An anti-quinoid structure in dual fluorescence of fluozazene molecule and solvent effect of intramolecular charge transfer

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

The mechanism of host-guest interaction of receptors towards fluoride 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-fluoride complex, the added fluoride 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-fluoride 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 that the second perturbation energy for donor-acceptor interaction of F^- with hydrogen is more than 300 kcal/mol^-1 at the excited state of receptor-fluoride complex, which indicates the strong single bond between fluoride and hydrogen atom. The PES scan confirms that deprotonation took place at the excited state of receptor-fluoride complex. The results indicate the excited-state proton transfer (ESPT) process from N-H group nearby the anthracene moiety. The APTSC is a better chemosensor than ATSC. This infers that the aromaticity will increase the efficiency of fluorescence receptor towards fluoride ion. A schematic representation of sensing mode of anthracene-based thiosemicarbazones toward fluoride ion. The fluoride ion first makes a hydrogen bond with NH proton nearby anthracene moiety. The excited state proton transfer mechanism was confirmed by PES and NBO studies.

Deactivation mechanism of a novel AIE-active naphthalimide derivative in more polar solutions

We used experimental and computational methods to unveil the deactivation mechanism of a new AIE-active naphthalimide derivative in polar solutions.

A THEORETICAL STUDY ON DUAL FLUORESCENCE OF 4-DIMETHYLAMINOPYRIDINE BY POLARIZABLE CONTINUUM MODEL

Dual fluorescence spectra of 4-dimethylaminopyridine (DMAP) is investigated using time-dependent density functional theory and complete active space self-consistent field methods. Electronic absorption and emission spectra of DMAP have been investigated in three solvents, that is, cyclohexane, chloroform, and acetonitrile. The present study reveals that the dual fluorescence phenomena of DMAP appear in the cases of acetonitrile and chloroform, but not in cyclohexane. The electronic structures of the ground state and the intramolecular charge transfer states are, therefore, studied in order to reveal the insight of dual fluorescence. Our theoretical results suggest that the twisting of dimethylamino moiety in DMAP is necessary for the intramolecular charge transfer. The mechanism of the dual fluorescence of DMAP is discussed based on the twisted intramolecular charge transfer model and the dual fluorescence phenomenon is explained theoretically.

Dual Fluorescence of Fluorazene in Solution: A Computational Study

The fluorazene molecule presents dual fluorescence in polar solvents. Its absorption and emission properties in gas phase and in acetonitrile solution have been studied theoretically using the complete active space second-order perturbation//complete active space self-consistent field quantum methodology and average solvent electrostatic potential from molecular dynamics for the solvent effects. In gas phase, two optimized excited-state geometries were obtained, one of them corresponds to a local excitation (LE), and the other is an intramolecular charge transfer (ICT) and lies higher in energy. In acetonitrile solution, a second ICT structure where the molecule remains planar is found, and the energy differences are reduced. Fluorescence energies from LE and the planar ICT have a good agreement with the experimental bands, but emission from the bent ICT has too low an energy.