A series of C3-symmetric trialkanecarboxamido derivatives was synthesized via a triphenylmethane derivative. The triamides with short alkyl chains (1–6 carbons) crystallized as either prisms or plates, whereas those with long alkyl chains (7–11 carbons) formed gel-like objects composed of fibrous crystals with 100-nm diameters. A discontinuity as a function of alkyl chain length was also observed for the melting points, the vibrational frequencies of the amide groups, and the powder X-ray diffraction patterns of the triamides. On the basis of analysis of the crystal structures of two of the compounds, we make some proposals about the molecular packing and the local structure of the molecular assembly. Our results suggest that there were critical differences in inter-core interactions and in the hydrogen-bonding network, depending on the length of the alkyl chains. We interpret the drastic change in morphology brought about by the tuning of the chain length as a consequence of a change in the mode of molecular assembly.