Formation mechanism and photo physical behaviors of Pyrene-Methyl-beta-cyclodextrin complex at excited state

Sarli S. E. , Ay U.

INORGANIC CHEMISTRY COMMUNICATIONS, cilt.114, 2020 (SCI İndekslerine Giren Dergi) identifier identifier


Structural characterization of the Pyrene-Methyl-beta-cyclodextrin (Py-Me-beta-CD) complex, obtained in aqueous medium, was carried out through Fourier Transform Infrared spectroscopy (FTIR), X-ray diffractometry (XRD), H-1 NMR and two-dimensional correlated spectroscopy (2D COSY). Thermal characterization of the Py-Me-beta-CD complex was performed with differential scanning calorimetry (DSC) and thermogravimetry (TG). Gibbs free energy and excited singlet state energy values of the complex were calculated. The stoichiometry of the complex was determined to be 1:2 by the Benesi-Hildebrand method. The complex binding constant (Kb), which was 1.5 x 10(11) M-1, indicated a strong inclusion complex. Both thermal and XRD analyzes showed that the crystallinity of the pyrene decreased and its thermal stability increased as a result of complex formation. The most obvious quenching effect in the transition metals (cobalt, iron, zinc, copper, manganese and nickel) was obtained with iron. Calculated Stern-Volmer constant (K-sv) and the quenching activation energy (E-a) values showed that iron interacted with the complex differently. The lifetime (tau) and bimolecular quenching rate constant (k(q)) calculations pointed to diffusion controlled dynamic quenching for the metals, other than iron. In addition, with the energy band calculations made, it was shown by means of Tauc plots, that electron transfer was made to iron and manganese metals from the complex fluorophore group, as part of the quenching mechanism. The value of the activation energy for iron indicated a weakly bound encounter complex formation.