Research paperDifluorodiazirine (CF2N2): A comparative quantum mechanical study of the first triplet and first singlet excited states

- 3,3′-Difluorodiazirine possesses a dipole moment in its first two excited states (T1 and S1).
- The dipole moments of the T1 and S1 states are equal but originate from different atomic polarization and charge transfer terms.
- Electron localization-delocalization matrices (LDMs) capture the electronic structure of the ground and excited states.

3,3′-Difluorodiazirine is a precursor of difluorocarbene radical (:CF2) which is used in organic synthesis and photo affinity labelling. This molecule possesses no dipole moment in the ground electronic state (S0) but has a significant dipole moment (of magnitude ~0.97 D) in both its first (triplet, T1) and second (singlet S1) excited states. These equal dipole moments are shown to originate from widely differing atomic polarization and inter-atomic charge transfer terms (defined by the Quantum Theory of Atoms in Molecules (QTAIM)). The calculated vertical/adiabatic excitation energies for the T1 and S1 states are 2.81/2.63 and 3.99/3.78 eV, respectively. Geometries, vibrational frequencies, atomic charges and spin populations, and the localization-delocalization matrices (LDMs) (Matta, J. Comput. Chem. 35 (2014) 1165) of the excited states are compared with those of the ground state. All calculations have been conducted at the (U)QCISD/aug-cc-pVTZ level of theory.

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