A model system with intramolecular hydrogen bonding: Effect of external electric field on the tautomeric conversion and electronic structures

A new model tautomeric system with intramolecular hydrogen bonding is proposed. Geometry optimizations are performed at HF and MP2 levels and absorption spectra are simulated at TDDFT level. The MP2 level of theory was chosen for studying the effect of the external electric static field (EF) on the molecular electronic structure. The geometries of the tautomers as well as the transition states are fully optimized for each magnitude and for opposite directions of the applied EF. Upon variation of the electric field strength and polarity, it is possible to stabilize different tautomeric forms of the molecule. The dipole moment, HOMO–LUMO gap and the spatial distribution of the frontier orbitals are found to be sensitive to the EF strength and polarity and the different tautomeric structures are differently affected by the field. Elongation of the conjugated system providing a large number of possible tautomeric forms is also examined at HF level. Systems similar to the studied model system have potential use in the design of new molecular electronic devices.