In order to figure out the effects of terminal groups on phase transitions and birefringence, we performed a comparative study for non-fluorinated and centrally fluorinated liquid crystalline 1,4-bis(phenylethynyl)benzene molecules with the same tail length of heptyl, hexyloxy, hexylthio groups at both para positions. These molecules showed remarkable effects of the terminal groups to the phase transitions. The birefringence values at close temperatures, as well as an order parameter (S) = 1 for a fluorinated family, are in the following order of alkylthio > alkoxy > alkyl analogues, corresponding to their polarizabilities.