The rectifying properties of seven molecular junctions sandwiched between periodic semi-infinite electrodes were studied using the non-equilibium Green's function method combined with density functional theory. The effects of proportion and location of pyrimidinyl for modulation of rectification have been investigated. Calculated current-voltage curves showed that the change of the proportion of pyrimidinyl has a strong effect on the value of the rectification ratio and the change of the location of pyrimidinyl leads to an inversion of rectification to a certain degree. The rectification ratio of dipyrimidinyl-diphenyl was compared with the results from previous investigations. (C) 2016 Elsevier B. V. All rights reserved.