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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