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

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• 作者：Jun Lang ; David J. Sloop ; Tien-Sung Lin
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：June 7, 2007
• 年：2007
• 卷：111
• 期：22
• 页码：4731 - 4736
• 全文大小：346K
• 年卷期：v.111,no.22(June 7, 2007)
• ISSN：1520-5215

文摘

Pulsed zero-field electron paramagnetic resonance free induction decay (ZF EPR FID) techniques are employedto study the phase transition of p-terphenyl crystals (T_c = 193 K) by measuring selectively populatedphotoexcited triplet ZF transitions of dilute pentacene molecules in p-terphenyl single crystals. The sensitivityof ZF spectroscopy to small shifts in local magnetic fields enables the studies of guest-host configurationchanges over a wide temperature range. Here we report the observation of guest pentacene (-h₁₄ and -d₁₄)triplet ZF EPR FID spectra that disappear abruptly at T_c and of spectral broadening and shift below T_c. Weinterpret these spectral changes as evidence for guest couplings to host phenyl rings. Further, these dataallow assignments of spectroscopic sites to crystallographic sites that occur in the phase transition.