Fluorine position-dependent ionization dynamics and structural distortion in 2,3-difluoropyridine: a VUV-MATI and...

Area of Science:

• Organic Chemistry
• Materials Science
• Pharmaceutical Chemistry

Background:

• Pyridine derivatives possess unique electronic and structural properties vital for various scientific fields.
• Fluorine substitution modulates these properties, but the precise effects of fluorine positioning (ortho, meta) on molecular orbitals and ionization energies are not fully understood.

Purpose of the Study:

• Investigate the ionization-induced structural dynamics of 2,3-difluoropyridine (2,3-DFP).
• Clarify the influence of ortho- and meta-fluorine substitution on molecular orbitals, ionization energies, and cationic structures.
• Provide insights into the stereoelectronic effects of fluorination in heteroaromatic systems.

Main Methods:

• High-resolution vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy.
• Franck-Condon (FC) simulations for spectral analysis.
• Natural bond orbital (NBO) analysis for electronic structure elucidation.

Main Results:

• Precisely measured adiabatic ionization energy (AIE) of 2,3-DFP as 9.6958 ± 0.0004 eV.
• Observed significant geometric distortion upon ionization, with out-of-plane modes becoming FC-active.
• Proposed a second AIE of 9.7643 ± 0.0004 eV attributed to the D1 state (HOMO-1 ionization).

Conclusions:

• Fluorine substitution patterns significantly modulate valence orbital energies, cationic structures, and vibrational dynamics in pyridine derivatives.
• The study provides a detailed framework for understanding fluorination effects in heteroaromatic systems.
• Findings offer practical insights for designing functional materials and pharmaceuticals with tailored electronic properties.