2D-Electron Spin Transient Nutation (2D-ESTN) Study of a Stable High- Spin Carbene (S=3)

Abstract

Stable high-spin polycarbene, polybrominated 1,3,5-tris[4-(phenylcarbeno)-phenylethy-nyl]benzene in a glass matrix was studied by Electron Spin Transient Nutation (ESTN) spectroscopy. 2D-ESTN spectra of the polycarbene were measured in order to identify a molecular spin multiplicity of the high-spin ground state. The observed nutation frequencies were assigned to those arising from the allowed ESR transitions of the septet ground state (S=3). It indicates that the high-spin state is generated by ferromagnetic interaction between stable bromo-substituted diphenylmethylenes (S=1) through a 2D topological spin coupling unit with C 3 symmetry, 1,3,5-tris(ethynyl)benzene. The observed fine-structure parameters of the septet state, D = −0.040 cm −1 and |E| = 0.007 cm −1, were well interpreted in terms of an intramolecular spin-spin interaction model. The observed small and negative D value was shown to arise from the C 3 symmetric molecular structure. The high-spin polycarbene has survived after annealing of the glass matrix. The stable triplet carbene unit is supposed to serve as a useful building block for extended super high-spin molecular systems and organic superparamagnets.