Azo dye/cyclodextrin: New findings of identical nanorods through 2:2 inclusion complexes

• AAB and GBC dyes form 2:2 barrel type inclusion complexes.
• AAB/CD and GBC/CD inclusion complexes form nanorod structure.
• Intermolecular hydrogen bonding plays a crucial role in the formation of nanostructure.
• Nanosecond time-resolved studies indicated that AAB/GBC have fast life time in water, and slow life time in CDs.

Inclusion complexation behavior of 4-aminoazobenzene (AAB) and 4-amino-2,3′-dimethyl azobenzene (GBC, fast grant GBC) with α- and β-cyclodextrins (α-CD, β-CD) is analyzed by scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscopy, differential scanning calorimetry, powder X-ray diffraction, and proton nuclear magnetic resonance spectroscopy techniques. Transmission electron microscope analysis suggests that identical nanorods formed in AAB/CD inclusion complexes while different dimension nanostructures were observed in GBC/CD inclusion complexes. The nanostructures confirmed that the ratio of 2:2 (guest:host) inclusion complex has been developed to a miniature nanorod. Nanosecond time-resolved fluorescence studies indicated that AAB/GBC have fast life time in water, whereas slow life time in CDs corresponds to a higher-order structure of 2:2 complexes. Thermodynamic parameters and binding affinity of the inclusion complex formation were determined and discussed. van der Waals interactions are mostly responsible for enthalpy-driven complex formation of AAB and GBC with cyclodextrins.