Self-Assembly of a β-Cyclodextrin Bis-Inclusion Complex into a Highly Crystalline Fiber Network. An Effective Strategy for Null Aggregate Design.

The present work deals with the tight molecular packing of a bis-inclusion complex into rigid, 1D nanofibers. The bis-adamantane (AD) linked anthracene derivative AD-AN-AD readily formed the β-CD bis-inclusion complex, β-CD⊂AD-AN-AD⊃β-CD, which spontaneously assembled into a nanofiber network. The wide angle X-ray scattering pattern of the dried nanofibers indicated that these are highly crystalline in nature. Spectroscopic data of the aggregate are identical to those of the monomeric species, suggesting that the aggregate is not a regular H- or J-aggregate. We propose that the nanofibers constitute another example of the recently proposed class of "null" aggregates, based on the crystal structure and molecular packing in compound 3, which is the precursor of AD-AN-AD. The molecular packing in 3 actually provides a strategy for the design of null aggregates. We propose that the nanofibers are formed from null aggregates of β-CD⊂AD-AN-AD⊃β-CD, wherein the anthracene moieties are twisted in the range of 60-72°, and this assignment is in line with the spectroscopic studies and NMR titration experiments.