title: Breaking the semi-quinoid structure: spin-switching from strongly coupled singlet to polarized triplet state.
abstract: 2,7-TMPNO (4,5,9,10-tetramethoxypyrene-2,7-bis(tert-butylnitroxide)) was found to exist in semi-quinoid form with unprecedented strong intramolecular magnetic exchange interaction of 2 J/kB = 1185 K operating over a distance of 10 Å. Structural transformations with the activation energy of ΔEeq = 949 K were observed by varying the temperature, from more quinoid structure at low temperature to more biradicaloid structure at higher temperature. Moreover, this molecule undergoes a transient spin transition from singlet to polarized triplet state upon photoexcitation revealed by TREPR spectroscopy. The spin Hamiltonian parameters were determined to be S = 1, g = 2.0065, D = -0.0112 cm(-1), and E = -0.0014 cm(-1) by spectral simulation with the hybrid Eigenfield/exact diagonalization method.
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz (Germany).
authors.forename: Prince
authors.initials: P
authors.lastname: Ravat
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Teki
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ito
authors.forename: Elena
authors.initials: E
authors.lastname: Gorelik
authors.forename: Martin
authors.initials: M
authors.lastname: Baumgarten
keywords: EPR spectroscopy; density functional calculations; magnetic exchange interactions; pyrenes; semi-quinoid