Adduct formation between alpha-, beta-, gamma-, and (permethyl)gamma-cyclodextrins (CDs) on the one band and 1,6-diphenyl-1,3,5-hexatriene (DPH) on the other was studied by fluorescence spectroscopy in a DMF/water mixed solvent. The four complexes, CD-DPH, were found to exhibit remarkable differences in their structures. Thus, while the alpha- and beta-homologues form 1/1 complexes with DPH, gamma-homologue forms nanotubes involving ca. 30 cyclodextrin- units and an unknown number of DPH molecules. If, however, the hydrogens of all the OH groups in the gamma-cyclodextrin are replaced by CH3 groups, nanotubes do not form. Also, when the alkalinity of an aqueous solution, in which gamma-CD and DPH have formed nanotubes, is increased above pH = 12, the nanotubes break down. Moreover, nanotube formation does not occur also when DPH is replaced by certain of its derivatives, very similar to it in structure and rodlike in shape.