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You searched for +publisher:"University of Illinois – Urbana-Champaign" +contributor:("Martinez, Todd J."). Showing records 1 – 3 of 3 total matches.

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University of Illinois – Urbana-Champaign

1. Cremar, Lee. Insights for designing mechanochromic spiropyrans from first principles dynamics and minimum energy pathways.

Degree: PhD, 0335, 2012, University of Illinois – Urbana-Champaign

The energy needed for a chemical reaction usually comes in the form of heat or light, which may alter the arrangement of reactant molecules on the ground state or place them on an excited state to surmount an energy barrier. An alternative and less well-explored way of initiating a chemical reaction is to use an applied force to distort the reactant molecules along a specific reaction coordinate. Recent experiments have demonstrated that the nature of the applied force can have a significant effect on the distribution of reaction products. This may allow the development of novel stress-responsive materials. In this work, we use first principles dynamics and constrained optimization approaches to investigate the mechanochemical activity of a spiropyran molecule. When a particular bond is broken, the spiropyran changes color. In combination with an understanding of the specific reaction products enhanced by applied forces, this can be exploited to create a mechano-chromophore, which changes color according to the distribution of stress in a polymeric material. Our simulations explore the amount of applied force required to induce bond rupture and the specific mechanism of bond rupture for different directions and magnitude of the applied force. We use the steered molecular dynamics method in combination with “on the fly” solution of the electronic structure problem, allowing arbitrary bond rearrangement in response to the applied force. The nature of the minimal energy pathway (MEP) on the force modified potential energy surface (FMPES) was investigated and utilized to determine reaction rate expressions within the context of transition state theory. Advisors/Committee Members: Martinez, Todd J. (advisor), Martinez, Todd J. (Committee Chair), Moore, Jeffrey S. (committee member), Dlott, Dana D. (committee member), Hirata, So (committee member).

Subjects/Keywords: Mechano-chemistry; Spiropyran Mechano-chromophore; First Principles

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Cremar, L. (2012). Insights for designing mechanochromic spiropyrans from first principles dynamics and minimum energy pathways. (Doctoral Dissertation). University of Illinois – Urbana-Champaign. Retrieved from http://hdl.handle.net/2142/34565

Chicago Manual of Style (16th Edition):

Cremar, Lee. “Insights for designing mechanochromic spiropyrans from first principles dynamics and minimum energy pathways.” 2012. Doctoral Dissertation, University of Illinois – Urbana-Champaign. Accessed December 04, 2020. http://hdl.handle.net/2142/34565.

MLA Handbook (7th Edition):

Cremar, Lee. “Insights for designing mechanochromic spiropyrans from first principles dynamics and minimum energy pathways.” 2012. Web. 04 Dec 2020.

Vancouver:

Cremar L. Insights for designing mechanochromic spiropyrans from first principles dynamics and minimum energy pathways. [Internet] [Doctoral dissertation]. University of Illinois – Urbana-Champaign; 2012. [cited 2020 Dec 04]. Available from: http://hdl.handle.net/2142/34565.

Council of Science Editors:

Cremar L. Insights for designing mechanochromic spiropyrans from first principles dynamics and minimum energy pathways. [Doctoral Dissertation]. University of Illinois – Urbana-Champaign; 2012. Available from: http://hdl.handle.net/2142/34565


