| Abstract
| - Thin, platelike single crystals of p-terphenyl (PT) doped with terrylene impurity molecules can be preparedby spin-coating from solution. Strikingly, individual terrylene molecules can be observed traveling inside thecrystal over distances of several micrometers by using single-molecule fluorescence imaging at roomtemperature. Analysis of the motion by single-particle tracking and correlation methods indicates that themolecules act as nanoprobes by exploring long, thin crack-like defects with correlated orientations, defectsthat can be difficult to observe by other means. Apparently, the regions accessible to the moving moleculesare in the interior of the crystal and hence are partially protected from oxidation. In addition to the travelingmolecules, which photobleach in times on the order of 32 s under continuous irradiation at 2 kW/cm2, twoother spatially fixed populations are observed: one with transition dipole oriented along the c-axis of thecrystal with a characteristic photobleaching time greater than 32 h, and one with a characteristic photobleachingtime of 18 min.
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