Aggregation-induced emission enhancement characteristics of naphthalimide derivatives and their applications in cell imaging

Novel naphthalimide derivatives (NIM) with donor–acceptor architecture were successfully constructed and their unique fluorescent properties were investigated. In particular, the fluorescence intensities of 4-methoxystyrene substituted NIM-1 were solvent independent and its quantum yields varied from 0.4 in toluene to 0.52 in MeOH. However, 4-(N,N-diphenylamino) styrene substituted NIM-2 and 4-nitrostyrene substituted NIM-3 exhibited low luminescence in dilute solutions but were efficiently fluorescent under conditions of molecular aggregation. NIM-2 showed strong solid fluorescence with a longer wavelength emission and larger Stokes shift. In addition, NIM-3 showed unexpected blue-green fluorescence due to the formation of fluorescent organic nanoparticles (FONs) under mixed solution. These two cases were ascribed to the aggregation-induced enhanced emission (AIEE) effects and which can also reasonably explain the bright cellular images observed when cells were incubated with NIM-2 and NIM-3. Furthermore, compound NIM-2 can be used to recognize cancer cells owing to its subcellular behaviour.