It has been generallyrecognized that chromophore aggregation quenches fluorescence process.We have observed an opposite phenomenon termed"aggregation-induced emission" (AIE) and identified the restriction of intramolecular rotation (RIR) as the main cause for the AIE effect.Guided by the RIR mechanism,we have developed a wide variety of new AIE fluorogens with emission colors covering the whole visible spectrum,fluorescence quantum yields up to unity,and remarkable susceptibility to multi-photon excitation.