Watching the Conformational Changes of Maleonitriledithiolate Chromophores Inside the Inclusion Complexes with Cyclodextrins: Probed by ICD Spectra and DFT Calculations

Photo-controlled order-to-order host-guest self-assembly transfer for an afterglow effect with water resistance

Due to the general incompleteness of photochemical reactions, the photostationary structure in traditional photo-controlled host-guest self-assembly transfer is usually disordered or irregular. This fact readily affects the photoregulation or improvement of related material properties. Herein, a photoexcitation-induced aggregation molecule, hydroxyl hexa(thioaryl)benzene (HB), was grafted into β-cyclodextrin to form a host-guest system. Upon irradiation, the excited state conformational change of HB can drive an order-to-order phase transition of the system, enabling the transfer of the initial linear nanostructure to a photostationary worm-like nanostructure with orderliness and crystallinity capability. Along with the photoexcitation-controlled phase transition, an afterglow effect was obtained from the films prepared by doping the host-guest system into poly(vinyl alcohol). The afterglow effect had a superior water resistance, which successfully overcame the general sensitivity of doped materials with the afterglow effect to water vapor. These results are expected to provide new insights for pushing forward chemical self-assembly from the light perspective, towards materials with superior and stable properties under light treatment.

Inclusion complexes of cypermethrin and permethrin with monochlorotriazinyl-beta-cyclodextrin: a combined spectroscopy, TG/DSC and DFT study

The suitable size hydrophobic cavity and monochlorotriazinyl group as a reactive anchor make MCT-β-CD to be widely used in fabric finishing. In this paper, the inclusion complexes of monochlorotriazinyl-beta-cyclodextrin (MCT-β-CD) with cypermethrin (CYPERM) and permethrin (PERM) are synthesized and analyzed by TG/DSC, FT-IR and Raman spectroscopy. TG/DSC reveals that the decomposed temperatures of inclusion complexes are lower by 25-30 °C than that of physical mixtures. DFT calculations in conjunction with FT-IR and Raman spectral analyses are used to study the structures of MCT-β-CD and their inclusion complexes. Four isomers of trisubstituted MCT-β-CD are designed and DFT calculations reveal that 1,3,5-trisubstituted MCT-β-CD has the lowest energy and can be considered as main component of MCT-β-CD. The ground-state geometries, vibrational wavenumbers, IR and Raman intensities of MCT-β-CD and their inclusion complexes were calculated at B3LYP/6-31G (d) level of theory. Upon examining the optimized geometry of inclusion complex, we find that the CYPERM and PERM are inserted into the toroid of MCT-β-CD from the larger opening. The band at 1646 cm(-1) in IR and at 1668 cm(-1) in Raman spectrum reveals that monochloroazinyl group of MCT-β-CD exists in ketone form but not in anion form. The noticeable IR and Raman shift of phenyl reveals that these two benzene rings of CYPERM and PERM stays inside the cavity of MCT-β-CD and has weak interaction with MCT-β-CD. This spectroscopy conclusion is consistent with theoretical predicted structure.

Theoretical study on β-cyclodextrin inclusion complexes with propiconazole and protonated propiconazole

The synthesis of the β-cyclodextrin/propiconazole nitrate inclusion complex and the advantages of the encapsulation of this drug were recently reported, but the experimental data only partially revealed the structure of the supramolecular complex due to the limitations in understanding the intermolecular association mechanism. The present work describes the equilibrium molecular geometries of β-cyclodextrin/propiconazole and β-cyclodextrin/protonated propiconazole, established by the AM1 and PM3 semi-empirical methods. The affinity between different parts of the guest molecule and the cyclodextrin cavity was studied considering that propiconazole possesses three residues able to be included into the host cavity through primary or secondary hydroxyl rims. The results have revealed that the most stable complex is formed when the azole residue of the propiconazole enters the cavity of the cyclodextrin through the narrow hydroxyl's rim.

Photophysical properties of 7-(diethylamino)coumarin-3-carboxylic acid in the nanocage of cyclodextrins and in different solvents and solvent mixtures

The photophysical properties of 7-(diethylamino) coumarin-3-carboxylic acid (7-DCCA) were studied in cyclodextrins (α, β, γ,-CDs), different neat solvents and solvent mixtures by using steady state absorption, emission and time-resolved fluorescence spectroscopy. We have observed that with gradual increase in concentration of β-CD the fluorescence quantum yield and lifetime decreased in a regular pattern whereas with gradual increase in concentration of γ-CD the fluorescence quantum yield and lifetime gradually increased. With addition of urea, the fluorescence quantum yield and lifetime of 7-DCCA in CDs increased. Binding constant calculation shows that 7-DDCA forms 1:1 complex with β-CD and with γ-CD it forms 1:1 and 1:2 (guest:host) inclusion complex. We proposed that the dye molecule formed capping complex with β-CD by means of hydrogen bonding and after addition of urea the hydrogen bonding network broke down and part of dye molecule entered inside the cavity of β-CD. The photophysics of 7-DCCA was studied in dioxane-water mixture and ethylene glycol-acetonitrile mixture to know the effect of polarity and viscosity of the media. The photophysics of 7-DCCA was also studied in different neat solvents. It was found that the photophysics of 7-DCCA depended on the structural feature of the solvents and solvent mixtures.