at the C2 position in each monomer unit, and their inclusion in targeted conjugates. The differing substituent groups may offer advantages in the preparation and use of the compounds, particularly in their biological properties and the synthesis of conjugates, and the biological properties of these conjugates, specifically cytotoxic activity. In one embodiment, the compound is (S)-2-(4-aminophenyl)-8-(3-(((S)-2-(4-hydroxyphenyl)-7-methoxy-5-oxo-5,11a-dihydro-1H-benzo[ejpyrrolo[1,2-a][1,4]diazepin-8-yl)oxy)propoxy)-7-methoxy-1H-benzo[e]pyrrolo[1,2-a][1.4]diazepin-5(11aH)-one.
