The dynamics of p-phenylene-d4 rotators in hierarchically ordered periodic mesoporous p-divinylbenzenesilica have been elucidated by deuterium solid-state NMR spectroscopy. The mesoporous material, characterized by a honeycomb lattice structure, has arrays of alternating p-divinylbenzene and siloxane layers forming the ordered walls of the mesoscopic channels. NMR expts. revealed a non-Arrhenius temp. dependence of the rotator dynamics, with rates ranging from 103 to 108 Hz between 215 K and 305 K. The regime of motion changes drastically at ∼280 K, indicating a dynamical transition with a corresponding change in heat capacity. At room temp. and above, the rotators comprise a highly mobile fluid-like rotational phase within the org. layers of the walls. However, cooling slightly below room temp. results in rigid glass-like org. layers with markedly slower dynamics. Exploiting the rotational behavior, above and below the transition, represents a means to elicit a very significant thermal response within a narrow temp. range.
Vogelsberg, C., Bracco, S., Beretta, M., Comotti, A., Sozzani, P., Garcia Garibay, M. (2012). Hypersensitive thermally-activated molecular machines: Anisotropic rotational dynamics within hierarchically ordered periodic mesoporous p-divinylbenzenesilica. In Abstracts of Papers, 243rd ACS National Meeting & Exposition, San Diego, CA, United States, March 25-29, 2012. American Chemical Society.
Hypersensitive thermally-activated molecular machines: Anisotropic rotational dynamics within hierarchically ordered periodic mesoporous p-divinylbenzenesilica
BRACCO, SILVIA;BERETTA, MARIO;COMOTTI, ANGIOLINA;SOZZANI, PIERO ERNESTO;
2012
Abstract
The dynamics of p-phenylene-d4 rotators in hierarchically ordered periodic mesoporous p-divinylbenzenesilica have been elucidated by deuterium solid-state NMR spectroscopy. The mesoporous material, characterized by a honeycomb lattice structure, has arrays of alternating p-divinylbenzene and siloxane layers forming the ordered walls of the mesoscopic channels. NMR expts. revealed a non-Arrhenius temp. dependence of the rotator dynamics, with rates ranging from 103 to 108 Hz between 215 K and 305 K. The regime of motion changes drastically at ∼280 K, indicating a dynamical transition with a corresponding change in heat capacity. At room temp. and above, the rotators comprise a highly mobile fluid-like rotational phase within the org. layers of the walls. However, cooling slightly below room temp. results in rigid glass-like org. layers with markedly slower dynamics. Exploiting the rotational behavior, above and below the transition, represents a means to elicit a very significant thermal response within a narrow temp. range.
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