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On the Energetics of Conformational Switching of Molecules at and Close to Room Temperature
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posted on 2014-01-29, 00:00 authored by Stefanie Ditze, Michael Stark, Florian Buchner, André Aichert, Norbert Jux, Nicola Luckas, Andreas Görling, Wolfgang Hieringer, Joachim Hornegger, Hans-Peter Steinrück, Hubertus MarbachWe observe and induce conformational
switching of individual molecules
via scanning tunneling microscopy (STM) at and close to room temperature.
2H-5,10,15,20-Tetrakis-(3,5-di-tert-butyl)-phenylporphyrin
adsorbed on Cu(111) forms a peculiar supramolecular ordered phase
in which the molecules arrange in alternating rows, with two distinct
appearances in STM which are assigned to concave and convex intramolecular
conformations. Around room temperature, frequent bidirectional conformational
switching of individual molecules from concave to convex and vice versa is observed. From the temperature dependence,
detailed insights into the energy barriers and entropic contributions
of the switching processes are deduced. At 200 K, controlled STM tip-induced
unidirectional switching is possible, yielding an information storage
density of 4.9 × 1013 bit/inch2. With this
contribution we demonstrate that controlled switching of individual
molecules at comparably high temperatures is possible and that entropic
effects can be a decisive factor in potential molecular devices at
these temperatures.