TD-DFT investigation on anion recognition mechanism of anthraldehyde-based fluorescent thiosemicarbazone derivatives

Abstract

The mechanism of host-guest interaction of receptors towards uoride ion has been investigated using computational methods. To distinguish the effect of aromaticity in host-guest interaction, we investigated unsubstituted (ATSC) and phenyl substituted (APTSC) anthracene thiosemicarbazones towards different ions. In the ground state of receptor-uoride complex, the added uoride ion made hydrogen bond through N−H … F … H−N. Whereas, the intramolecular hydrogen bonding was through F−H … N in the excited state of receptor-uoride complex. Experimental absorption and emission spectra were well reproduced by the calculated vertical excitation energies. The transition state (TS) calculations were performed to understand the thermodynamic features and mechanism of host-guest interaction. The natural bond orbital analyses show the second perturbation energy for donor-acceptor interaction of Fwith hydrogen is more than 300 kcal/mol at the excited state of receptor-uoride complex, which indicates the strong single bond between uoride and hydrogen atom. The PES scan con rms that deprotonation took place at the excited state of receptor-uoride complex. The results indicate that the excited-state proton transfer (ESPT) process from N-H group nearby the anthracene moiety. The APTSC is better chemosensor than ATSC. This infer that the aromaticity will increase the e ciency of uorescence receptor towards uoride ion.