Spin Identification of Polyionic High-Spin Aryl-Based Heteroatomic Systems by 2D Electron Spin Transient Nutation (2D-ESTN) Spectroscopy

Molecular design, generation, and spin identification of polyionic high spins with heteroatomic π-conjugation are described. The molecular design was based upon the π-topological pseudo-degeneracy of HOMO's for high-spin polycations and LUMO's for high-spin polyanions. The pseudo-degeneracy originates in heteroatomic perturbation and high spin preference in their ground state is driven by meta- or 1,3,5-connectivity of heteroatomic sites giving rise to additive dynamic spin polarization. Polyionic high spins were generated by chemical oxidation or reduction in solution. Thus, the polyions were observed in a rigid glass solution containing reaction mixture. For such complex spin systems their reliable spin identification is essential and, therefore, we employed field-swept 2D electron spin transient nutation (2D-ESTN) spectroscopy. In this work, we have developed such a 2D-ESTN spectroscopy as deserves to enhance spectral resolution in complex spin mixture of non-oriented systems. An unequivocal and facile spin identification of the polyions was carried out, demonstrating that the topological version of the molecular design has been established for polyionic high-spin preference in heteroatomic π-conjugation. It has turned out that the 2D-ESTN spectroscopy is feasible for high spin mixture of any kinds and provides us with direct experimental discrimination between high spins of different spin multiplicities.