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Structures and Properties of Self-Assembled Monolayers of Bistable [2]Rotaxanes on Au (111) Surfaces from Molecular Dynamics Simulations Validated with Experiment

Jang, Seung Soon and Jang, Yun Hee and Kim, Yong-Hoon and Goddard, William A., III and Flood, Amar H. and Laursen, Bo W. and Tseng, Hsian-Rong and Stoddart, J. Fraser and Jeppesen, Jan O. and Choi, Jang Wook and Steuerman, David W. and DeIonno, Erica and Heath, James R. (2005) Structures and Properties of Self-Assembled Monolayers of Bistable [2]Rotaxanes on Au (111) Surfaces from Molecular Dynamics Simulations Validated with Experiment. Journal of the American Chemical Society, 127 (5). pp. 1563-1575. ISSN 0002-7863.

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Bistable [2]rotaxanes display controllable switching properties in solution, on surfaces, and in devices. These phenomena are based on the electrochemically and electrically driven mechanical shuttling motion of the ring-shaped component, cyclobis(paraquat-p-phenylene) (CBPQT^(4+)) (denoted as the ring), between a tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene (DNP) ring system located along a dumbbell component. When the ring is encircling the TTF unit, this co-conformation of the rotaxane is the most stable and thus designated the ground-state co-conformer (GSCC), whereas the other co-conformation with the ring surrounding the DNP ring system is less favored and so designated the metastable-state co-conformer (MSCC). We report here the structure and properties of self-assembled monolayers (SAMs) of a bistable [2]rotaxane on Au (111) surfaces as a function of surface coverage based on atomistic molecular dynamics (MD) studies with a force field optimized from DFT calculations and we report several experiments that validate the predictions. On the basis of both the total energy per rotaxane and the calculated stress that is parallel to the surface, we find that the optimal packing density of the SAM corresponds to a surface coverage of 115 Å^2/molecule (one molecule per 4 × 4 grid of surface Au atoms) for both the GSCC and MSCC, and that the former is more stable than the latter by 14 kcal/mol at the optimum packing density. We find that the SAM retains hexagonal packing, except for the case at twice the optimum packing density (65 Å^2/molecule, the 3 × 3 grid). For the GSCC and MSCC, investigated at the optimum coverage, the tilt of the ring with respect to the normal is θ = 39° and 61°, respectively, while the tilt angle of the entire rotaxane is ψ = 41° and 46°, respectively. Although the tilt angle of the ring decreases with decreasing surface coverage, the tilt angle of the rotaxane has a maximum at 144 Å^2/molecule (the 4 × 5 grid/molecule) of 50° and 51° for the GSCC and MSCC, respectively. The hexafluorophosphate counterions (PF_6^-) stay localized around the ring during the 2 ns MD simulation. On the basis of the calculated density profile, we find that the thickness of the SAM is 40.5 Å at the optimum coverage for the GSCC and 40.0 Å for MSCC, and that the thicknesses become less with decreasing surface coverage. The calculated surface tension at the optimal packing density is 45 and 65 dyn/cm for the GSCC and MSCC, respectively. This difference suggests that the water contact angle for the GSCC is larger than for the MSCC, a prediction that is verified by experiments on Langmuir−Blodgett monolayers of amphiphilic [2]rotaxanes.

Item Type:Article
Related URLs:
URLURL TypeDescription
Jang, Seung Soon0000-0002-1920-421X
Jang, Yun Hee0000-0002-6604-5813
Kim, Yong-Hoon0000-0001-5209-4908
Goddard, William A., III0000-0003-0097-5716
Flood, Amar H.0000-0002-2764-9155
Laursen, Bo W.0000-0002-1120-3191
Tseng, Hsian-Rong0000-0003-0942-5905
Stoddart, J. Fraser0000-0003-3161-3697
Jeppesen, Jan O.0000-0002-3088-2994
Choi, Jang Wook0000-0001-8783-0901
Steuerman, David W.0000-0002-3464-7932
Heath, James R.0000-0001-5356-4385
Additional Information:© 2005 American Chemical Society. Received 9 September 2004. Published online 5 January 2005. Published in print 1 February 2005. The computational work was initiated with support by the National Science Foundation (NIRT, WAG). The collaboration was supported by the Microelectronics Advanced Research Corporation (MARCO, WAG and J.F.S.) and its Focus Centers on Functional Engineered NanoArchitectonics (FENA) and Materials Structures and Devices, the Moletronics Program of the Defense Advanced Research Projects Agency (DARPA, J.F.S. and J.R.H.), the Center for Nanoscale Innovation for Defense (CNID, J.F.S.), the MARCO Materials Structures and Devices Focus Center (J.R.H.). In addition, the facilities of the MSC (WAG) were supported by ONR-DURIP, ARO-DURIP, IBM (SUR), and the Beckman Institute.
Funding AgencyGrant Number
Microelectronics Advanced Research Corporation (MARCO)UNSPECIFIED
Centers on Functional Engineered NanoArchitectonics (FENA)UNSPECIFIED
Defense Advanced Research Projects Agency (DARPA)UNSPECIFIED
Office of Naval Research (ONR)UNSPECIFIED
Army Research Office (ARO)UNSPECIFIED
Caltech Beckman InstituteUNSPECIFIED
Issue or Number:5
Record Number:CaltechAUTHORS:20170420-084322252
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Official Citation:Structures and Properties of Self-Assembled Monolayers of Bistable [2]Rotaxanes on Au (111) Surfaces from Molecular Dynamics Simulations Validated with Experiment Seung Soon Jang, Yun Hee Jang, Yong-Hoon Kim, William A. Goddard III, Amar H. Flood, Bo W. Laursen, Hsian-Rong Tseng, J. Fraser Stoddart, Jan O. Jeppesen, Jang Wook Choi, David W. Steuerman, Erica DeIonno, and James R. Heath Journal of the American Chemical Society 2005 127 (5), 1563-1575 DOI: 10.1021/ja044530x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76756
Deposited By: Ruth Sustaita
Deposited On:20 Apr 2017 18:50
Last Modified:17 Nov 2020 00:01

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