Related Experiment Video
Updated: Jan 11, 2026

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
Resolving ionization-induced distortions in 2,5-difluoropyridine: influences of meta-fluorination on electronic and
Hyojung Kim1, Sung Man Park1, Chan Ho Kwon1
1Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Republic of Korea. chkwon@kangwon.ac.kr.
Abstract:
We conduct a high-resolution vacuum ultraviolet mass-analyzed threshold ionization spectroscopic study of 2,5-difluoropyridine (2,5-DFP), supported by Franck-Condon (FC) simulation and natural bond orbital analysis, to investigate the stereoelectronic influences of ortho- and meta-fluorination on ionization dynamics. The adiabatic ionization energy (AIE) is precisely determined as 77 760 ± 3 cm-1, which is lower than those of other DFP isomers owing to the reduced stabilization of the highest occupied molecular orbital (HOMO) by meta-substituted F. The mass-analyzed threshold ionization spectrum reveals well-resolved vibrational progressions and weak out-of-plane modes, indicating slight nonplanarity in the cationic D0 state. These features are successfully reproduced by FC simulations incorporating minor dihedral distortions, confirming the subtle symmetry breaking upon ionization. A second AIE of 78 227 ± 3 cm-1 is assigned to the D1 state, corresponding to ionization from a lower-lying nonbonding orbital (HOMO-1). Compared to that of 2,3-DFP, 2,5-DFP exhibits less extensive geometric reorganization upon ionization, reflecting the π-character of its singly occupied molecular orbital and its more delocalized charge distribution. These results demonstrate how meta-fluorination on the opposite side modulates the cationic geometry and frontier orbital energetics, offering fresh insights into the substitution-dependent ionization behavior of fluorinated heteroaromatics.
More Related Videos
08:54Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid
Published on: January 25, 2020
09:46Qualitative Identification of Carboxylic Acids, Boronic Acids, and Amines Using Cruciform Fluorophores
Published on: August 19, 2013
Related Concept Videos
Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene
¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
ortho–para-Directing Deactivators: Halogens
Variables Affecting Phosphorescence and Fluorescence
Molecular Shape and Polarity
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3