Femtosecond time-resolved measurements are conducted on two aggregation-induced emissive molecules: cyano-substituted oligo-(alpha-phenylenevinylene)-1,4-bis(R-cyano-4-diphenylaminostyryl)-2 ,5-diphenylbenzene (CNDPASDB) and cyano-substituted oligo(p-phenylenevinylene) (CNDPDSB). By examining whether the photoluminescence decay is accompanied by ground state bleaching recovery, different mechanisms for their low emission in solution state are revealed. For CNDPASDB with donor/acceptor group, the interconversion from the highly emissive local excited state to the relatively dark intramolecular charge transfer state results in the low emission. For CNDPDSB without electron donor group, there is no intermediate dark state, and the low emission is caused by the efficient vibrational/torsional nonradiative relaxation.