title: Dynamics of p-terphenyl crystals at the phase transition temperature: a zero-field EPR study of the photoexcited triplet state of pentacene in p-terphenyl crystals.
abstract: Pulsed zero-field electron paramagnetic resonance free induction decay (ZF EPR FID) techniques are employed to study the phase transition of p-terphenyl crystals (Tc = 193 K) by measuring selectively populated photoexcited triplet ZF transitions of dilute pentacene molecules in p-terphenyl single crystals. The sensitivity of ZF spectroscopy to small shifts in local magnetic fields enables the studies of guest-host configuration changes over a wide temperature range. Here we report the observation of guest pentacene (-h(14) and -d(14)) triplet ZF EPR FID spectra that disappear abruptly at Tc and of spectral broadening and shift below Tc. We interpret these spectral changes as evidence for guest couplings to host phenyl rings. Further, these data allow assignments of spectroscopic sites to crystallographic sites that occur in the phase transition.
authors.affiliation: Department of Chemistry, Washington University, St. Louis, Missouri 63130-4899, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Lang
authors.forename: David J
authors.initials: DJ
authors.lastname: Sloop
authors.forename: Tien-Sung
authors.initials: TS
authors.lastname: Lin
mesh_terms: D003460:Crystallization; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D044367:Phase Transition; D010777:Photochemistry; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013696:Temperature; D013730:Terphenyl Compounds / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D011084:Polycyclic Aromatic Hydrocarbons; D013730:Terphenyl Compounds