Molecular Nanotube Aggregates of β- and γ-Cyclodextrins Linked by Diphenylhexatrienes

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Science  08 Apr 1994:
Vol. 264, Issue 5156, pp. 249-251
DOI: 10.1126/science.264.5156.249


Linked by strings of diphenylhexatriene (DPH) molecules, β- and γ-cyclodextrins (CDs) can form nanotube aggregates that contain as many as ∼20 βCDs (20 nanometers long) or ∼20 to 35 γCDs (20 to 35 nanometers long). Nanotube formation was indicated in solution, by fluorescence anisotropy and light scattering results, and on graphite surfaces, by scanning tunneling microscopy. Tubes were not observed for the smaller αCDs. Molecular modeling shows that CD cavity size and the rodlike DPH structure are key factors in nanotube formation. Spectra generated by proton nuclear magnetic resonance indicate the inclusion of DPH in the interior of the CDs and formation of nanotubes in βCDs and γCDs only. The photophysical properties of DPH are affected by its arrangement into a one-dimensional array within the CD nanotube, possibly because of exciton formation.