Solvent Control of the Soft Angular Potential in Hydroxyl−π Hydrogen Bonds: Inertial Orientational Dynamics

Abstract

Ultrafast polarization and wavelength selective IR pump-probe spectroscopy is used to measure the inertial and long time orientational dynamics of π-hydrogen bonding complexes. Inertial orientational relaxation is sensitive to the angular potential associated with the hydrogen bond. The complexes studied are composed of phenol-OD (hydroxyl hydrogen replaced by deuterium) and various π-base solvents with different electron donating or withdrawing substituents (chlorobenzene, bromobenzene, benzene, toluene, p-xylene, mesitylene, 1-pentyne). The different substituents provide experimental control of the hydrogen bond strength. The inertial orientational relaxation of the complexes, measured at the center frequency of each line, is independent of the hydrogen bond strength, demonstrating the insensitivity of the OD inertial dynamics, and therefore the H-bond angular potential, to the hydrogen bond strength. OD stretch absorption bands are inhomogeneously broadened through interactions with the solvent. The hydrogen bonding complexes all have similar wavelength dependent inertial orientational relaxation across their inhomogeneously broadened OD stretch absorption lines. The wavelength dependence of the inertial reorientation across each line arises because of a correlation between local solvent structure and the angular potential. These two results imply that local solvent structure acts as the controlling influence in determining the extent of inertial orientational relaxation, and therefore the angular potential, and that variation in the π-hydrogen bond strength is of secondary importance.

An analysis of the role of nonreactive plasticizers in the crosslinking reactions of a rigid resin

“…There are three types of intermolecular interactions in the phenolic resin, π–π interaction, π–OH interaction and most prevalent, hydrogen bonded hydroxyl groups that stabilize its structure . Methyl benzoate has the physical features that can potentially disrupt all three types of intermolecular interactions.…”

“…Methyl benzoate (MB) is such an example. Its positively charged delocalized aromatic structure and polar ester group can disrupt three types of intermolecular interactions in the phenolic resin namely ‐OH – ‐OH hydrogen bonding, OH–π hydrogen bonding and π–π ring–ring interaction . Because of its size, it also offers an increase in entropic contribution to facilitate the plasticization effect.…”

Mode-specific intermolecular vibrational energy transfer. II. Deuterated water and potassium selenocyanate mixture

“…The slow rotational decay time constant ͑Ͼ1 ps͒ is independent of the inertial decay amplitude. 50,51 The second is the nature of the narrowpump/broad-probe scheme of our experiments, a significant portion of the inertial signal from time zero is from delays of 200-300 fs. The two possible reasons ͑especially the ultrafast inertial decay͒ can make the structure determined by Eq.…”

“…The first one is a possible ultrafast inertial rotational decay component ͑within 200 fs͒, whose amplitude is dependent on the angular potential of the molecule. 50,51 The ultrafast inertial rotational decay component is frequency dependent. The slow rotational decay time constant ͑Ͼ1 ps͒ is independent of the inertial decay amplitude.…”

Hydrogen Bond Migration between Molecular Sites Observed with Ultrafast 2D IR Chemical Exchange Spectroscopy

“…Deuterated phenol was prepared by methods outlined previously 36. All other chemicals were used as obtained from Sigma-Aldrich.…”