The aggregation-induced emission (AIE) properties of a systematic series of naphthalene diimides (NDIs) varying the chain length at the imide positions have been studied. A solvophobic collapse of NDI units through the flash injection of THF NDI solutions in sonicating water triggers the formation of stable suspensions with enhanced fluorescence emissions. Shorter chains favor the π−π stacking of NDI units through H-aggregation producing a strong AIE effect showing remarkably high quantum yields that have not been observed for non core-substitued NDIs previously. On the other hand, NDIs functionalized with longer chains lead to more disordered domains where π−π stacking between NDI units is mainly given by J-aggregation unfavoring the AIE effect.