Muonium avoided level crossing measurement of electron spin relaxation rate in a series of substituted anthradithiophene based molecules

• The electron spin relaxation rate (eSR) on three anthradithiophenes was measured.
• The anthradithiophene molecules are identical apart from replaced side group atoms.
• The eSR is independent of the increasing atomic number, Z, of the replaced atoms.
• The results are compatible with previous reports, where the eSR increases with Z.
• The electron wavefunction is strongly localised on the backbone of the molecules.

Muon spin spectroscopy and in particular the avoided level crossing technique is introduced, with the aim of showing it as a very sensitive local probe for electron spin relaxation in organic semiconductors. Avoided level crossing data on tert-butyl-ethynyl anthradithiophene, tri-methyl-silyl-ethynyl anthradithiophene and tri-ethygermyl-ethynyl anthradithiophene at different temperatures are presented. This series of molecules have an identical anthradithiophene backbone, but we have performed a targeted substitution on the central atom of the two side groups, of C, Si and Ge. We extracted the electron spin relaxation for the three molecules of this series and discuss them in the context of previously published results.

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