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URL:https://murmitoyen.com/events/vanille/udem/detail/374324
LOCATION:Université de Montréal - Pavillon J.-Armand-Bombardier\, 5155\, 
 chemin de la rampe \, Montréal\, QC\, Canada\, H3T 2B2
SUMMARY:Radicals as Functional Materials: Ferromagnets\, Photomagnets and M
 etals –  Richard T. Oakley\, Waterloo
DESCRIPTION:Richard T. Oakley\, FRSC\, Professor of Chemistry\, Department
  of Chemistry\, University of Waterloo\, Waterloo\, Ontario\, N2L 3G1\, Ca
 nada.In principle\, the unpaired electron furnished by a molecular radical
  should be capable of serving as a carrier of charge [1]. The problem with
  this idea lies in the fact that there is an intrinsically high Coulombic 
 barrier U to charge transfer associated with any system possessing a half-
 filled band (f = ½) electronic structure. As a result organic radicals ar
 e Mott insulators. Overcoming the charge repulsion barrier requires that i
 ntermolecular hopping interactions (t)\, and hence the electronic bandwidt
 h W\, be sufficiently large to offset U. When W > U\, the Mott-Hubbard gap
  ΔE should vanish\, and a metallic state prevail.Our approach to realizin
 g such a system has focused on the use sulfur and selenium based heterocyc
 lic radicals. The combination of heavy (soft) heteroatoms and a highly del
 ocalized spin distribution decreases U\, while the enhanced intermolecular
  interactions afforded by the spatially extensive 3p/4p valence orbitals o
 f S/Se increases t and W. This chemical control\, coupled with the aid of 
 physical pressure to amplify W\, has produced the first organic radical me
 tals [2]. We have also demonstrated that heavy atom radicals are effective
  in the design of organic ferromagnets [3]\, and that the accompanying spi
 n-orbit effects give rise to magnetic anisotropies normally associated wit
 h d-block metals [4].Traditionally\, the downside of using heavy atom radi
 cals as functional materials has been their tendency dimerize to a CDW sta
 te\, a transformation which quenches spin and charge carriers. Recently\, 
 however\, we have demonstrated the photoinduced dissociation of radical di
 mers (S = 0) to afford long lived metastable radical states (S = ½). Thes
 e materials offer appealing opportunities for the development of metal-fre
 e photomagnetic switching devices [5].In this presentation I will summariz
 e recent work in these three related areas\, that is\, the use of neutral 
 radicals in the design of organic (i) magnetic\, (ii) photomagnetic and (i
 ii) conductive materials. References:[1] N. H. McCoy and W. C. Moore\, J.
  Am. Chem. Soc. 33\, 273 (1911).[2] J. W. L. Wong\, A. Mailman\, K. Lekin\
 , S. M. Winter\, W. Yong\, J. Zhao\, S. V. Garimella\, J. S. Tse\, R. A. S
 ecco\, S. Desgreniers\, Y. Ohishi\, F. Borondics and R. T. Oakley\, J. Am.
  Chem. Soc. 136\, 1070(2014).[3] C. M. Robertson\, A. A. Leitch\, K. Cvrka
 lj\, R. W. Reed\, D. J. T. Myles\, P. A. Dube and R. T. Oakley\, J. Am. Ch
 em. Soc. 130\, 8414 (2008). [4] S. M. Winter\, R. T. Oakley\, A. E. Koval
 ev and S. Hill\, Phys. Rev. B. 85\, 094430 (2012).[5] H. Phan\, K. Lekin\,
  S. M. Winter\, R. T. Oakley and M. Shatruk\, J. Am. Chem. Soc. 135\, 1567
 4 (2013). Site web du groupe du  Prof. OakleyCette conférence est prés
 entée par le RQMP Versant Nord du Département de physique de l'Universi
 té de Montréal et le Département de génie physique de Polytechnique Mo
 ntréal.
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