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.

S-H···O Hydrogen Bond Can Win over O-H···S Hydrogen Bond: Gas-Phase Spectroscopy of 2-Fluorothiophenol···HO Complex.

Study of sulfur (S) centered hydrogen bonding (SCHB) interactions in the literature is mostly limited to the molecular systems where S acts as a hydrogen-bond acceptor. It has been found that this unconventional SCHB is similar in strength to any conventional hydrogen bonding interaction involving electronegative atoms. However, SCHB involving S as a hydrogen-bond donor is not explored much in the literature.

Observation of an Unusually Large IR Red-Shift in an Unconventional S-H···S Hydrogen-Bond.

The S-H···S non-covalent interaction is generally known as an extremely unconventional weak hydrogen-bond in the literature. The present gas-phase spectroscopic investigation shows that the S-H···S hydrogen-bond can be as strong as any conventional hydrogen-bond in terms of the IR red-shift in the stretching frequency of the hydrogen-bond donor group. Herein, the strength of the S-H···S hydrogen-bond has been determined by measuring the red-shift (∼150 cm) of the S-H stretching frequency in a model complex of 2-chlorothiophenol and dimethyl sulfide using isolated gas-phase IR spectroscopy coupled with quantum chemistry calculations.

A Sandwich Azobenzene-Diamide Dimer for Photoregulated Chloride Transport.

There has been a tremendous evolution for artificial ion transport systems, especially gated synthetic systems, which closely mimic their natural congeners. Herein, we demonstrate a trans-azobenzene-based photoregulatory anionophoric system that transports chloride by forming a sandwich dimeric complex. Further studies confirmed a carrier-mediated chloride-anion antiport mechanism, and the supramolecular interactions involved in chloride recognition within the sandwich complex were revealed from theoretical studies.