Synthesis of 4-Anisidine/Cyclodextrin Covered Copper Nanomaterials and pH-Dependent of 4-Anisidine–Cyclodextrin Inclusion Complexes

The spectral properties of the copper–4-anisidine–cyclodextrin (Cu: 4AS: CD) nanomaterial were examined using absorption, fluorescence, time-resolved fluorescence, SEM, DSC, FTIR, XRD, ¹H NMR, and molecular modeling techniques. The distinct spectral variations observed for 4AS upon adding α-CD and β-CD at different pH values indicate that the resulting inclusion complexes adopt different structural geometries. While 4AS exhibits a single emission maximum in all solvents and in α-CD solutions, dual emission bands are observed in β-CD. The confined geometry of the α-CD cavity likely restricts the free rotation of the amino or methoxy substituents of 4AS, suppressing the formation of the intramolecular charge-transfer (ICT) state and thereby enhancing the normal emission. The calculated HOMO–LUMO energy gap, total energy, free energy, enthalpy, entropy, dipole moment, and zero-point vibrational energy of the CD: 2AP complex differed significantly from those of the isolated 4AS, α-CD and β-CD molecules, and both the vertical and horizontal bond lengths between the amino and methoxy groups are smaller than the β-CD cavity size confirming the formation of an inclusion complex. SEM images and EDX analysis of the Cu: 4AS: β-CD nanomaterial reveal the presence of copper. In the FTIR spectra, several characteristic peaks disappear in the Cu: 4AS: CD nanoparticles, indicating strong interactions between 4AS and copper nanoparticles. The ¹H NMR spectra show both upfield and downfield shifts of 4AS proton signals support strong coordination of 4AS with copper in the CD-based nanomaterials.