Towards a better understanding of photo-excited spin alignment processes using silole diradicals

Nans Roques; Philippe Gerbier; Yoshio Teki; Sylvie Choua; Petra Lesniakovà; Jean-Pascal Sutter; Philippe Guionneau; Christian Guérin

doi:10.1039/B606593G

Towards a better understanding of photo-excited spin alignment processes using silole diradicals†

Nans Roques,^a Philippe Gerbier,*^a Yoshio Teki,*^b Sylvie Choua,^c Petra Lesniakovà,^c Jean-Pascal Sutter,^d Philippe Guionneau^e and Christian Guérin^a

Author affiliations

* Corresponding authors

^a Laboratoire de Chimie Moléculaire et Organisation du Solide-UMR-CNRS/UM2 5637, Université Montpellier II, C.C.007, Place E. Bataillon, 34095 Montpellier Cedex 5, France
E-mail: gerbier@univ-montp2.fr
Fax: +33 4 67 14 3852
Tel: +33 4 67 143 972

^b Department of Material Science, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto Sumiyoshi-ku, Osaka 558-8585, Japan
E-mail: teki@sci.osaka-cu.ac.jp
Fax: +81 6605 8585

^c Institut Charles Sadron—UPR-CNRS 22, Université Louis Pasteur, 6 Rue Boussingault, BP 40016, 67083 Strasbourg Cedex, France
E-mail: turek@ics.u-strasbg.fr
Fax: +33 3 88 414 099
Tel: +33 3 88 414 000

^d Laboratoire de Chimie de Coordination—UPR-CNRS 8241, Université Paul Sabatier, 205 route de Narbonne, 31077 Toulouse Cedex 4, France
E-mail: sutter@lcc-toulouse.fr

^e Institut de Chimie de la Matière Condensée—UPR-CNRS 9048, Université Bordeaux I, 87, Av. Dr. Schweitzer, 33608 Pessac, France
E-mail: guio@icmcb-bordeaux.cnrs.fr
Tel: +33 5 40 002 279

Abstract

The synthesis of two nitroxide-based diradicals connected to a 2,3,4,5-tetraphenylsilole (TPS) unit, especially designed to present high spin photo-excited states, is reported. While the bisnitronylnitroxide (NN) silole-based diradical, TPSNN, is unstable and experiences a spontaneous fragmentation of its imidazolinic ring into a iso-butylammomium salt, the corresponding bisiminonitroxide (IN), TPSIN, is stable both in solution and in the solid state. This diradical crystallizes in the triclinic P-1 space group with a = 10.984(1), b = 11.474(1), c = 17.492(1) Å, α = 81.10(1), β = 89.01(1), and γ = 65.71(2)°. Ground state magnetic properties of TPSIN have been investigated by means of SQUID and ESR measurements: the diradical displays weak intramolecular antiferromagnetic interactions (J/k_B ≈ −1 K), in agreement with its topology and with the molecular packing observed in its crystal structure. In order to investigate the magnetic photo-excited states of TPSIN, time-resolved ESR experiments (TRESR) have been performed on this radical species. Despite the presence of both an appropriate topology for the diradical and a triplet photo-excited state for the TPS coupler, no TRESR signal was observed for this molecule within the timescale of the measurement. In addition to the work already published in this field, this result clearly indicates that besides the radical nature, the π-topological requirements and the need of photo-tunable spin-states for the coupler, the flexibility of the molecule also plays a crucial role in the achievement of photo-induced spin alignment processes.

New Journal of Chemistry

Towards a better understanding of photo-excited spin alignment processes using silole diradicals†

Abstract

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