title: Muoniated spin probes in the discotic liquid crystal HHTT: rapid electron spin relaxation in the hexagonal columnar and isotropic phases.
abstract: Avoided level crossing muon spin resonance (ALC-μSR) spectroscopy was used to study radicals produced by the addition of the light hydrogen isotope muonium (Mu) to the discotic liquid crystal (DLC) 2,3,6,7,10,11-hexahexylthiotriphenylene (HHTT). Mu adds to the secondary carbon atoms of HHTT to produce a substituted cyclohexadienyl radical, whose identity was confirmed by comparing the measured hyperfine coupling constants with values obtained from DFT calculations. ALC-μSR spectra were obtained in the isotropic (I), hexagonal columnar (Col(h)), helical (H), and crystalline (Cr) phases. In the I and Col(h) phases the radicals, which are incorporated within the stacks of HHTT molecules as isolated paramagnetic defects, undergo extremely rapid electron spin relaxation, on the order of a hundredfold faster than in the H or Cr phases. The electron spin relaxation rate increases significantly with increasing temperature and appears to be caused by the liquidlike motion within the columns, which modulates the overlap between the π system of the radical and the π systems of the neighboring HHTT molecules, and hence, the hyperfine coupling constants. Rapid electron spin relaxation should occur for any π radical incorporated within the columns of a DLC, which may limit the utility of DLCs for future spin-based technologies.
authors: Centre for Molecular and Materials Science, TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, Canada, V6T 2A3. iain.mckenzie@triumf.ca
authors: Iain
authors: I
authors: McKenzie
authors: Andrew N
authors: AN
authors: Cammidge
authors: Hemant
authors: H
authors: Gopee
authors: Herbert
authors: H
authors: Dilger
authors: Robert
authors: R
authors: Scheuermann
authors: Alexey
authors: A
authors: Stoykov
authors: Upali A
authors: UA
authors: Jayasooriya
mesh_terms: D016880:Anisotropy; D003198:Computer Simulation; D004579:Electron Transport; D050866:Liquid Crystals / Q000737:chemistry*; D008651:Mesons; D008956:Models, Chemical; D008958:Models, Molecular; D044367:Phase Transition; D013113:Spin Labels
chemical_list: D013113:Spin Labels