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Updated: Dec 14, 2025
Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
Geometry of Structurally Non-Rigid Pyridinium Cations in an Excited State
Vladimir Kharlanov1, Vladislav Papper2
1Institute of Chemistry, Humboldt University of Berlin, Brook-Taylor-Str. 2, 12489, Berlin, Germany.
Abstract:
Quantum-chemical calculations of phenyl-substituted pyridinium cations established the formation of two non-rigid equilibrium structures in a singlet excited S1 state. These two structures are characterized by a significant torsion of the methyl group and flattened geometry of the phenyl rings relative to the plane of the heteroaromatic ring, as well as sp3 hybridization of a nitrogen atom. Structural features of the S1 equilibrium structures and their deviation from the pyridinium cation geometry in the ground state explain the experimentally detected abnormally large Stokes shift.
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