Noncovalent interactions in the gas phase: the anisole-phenol complex

Area of Science:

• Molecular Spectroscopy
• Quantum Chemistry
• Supramolecular Chemistry

Background:

• Understanding non-covalent interactions is crucial for molecular recognition and materials science.
• The anisole-phenol complex serves as a model system for studying hydrogen bonding and π-π interactions.

Purpose of the Study:

• To elucidate the equilibrium structures of the anisole-phenol complex in its ground (S0) and first excited (S1) electronic states.
• To investigate the nature and strength of intermolecular interactions, including hydrogen bonding and π-π interactions, within the complex.
• To determine the origin of the electronic transitions and their localization within the complex.

Main Methods:

• Resonance-enhanced multiphoton ionization (REMPI) spectroscopy.
• High-resolution laser-induced fluorescence (HR-LIF) spectroscopy.
• Density functional theory (DFT) computations (TD-M05-2X/M05-2X//N07D).
• First-principle spectra simulations.

Main Results:

• The band origin of the S(1) ← S(0) electronic transition was successfully located and assigned to a transition localized on the phenol moiety.
• The equilibrium structures of the anisole-phenol complex in both S0 and S1 states were determined.
• A stable nonplanar structure stabilized by a hydrogen bond (phenol as donor, anisole oxygen as acceptor) and a secondary interaction (anisole methyl hydrogens with phenol π-system) was identified.

Conclusions:

• The combined spectroscopic and computational approach provides a comprehensive understanding of the anisole-phenol complex.
• The identified intermolecular interactions dictate the complex's structure and influence its photophysical properties.
• Further studies on potential energy surfaces offer insights into the system's photodynamics.