Synthesis of Copper–2,5-dimethylphenol –Cyclodextrin Nanomaterials and pH-Dependent of 2,5-dimethylphenol –Cyclodextrin Inclusion Complexes

Absorption, emission, and time-resolved fluorescence maxima of 2,5-dimethylphenol (25DMP) were examined in various solvents, as well as in α-CD and β-CD solutions at pH ~2, pH ~7, and pH ~11. The corresponding nanomaterials were synthesized and characterized using SEM, DSC, FTIR, XRD, and ¹H NMR analyses. At pH ~1 and pH ~7, the absorption/emission maxima and overall spectral profiles of 25DMP in α-CD and β-CD solutions were similar, but differed markedly at pH ~11, suggesting the presence of at least two distinct types of inclusion complexes. PM3 calculations indicate that 25DMP is more deeply embedded within the non-polar region of the β-CD cavity than in α-CD. Solvatochromic studies further show that the absorption and emission maxima of 25DMP display negligible shifts from cyclohexane to water. The fluorescence lifetimes of the 25DMP: CD complexes were greater than those of free 25DMP. The calculated HOMO–LUMO energy gap, total energy, free energy, enthalpy, entropy, dipole moment, and zero-point vibrational energy of the CD: 25DMPcomplex differed significantly from those of the isolated 25DMP, α-CD and β-CD molecules, and both the vertical and horizontal bond lengths between the methyl and hydroxy groups are smaller than the β-CD cavity size confirming the formation of an inclusion complex. SEM images along with DSC, FTIR, XRD, and ¹H NMR data reveal clear differences between Cu nanoparticles, free 25DMP, and the Cu: 25DMP: α-CD and Cu: 25DMP: β-CD nanomaterials. SEM-EDX analysis confirms the presence of 49.95% carbon, 44.03% oxygen, and 3.98% nano-Cu in the prepared nanomaterials.