The association of inclusion complexes of cyclodextrins with azo dyes

OrangeII (4) and cyclodextrin (CD) form 2 : 1 and 2 : 2 complexes. The complexes self-associate and microscopy indicates the formation of a fibroid aggregate. In the induced c.d. spectrum, the ^* band of this complex appears at 500 nm in solution, but in the aggregate it changes to aJ-band due to the head-to-tail stacking of4 and aH-band due to its parallel stacking; this indicates that the aggregation expands not only in the direction of the symmetry axis of the CD, but also in the other two dimensions.²H-NMR spectroscopy from deuteron exchange and solvation between the aggregate and deuterium oxide exhibits quadrupole splitting in the region of 0–0.2 KHz. The orientation behavior obtained from this splitting suggests the formation of a liquid-crystaloid substance.¹³C-T ₁ NMR indicates that molecules4 and CD show the sameT ₁ values even at 333 K; this complex behaves like a single molecule. The behaviors of other azo dye-CD complexes are also discussed.DeceasedDedicated to Professor József Szejtli.