Influence of the aliphatic chain on the (hydrogen-bonded) p-aminobenzonitrile complexes with methanol and ethanol

Theoretical Understanding of the Nonlinear Raman Shift of C≡N Stretching Vibration of p-Aminobenzonitrile in Supercritical Water

Subcritical and supercritical fluids (SCF) have attracted significant attention in the past few decades because of their unique properties. In a previous study, a nonlinear Raman shift of the C≡N stretching vibration of p-aminobenzonitrile (p-ABN) with respect to the supercritical water (SCW) density was observed [K. Osawa et al., J. Phys. Chem. A 2009, 113, 3143-3154]. Although a plausible mechanism of the nonlinear Raman shift was proposed in the study, the discussion at the atomistic level was inadequate. To elucidate the nonlinear Raman shift mechanism of the C≡N stretching vibration of p-ABN in SCW from a theoretical viewpoint, we employed RISM-SCF-cSED, which is the hybrid method between quantum mechanics and statistical mechanics. We discovered that the hydrogen-bonding effect is dominant at low- and middle-density regions, while the packing effect is dominant at the high-density region. The balances of these effects determine the Raman shift of p-ABN in SCF.

Mass resolved IR spectroscopy of aniline–water aggregates

Aniline is the simplest aromatic amine and therefore it is a prototypical system to study the microhydration and excited state dynamics of aromatic amines.

Single water solvation dynamics in the 4-aminobenzonitrile–water cluster cation revealed by picosecond time-resolved infrared spectroscopy

The excess energy of photoionization can control the time scale of single water solvent orientation dynamics from picoseconds to infinitely long trapping in a local minimum.

Nuclear quadrupole coupling constants of two chemically distinct nitrogen atoms in 4-aminobenzonitrile

The rotational spectrum of 4-aminobenzonitrile in the gas phase between 2 and 8.5 GHz is reported. Due to the two chemically distinct nitrogen atoms, the observed transitions showed a rich hyperfine structure. From the determination of the nuclear quadrupole coupling constants, information about the electronic environment of these atoms could be inferred. The results are compared to data for related molecules, especially with respect to the absence of dual fluorescence in 4-aminobenzonitrile. In addition, the two-photon ionization spectrum of this molecule was recorded using a time-of-flight mass spectrometer integrated into the setup. This new experimental apparatus is presented here for the first time.

Molecular hydration of propofol dimers in supersonic expansions: formation of active centre-like structures

Solvation of propofol dimers is characterized by the formation of hydrogen bond networks attached to an active site-like centre.

Efficient singlet-state deactivation of cyano-substituted indolines in protic solvents via CN--HO hydrogen bonds

The photophysical properties of indoline (I) and three of its derivatives, namely, N-methylindoline (MI), 5-cyanoindoline (CI), and 5-cyano-N-methylindoline (CMI), are studied in H-donating solvents of varying polarity. Based on measurements of fluorescence yield and lifetime, and of triplet yield and hydrated-electron formation, two distinct mechanisms of solvent-induced fluorescence quenching are evidenced. The first mechanism involves the cyano substituent and leads to an increase in the rate constant of internal conversion of one order of magnitude in ethanolic solution and of more than two orders of magnitude in water, as compared to solutions in n-hexane or acetonitrile. A similar trend had previously been observed in the case of 4-N,N-dimethylaminobenzonitrile (DMABN). The second mechanism reduces the fluorescence lifetimes of the non-cyanated derivatives in aqueous solution by one order of magnitude and is related to the formation of hydrated electrons. Neither of these mechanisms is influenced by methylation at the ring nitrogen. Quantum chemical calculations are performed on the ground and excited states of the hydrogen-bonded complexes between protic solvents and MI as well as CMI. Stable hydrogen-bonded configurations involving the CN substituent and a solvent OH group are found; these configurations are stable both in the ground and the first excited singlet states, whereas the corresponding complex at the ring amino nitrogen is stable in the ground state only. The CN--HO configuration is therefore a prime candidate for a mechanistic explanation of the observed quenching by the first mechanism. These findings may have useful applications for the design of fluorescence probes for water in biological systems.