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Top and side views of the pp structure (a) and side views (b)-(e) of the other isomer structures of the rotor molecule BTP-BCO. Three molecular groups are labeled in (a). (The detailed structural information and the naming method is in the supplementary material25).
(a) Calculated IR spectrum of the parallel-parallel (pp) geometry of the rotor molecule shown in (b). The red arrows in (b) indicate important vibrational displacements for three vibrational modes, at 851 cm−1 (at top), 842 cm−1 (at center), and 867 cm−1 (at bottom), seen along the long axis of the molecule. (c) shows the rotational barriers of this wheel molecule in two opposite directions: clockwise (positive angles) and anticlockwise (negative angles), starting from 0° for the pp structure shown in (b).
Snapshots of MD simulations of the parallel-parallel (pp) geometry at 450 K, at times t = 0 ps (a), 0.7 ps (b), 1.6 ps (c), and 2.5 ps (d). The direction of view is constant, perpendicular to the initial molecular plane in (a). A carbon atom is colored red to highlight the rotation of the central BCO group.
Snapshots of MD simulations of the parallel-parallel geometry at 400 K (with a constant direction of view). (a) at time t = 0 fs, (b) t = 74 fs, (c) t = 171 fs, (d) t = 237 fs, (e) t = 294 fs, (f) t = 349 fs, (g) t = 422 fs, (h) t = 497 fs, (i) t = 745 fs. One of the rotor's carbon-carbon bonds is colored yellow as reference for the rotation.
Total energy vs step from MD simulation at 400 K, (each time step is 1 fs). The arrows denoted as c, f, h, and i show four local energy minima where snapshots of the molecule are extracted for Fig. 4(c), f, h, and i, respectively. At these four points, the BCO group has undergone rotation by 30°, 60°, 90°, and 120°, respectively.
Maximum rotational angle θ and “time to stop” t until first reversal of rotation, as a function of temperature, from individual MD simulations. The calculated MD data points are connected by lines to guide the eye.
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