Synthesis of Ag: 4-Aminophenol: Cyclodextrin Nanomaterials and 4AP: CD Inclusion Complexation at Different pH

Inclusion complexation of 4-aminophenol (4AP) with α-CD and β-CD at pH ~2, pH ~7, and pH ~11 was investigated using UV-visible, steady-state and time-resolved fluorescence measurements, along with molecular modeling studies. Ag: 4AP: CD nanomaterials were synthesized and characterized by SEM, DSC, FTIR, XRD, and sup1/supH NMR analyses. Increasing CD concentrations induced dual emission in the excited state. The changes in emission intensity at pH ~7 and the structured emission observed at pH ~11 indicate the formation of excimers in the excited state, while ground-state dimers are not formed due to the ionization of amino and hydroxyl groups. The lifetimes of the inclusion complexes were longer than that of the free 4AP molecule. The geometrical restriction of the α-CD cavity likely limits the free rotation of the amino and hydroxyl groups, thereby enhancing the intensity of the IPT emission. The calculated HOMO-LUMO energy gap, total energy, free energy, enthalpy, entropy, dipole moment, and zero-point vibrational energy of the CD: 4AP complex differed significantly from those of the isolated 4AP, α-CD and β-CD molecules, and both the vertical and horizontal bond lengths between the amino and hydroxy groups are smaller than the β-CD cavity size confirming the formation of an inclusion complex. SEM-EDX analysis confirmed the presence of 40.4% carbon, 50.4% oxygen, and 9.2% silver in the nanomaterials. DSC, FTIR, XRD, and sup1/supH NMR results collectively support the successful formation of Ag: 4AP: CD nanomaterials.