Metal‐Free γ,δ‐Unsaturated β‐Ketothiolester: Solvatochromism, AIEE and Detection of Picric Acid

Abstract

A synthesis of γ,δ‐unsaturated β‐ketothiolester depend on the properties of solvent and their relative humidity. γ,δ‐unsaturated β‐ketothiolester shows solvent dependent emission due to excited state intramolecular proton transfer (ESIPT). Increasing solvent polarity makes larger Stokes’ shifts ranging from 4072 to 6459 cm−1. γ,δ‐unsaturated β‐ketothiolester exhibit red‐shifted emission (591 nm) in the solid state than the solution. In THF‐H2O mixture, solvent polarity parameter (Δf) increases by increasing H2O ratio (0‐90%) where aggregation‐induced emission enhancement (AIEE) of γ,δ‐unsaturated β‐ketothiolester enhanced by increasing Δf. The Intermolecular interaction by polar protic solvent with γ,δ‐unsaturated β‐ketothiolester is the response for decrease in emission above 60% H2O in THF‐H2O mixture. Picric acid detection of γ,δ‐unsaturated β‐ketothiolester enhanced by AIEE with a detection limit of 2 μM. Emission quenching mechanism was identified using NMR technique. Selective detection of picric acid is high when with compared to other nitroaromatic compounds and act as a inexpensive test strip detector for picric acid.

The revelation of ESIPT behavior and fluoride response mechanism for (E)‐2‐(((1H‐benzo[d]imidazol‐2‐yl)‐imino)methyl)‐5‐(dimethylamino)‐phenol

“…Furthermore, the hydrogen bond strengthening or weakening could also be revealed based on monitoring the spectral shifts of vibrational modes involved in the formation of hydrogen bonds . The vibrational spectra of bip chromophore in the conjunct vibrational regions of the O‐H stretching mode have been shown in Figure .…”

“…Different from experimental results, the specific potential barrier of ESIPT and comprehend the mechanism of the ESIPT process can be provided based on quantum chemical computational study. And previous theoretical investigations have indicated that TDDFT/B3LYP calculated level should be efficient as far as the form of hydrogen‐transfer potential energy curves is concerned . It can provide qualitative energetic pathways for the ESIPT process of bip chromophore.…”

“…The geometric optimizations of bip , bip‐open and bip‐pt were performed using DFT in the S 0 state and using TDDFT in the S 1 state. Especially, the TDDFT method has become a very useful tool to theoretically investigate the hydrogen bonding interaction that occurs in the excited states . In addition, Becke's three‐parameter hybrid exchange functional with Lee–Yang–Parr gradient‐corrected correlation (B3LYP functional) was selected in both the DFT and TDDFT methods .…”

“…Till now, many different sensing mechanisms, such as intramolecular charge transfer (ICT), photo‐induced electron transfer (PET), fluorescence resonance energy transfer (FRET), and excited state proton transfer (ESPT) and so forth, are relevant with intra‐ or inter‐ molecular hydrogen bond. Particularly, the excited state inter‐ and intra‐ molecular proton transfer (ESIPT) reactions have been drawing great attention due to their unique photo‐physical and photo‐chemical properties.…”

“…Even though this sensor has weak fluorescence, it was reported that the anion‐binding adduct of bip is expected to be highly fluorescent based on ESIPT channel experimentally, however, the mechanism of bip in excited state is very limitted. In effect, experimental spectroscopic techniques, such as steady‐state absorption spectroscopy, fluorescence spectroscopy and time resolved fluorescence spectroscopy, just provide the indirect information about photo‐physical and photo‐chemical properties . Up to now, the theoretical investigations about the bip are very scarce in addition to the experiments.…”