Contributed talk

Hyperfine insights into the electronic structure of paramagnetic nanographene systems
Gabriel Moise¹, S. Fernández², M. Vaganov¹, F. García², D. Peña², and A. Ardavan¹

1 The Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, United Kingdom, OX1 3PU
2 Centro Singular de Investigacíon en Química Biolóxica y Materias Moleculares, C/ Jenaro de la Fuente s/n (esquina Avda. Mestre Mateo), Campus Vida, Universidade de Santiago de Compostela, Santiago de Compostela, Spain, 15782

The design of nanographene based spintronic devices requires research into methods of injecting electron spin density, methods of controlling spin delocalisation and spin polarisation, and methods for coherent manipulation of the spins. Understanding these aspects is therefore reliant on experiments which probe the finest, and hyperfinest, details of the electronic structure of paramagnetic nanographenes. In this contribution, we characterise the magnetic properties of a variety of nanographenes by employing the complete suite of continuous wave and pulse Electron Spin Resonance (ESR) techniques. These experiments are used to obtain accurate measurements of the hyperfine interactions between the electrons and the spin active nuclei of the system. The measured hyperfine landscape is then reconciled with quantum chemical calculations to yield a full description of the spin Hamiltonian of the system.

One of the molecules explored in this work is the F-AA-F diradical system (depicted above) which is prepared by reduction of the diol precursor with stannous chloride. This diradical has been a central theme of research for many of the members of the SPRING consortium and beyond [1,2]. In this particular contribution, we shed light on the rich properties and behaviours of F-AA-F in liquid and frozen solutions. It will transpire that the nuclear spins present in the system are sensitive witnesses of the electronic spin state of the various inter-molecular structures present in solution. Considering this finding, we also explore the feasibility of coherent electron-nuclear spin manipulation techniques on the F-AA-F system and other analogous systems.

[1] Dong S., Li Z. (2022) Recent progress in open-shell organic conjugated materials and their aggregated states. J. Mater. Chem. C, 10:2431-2449.
[2] Zeng Z., et al. (2012) Stable tetrabenzo Chichibabin’s hydrocarbons: tunable ground state and unusual transition between their closed-shell and open-shell resonance forms. J. Am. Chem. Soc., 134(35):14513-14525.