Modulation of the strength of weak S-H⋯O hydrogen-bond: Spectroscopic study of the complexes of 2-flurothiophenol with methanol and ethanol.

Spectroscopic exploration of sulfur-centered hydrogen bonding involving a thiol group (S-H) as the hydrogen bond donor is scarce in the literature. Herein, we have investigated 1:1 complexes of 2-fluorothiophenol (2-FTP) with methanol (MeOH) and ethanol (EtOH) in the gas phase to examine the physical characteristics and strength of the S-H⋯O hydrogen bond. Structures, conformations, and the strength of the S-H⋯O interaction are investigated by measuring the electronic and Infrared (IR) spectra of the two complexes employing resonant two-photon ionization, UV-UV hole-burning, and IR-UV double resonance spectroscopic techniques combined with quantum chemical calculations. Three conformers of 2-FTP⋯MeOH and two conformers of 2-FTP⋯EtOH have been detected in the experiment. A comparison of the IR spectra obtained from the experiment with those of the low-energy conformers of 2-FTP⋯MeOH and 2-FTP⋯EtOH predicted from the theory confirms that all the observed conformers of the two complexes are primarily S-H⋯O hydrogen bonded. The IR red-shifts found in the S-H stretching frequencies in 2-FTP⋯MeOH and 2-FTP⋯EtOH concerning that in 2-FTP are ∼76 and ∼88 cm-1, respectively, which are much larger than that was reported earlier in the 2-FTP⋯H2O complex (30 cm-1). The strength and physical nature of different noncovalent interactions, including the S-H⋯O hydrogen bond existing in the complexes, are further analyzed using natural bond orbital analysis, quantum theory of atoms in molecules, and localized molecular orbital-energy decomposition analysis. The current investigation reveals that the S-H⋯O hydrogen bond can be strengthened by judicial choices of the hydrogen bond acceptors of higher proton affinities.

Photocatalytic α-arylation of cyclic ketones by a thermally activated delayed fluorescence molecule.

α-Arylation of cyclic ketones via an organophotocatalytic route has been described utilizing PXZ-TRZ, a molecule displaying thermally activated delayed fluorescence (TADF). Using this route, a plethora of cyclic ketones including cyclohexanone, cyclopentanone and even cyclooctanone can be effectively arylated with many aryl iodides or bromides under mild conditions.

A fluorescence based dual sensor for Zn2+ and PO43- and the application of soft computing methods to predict machine learning outcomes.

A phenolphthalein-based Schiff base, 3,3-bis-{4-hydroxy-3-[(pyridine-2-ylmethylimino)-methyl]-phenyl}-3H-isobenzofuran-1-one (PAP), has been synthesized and used for selective fluorescence 'turn on' and 'turn off' sensing of Zn2+ and PO43- respectively. The limit of detection using the 3σ method for Zn2+ is found to be 19.3 nM and that for PO43- is 8.3 µM. The sensing mechanism of PAP for Zn2+ ions has been explained by 1H NMR, 13C NMR, TRPL, ESI-MS, FT-IR, and DFT based calculations. Taking advantage of this fluorescence 'on-off' behavior of PAP in the sequential presence of Zn2+ and PO43- a two input fuzzy logic (FL) operation has been constructed. The chemosensor PAP can thus act as a metal ion and anion responsive molecular switch, and its corresponding emission intensity is used to mimic numerous FL functions. To replace various expensive, time-consuming experimental procedures, we implemented machine learning soft computing tools, such as fuzzy-logic, artificial neural networks (ANNs), and adaptive neuro-fuzzy inference systems (ANFIS), to correlate as well as predict the fluorescence intensity in the presence of any equivalent ratio of Zn2+ and PO43-. The statistical performance measures (MSE and RMSE, for example) show that the projected values of the cation and anion sensing data by the ANFIS network are the best and closer to the experimental values.