Nanostructures formed by cyclodextrin covered aminobenzophenones through supramolecular self assembly

Area of Science:

• Supramolecular Chemistry
• Nanomaterials Science
• Materials Chemistry

Background:

• Cyclodextrins (CDs) are versatile cyclic oligosaccharides utilized in supramolecular chemistry.
• Aminobenzophenones (ABPs) are organic molecules with potential applications in various fields.
• Supramolecular self-assembly offers a pathway to create complex nanostructures from simple building blocks.

Purpose of the Study:

• To investigate the formation and characterization of nanostructures self-assembled from cyclodextrin (α and β) and aminobenzophenone (2-ABP and 3-ABP) inclusion complexes.
• To elucidate the role of intermolecular hydrogen bonding in directing the self-assembly process.
• To explore the photophysical properties and molecular interactions within the formed nanostructures.

Main Methods:

• Absorption, fluorescence, and time-resolved fluorescence spectroscopy.
• Microscopy techniques including Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM).
• Spectroscopic and thermal analysis: FT-IR, Differential Scanning Calorimetry (DSC), Powder X-ray Diffraction (PXRD), and ¹H NMR.
• Computational analysis using semiempirical PM3 calculations for thermodynamic parameters.

Main Results:

• Self-assembly of 3-aminobenzophenone/cyclodextrin (3ABP/CD) inclusion complexes resulted in layer-by-layer nanosheets and nanoribbons.
• 2-aminobenzophenone/α-cyclodextrin (2ABP/α-CD) complexes formed hierarchical thread structures.
• β-cyclodextrin complexes (2ABP/β-CD) exhibited a nanobrick structure.
• Intermolecular hydrogen bonds (HO⋯H, NH2⋯O, H2N⋯H) were identified as key to nanostructure formation.
• Spectral changes indicated the formation of 1:1 inclusion complexes and confirmed Excited-State Intramolecular Proton Transfer (ESIPT) and Intramolecular Charge Transfer (TICT) phenomena.
• Thermodynamic parameters (ΔH, ΔG, ΔS) for ABP molecules and their inclusion complexes were determined.

Conclusions:

• Cyclodextrin-based supramolecular self-assembly provides a tunable platform for creating diverse nanostructures (nanosheets, nanoribbons, threads, nanobricks).
• The type of cyclodextrin (α- or β-) significantly influences the resulting nanostructure morphology.
• Intermolecular hydrogen bonding plays a crucial role in directing the self-assembly and stabilizing the nanostructures.
• Photophysical studies reveal the presence of ESIPT and TICT, offering insights into the electronic properties of the ABP molecules within the nanostructures.
• Thermodynamic calculations provide quantitative data on the stability and interactions involved in the inclusion complex formation.