Difluorodiazirine (CF2N2): a quantum mechanical study of the electron density and of the electrostatic potential in the ground and excited electronic states

Author(s)

Terrabuio, Luiz Alberto ^{[1, 2]} ; Andrade Haiduke, Roberto Luiz ^[2] ; Matta, Cherif F. ^{[3, 1, 4]}

Affiliation

^[1] Mt St Vincent Univ, Dept Chem & Phys, Halifax, NS B3M 2J6 - Canada

^[2] Univ Sao Paulo, Dept Quim & Fis Mol, Inst Quim Sao Carlos, Ave Trabalhador Sao Carlense, 400 CP 780, BR-13560970 Sao Carlos, SP - Brazil

^[3] Dalhousie Univ, Dept Chem, Halifax, NS B3H 4J3 - Canada

^[4] St Marys Univ, Dept Chem, Halifax, NS B3H 3C3 - Canada

• Document type: Journal article
• Source: THEORETICAL CHEMISTRY ACCOUNTS; v. 135, n. 3 FEB 24 2016.
• Web of Science Citations: 4

Abstract

The difluorocarbene radical (:CF2), used in organic synthesis and in photoaffinity labeling, can be generated by the pyrolytic or photolytic decomposition of 3,3-difluorodiazirine (CF2N2, DFD). DFD possesses no dipole moment in the ground electronic state S-0 but has an experimental dipole of 1.5 +/- 0.2 debye (D) in its first singlet excited state S-1. These observations have been ascribed to the shift in electron population between orbitals (Frenking et al. in J Comp Chem 28: 117-126, 2007). An alternative real-space explanation is presented, which shows that the vanishing dipole moment in S-0 results from a balance between a charge transfer contribution due to the flow of charge between atoms and an atomic polarization term due to the non-sphericity of atoms in molecules. This balance is altered in S-1. This orbital-free description is shown to be consistent with an incipient dissociation of DFD to :CF2 and N-2 upon excitation. The Laplacian of the electron density and the molecular electrostatic potential exhibit significant reorganization on excitation, mirroring one another, with consequential changes in chemical reactivity. Conforming to Hund's rule, the lowest excited state is a triplet state (T-1), and the next level, the one examined in this work, is the first singlet excited state (S-1) with vertical excitation energies of 2.81 and 3.99 eV, respectively. The calculated dipole moment magnitudes (in D) are 0.05 (S-0), 0.973 (T-1), and 0.969 (S-1) all pointing their negative end toward the nitrogens. The maximal average lifetime of S-1 (in absence of non-radiative de- excitation) is ca. 30 ps, sufficient for its slowest vibrational normal mode to complete 400 oscillations. From a comparison of Hartree-Fock, MP2, QCISD, CCSD, and TD-DFT/B3LYP calculations with experiment (all using an aug-cc-pVTZ basis set), for both the ground and excited states of DFD, the method of choice appears to be QCISD, the one used in this work. (AU)

• FAPESP's process: 10/18743-1 - Employment of multipoles from the quantum theory of atoms in molecules and kinetic studies in systems found in the interstellar medium
• Grantee: Roberto Luiz Andrade Haiduke
• Support Opportunities: Regular Research Grants
• FAPESP's process: 14/23714-1 - Electronic structure relativistic calculations for evaluation of new prolapse-free basis sets
• Grantee: Roberto Luiz Andrade Haiduke
• Support Opportunities: Regular Research Grants