TD-DFT study on the fluoride and copper ion sensing mechanism of pyrene N(4) phenyl thiosemicarbazone

Abstract

The interaction between pyrene thiosemicarbazide with fluoride and copper ion have been theoretically investigated by DFT and TDDFT methods. For the complex PyPTSC-F, the geometrical parameter difference in the ground state and excited state is the reason behind the fluorescence quenching by the photoinduced electron transfer (PET) process. The intermolecular proton transfer (IPT) causes the colorimetric signalling of PyPTSC for F− and Cu2+. The strong electronegativity of fluoride ion makes the intermolecular hydrogen bond with PyPTSC via NH⋯F in the ground state. And the proton transfer was occurring at the excited state and seen the hydrogen bond via N⋯HF, which has been confirmed by natural bond orbital (NBO) analysis and the potential energy curve of ground state and excited state for the function of the NH bond. For the fluoride sensing process has a moderate transition barrier of 15.16kcalmol−1, the calculated vertical excitation energies in the ground state and the first singlet excited state reproduced the experimental UV–Vis absorbance and fluorescence emission spectra as well. The ICT mechanism for copper ion sensing was also confirmed with TD-DFT calculations.