Switching on H-Tunneling through Conformational Control

Area of Science:

• Quantum chemistry
• Chemical physics
• Materials science

Background:

• Hydrogen tunneling (H-tunneling) is a fundamental quantum mechanical process observed across diverse scientific disciplines.
• Controlling H-tunneling for targeted chemical transformations remains a significant challenge in chemistry and materials science.

Purpose of the Study:

• To demonstrate a novel method for actively controlling H-tunneling using external radiation.
• To investigate the mechanism of radiation-induced conformational changes that facilitate H-tunneling.

Main Methods:

• Generation of a triplet 2-hydroxyphenylnitrene intermediate in a nitrogen (N₂) matrix at low temperatures (10 K) via UV irradiation of an azide precursor.
• Selective vibrational excitation at the 2ν(OH) frequency to induce conformational changes from anti- to syn-orientation of the hydroxyl (OH) moiety.
• Spectroscopic analysis and computational modeling to elucidate the H-tunneling pathway and energy landscape.

Main Results:

• External radiation successfully induced a conformational change in the 2-hydroxyphenylnitrene, bringing the hydrogen atom closer to the nitrene center.
• This conformational shift triggered spontaneous H-tunneling from the triplet nitrene to a singlet 6-imino-2,4-cyclohexadienone product.
• Computational studies confirmed that the H-tunneling proceeds via crossing of triplet-to-singlet potential energy surfaces.

Conclusions:

• The study presents a groundbreaking experimental strategy to control H-tunneling through conformational manipulation via external radiation.
• This work opens new possibilities for directing chemical reactions and manipulating molecular structures by harnessing quantum tunneling effects.