Provided is a compound having formula (I): wherein R2 is selected from -C1, -Br and -CN； R1 and R4 are independently selected from H and -F； R631, R632, R641 and R642 are independently selected from -H, -F and substituted or unsubstituted C1-C3 alkyl groups； and R651 and R652 are independently selected from H and substituted or unsubstituted C1-C3 alkyl groups and substituted or unsubstituted phenyl groups； and wherein at least one of R631, R632, R641, R642 and R652 is not -H, or wherein when all of R631, R632, R641, R642 and R652 are -H, R651 is not Me or Et.
