Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7901635 | Journal of Non-Crystalline Solids | 2015 | 9 Pages |
Abstract
The rotational dynamics of tetracene and rubrene in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([C4C1im][PF6]) at the glass transition (Tg = 196 K), from Tg â 6 K to Tg + 4 K, were measured using the technique of fluorescence recovery after photobleaching. The rotational anisotropy decays of these probes in [C4C1im][PF6] were found to be non-exponential and well fit by the Kohlrausch-Williams-Watts (KWW) function with the stretching parameter βKWW equal to 0.70 ± 0.03 for tetracene and 0.88 ± 0.04 for rubrene in the temperature range of the measurements. The rotational correlation time Ïc at Tg is equal to 19 ± 1 s for the smaller probe tetracene and 180 ± 40 s for the larger probe rubrene. Below Tg, Ïc shows a slight decoupling from the extrapolation of fits of the Vogel-Fulcher-Tammann equation to the viscosity η. This decoupling is characterized by a fractional Debye-Stokes-Einstein relation, Ïc â ηξ/T, with ξ equal to 0.78 ± 0.02 for rubrene and 0.85 ± 0.01 for tetracene. The dependence of βKWW on probe size is consistent with the dynamics in [C4C1im][PF6] being heterogeneous and is rationalized in terms of the time scale of the probe rotational motion compared to the domain exchange time.
Related Topics
Physical Sciences and Engineering
Materials Science
Ceramics and Composites
Authors
Fehmi Bardak, Justin R. Rajian, Pillhun Son, Edward L. Quitevis,