End groups plays very important role to tune the properties and performance of small molecule acceptors. In this study, theoretical analysis was performed to find the reason why two similar molecule differ in end-group showed much different performance in organic solar cells. 1,1-dicyanomethylene-3-indanone based small molecule acceptor (DC-IDT2Tz) showed higher transition dipole moment as compare with malononitrile based small acceptor (MN-IDT2Tz). DC-IDT2Tz showed lower exciton binding energy as compare to MN-IDT2Tz. As well as, DC-IDT2Tz showed lower reorganization energy and higher transfer integral as compare with that of MNIDT2Tz. All the theoretical descriptors are explaining reason behind the higher efficiency of DC-IDT2Tz. Studying theoretical parameters can help to check the performance of organic semi-conductor before synthesis. This work will be helpful for experimental scientists to screen the compounds and to select best one for synthesis.