Three perylenetetracarboxylic diimide (PDI) derivatives comprising a different number of hydrophobic alkoxy chains at one imide nitrogen were synthesized. The aggregation behavior of this series of compounds was investigated by UV-vis absorption and emission spectra. The results indicated that large number of hydrophobic alkyl chains at one end of the PDI molecules can induce significant aggregation in solution, but without obvious ground state interaction between the PDI aromatic cores. The aggregation behavior of this series of compounds in solid state was studied by absorption and IR spectra as well as X-ray diffraction (XRD) experiments. The morphology of the solid aggregates was investigated by scanning electronic microscopy (SEM). With an increase of the number of alkyl chains at one end of these PDI molecules, the aggregation mode varies from H type to J type, while the morphology of the solid aggregates changes from small bending belts to long ordered wires. This research demonstrated that one can control the aggregation mode, the order, and the morphology of the molecular aggregates by changing the number of alkyl chains. This information can be useful in the design of novel organic materials which exhibit molecular aggregation. (C) 2010 Elsevier Inc. All rights reserved.