We have studied the size effect of the homologues of the alpha,omega-diphenylpolyenes series, with two, three and four double bonds, on the formation of nanotubes with gamma-cyclodextrin. The data show that only the two longest polyenes facilitate the formation of tubular structures when mixed with the gamma-cyclodextrin in the appropriate solvent, while the average length of these nanotubes increases with increasing size of the diphenylpolyenes. Using computer simulations, we have examined the processes by which nanotubes form, and from computer fits we have determined the various binding constants, some with extremely large values, involved in the formation of these supramolecular structures.