University of Illinois – Urbana-Champaign

2. Ong, Mitchell T. The photochemical and mechanochemical ring opening of cyclobutene from first principles.

Degree: PhD, 0335, 2010, University of Illinois – Urbana-Champaign

A textbook example of a pericyclic reaction is the electrocyclic ring opening of cyclobutene. The stereochemical outcome of this reaction can typically be predicted using the Woodward-Hoffmann rules, which are based on conservation of orbital symmetry. According to these rules, the thermal ring opening reaction will proceed in conrotatory fashion, while the photochemical ring opening reaction will proceed in disrotatory fashion. Over the years, there have been very few exceptions to the Woodward-Hoffmann rules. However, two apparent exceptions to these rules occur when the ring opening of cyclobutene is initiated by exciting the molecule with light or by applying a mechanical force. In this work, we use first principles quantum mechanics and molecular dynamics to examine the photochemical and mechanochemical ring opening of cyclobutene. We use the ab initio multiple spawning (AIMS) method in order to examine the short time dynamics of cyclobutene. We have integrated the COLUMBUS software package into AIMS, which contains analytical gradients and nonadiabatic couplings for multi-reference configuration interaction (MRCI). This provides us with a more accurate potential energy surface in which to run our dynamics on. We find that the stereochemistry for ring opening is determined on the ground state. We have also identified two S1/S0 intersections that could be relevant to the photochemical ring opening reaction. One of these intersections contains a sizable C=C torsional angle, which could explain the mixture of conrotatory and disrotatory products seen in experiment. In addition, we model the mechanical response of cyclobutene within the context of a force-modified potential energy surface (FMPES). Using this model, we perform ab initio steered molecular dynamics (AISMD) to predict possible reaction outcomes when an external force is applied. Furthermore, we locate minimum energy pathways directly on the FMPES using the nudged elastic band (NEB) algorithm. Application of an external force can bias the reaction to produce a specific product by reshaping the potential energy surface and effectively blocking off access to other competing pathways. Barrier heights and stationary point geometries along the pathways can also change as a function of the force. Finally, we apply AISMD and NEB to other new mechanophores that are currently being studied including gem-difluorocyclopropane and dicyano-cyclobutane. Both of these methods can be used to screen new mechanophores, which will aid in designing new polymeric materials that respond favorably to mechanical stress. Advisors/Committee Members: Martinez, Todd J. (advisor), Martinez, Todd J. (Committee Chair), Makri, Nancy (committee member), Lisy, James M. (committee member), Moore, Jeffrey S. (committee member).

Subjects/Keywords: Theoretical Chemistry; Cyclobutene; Mechanochemistry; Photochemistry; Woodward-Hoffmann Rules; Ab Initio Molecular Dynamics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Ong, M. T. (2010). The photochemical and mechanochemical ring opening of cyclobutene from first principles. (Doctoral Dissertation). University of Illinois – Urbana-Champaign. Retrieved from http://hdl.handle.net/2142/15509

Chicago Manual of Style (16th Edition):

Ong, Mitchell T. “The photochemical and mechanochemical ring opening of cyclobutene from first principles.” 2010. Doctoral Dissertation, University of Illinois – Urbana-Champaign. Accessed December 04, 2020. http://hdl.handle.net/2142/15509.

MLA Handbook (7th Edition):

Ong, Mitchell T. “The photochemical and mechanochemical ring opening of cyclobutene from first principles.” 2010. Web. 04 Dec 2020.

Vancouver:

Ong MT. The photochemical and mechanochemical ring opening of cyclobutene from first principles. [Internet] [Doctoral dissertation]. University of Illinois – Urbana-Champaign; 2010. [cited 2020 Dec 04]. Available from: http://hdl.handle.net/2142/15509.

Council of Science Editors:

Ong MT. The photochemical and mechanochemical ring opening of cyclobutene from first principles. [Doctoral Dissertation]. University of Illinois – Urbana-Champaign; 2010. Available from: http://hdl.handle.net/2142/15509


University of Illinois – Urbana-Champaign

3. Burkhardt, Paul. Explicit, multi-map symplectic integrator for three-body classical trajectory studies in hyperspherical coordinates.

Degree: PhD, Chemistry, 2004, University of Illinois – Urbana-Champaign

Symplectic integrators are well known for preserving the phase space volume in Hamiltonian dynamics and are particularly suited for problems that require long integration times. There is a general operator splitting method for developing explicit symplectic integration algorithms to any arbitrary even order for separable Hamiltonians where the position and momentum coordinates are uncoupled. Explicit symplectic integrators for general Hamiltonians are more difficult to obtain, but can be developed by a composition of symplectic maps if the Hamiltonian can be split into exactly integrable parts. No general technique exists for splitting any Hamiltonian of general form. Many three body problems in classical mechanics can be effectively investigated in symmetrized, hyperspherical polar coordinates, but the Hamiltonian expressed in these coordinates is non-separable. In molecular dynamics, the hyperspherical coordinates facilitate the validation and visualization of potential energy surfaces and for quantum reactive scattering problems, the coordinates eliminate the need for adjusting the wavefunction between product and reactant channels. An explicit symplectic integrator for hyperspherical coordinates has not yet been devised. This dissertation presents an explicit, multi-map symmetrized composition method symplectic integrator for three-body Hamiltonians in symmetrized, hyperspherical polar coordinates, specifically for classical trajectory studies in the plane. Advisors/Committee Members: Belford, R. Linn (Committee Chair), Martinez, Todd J. (committee member), McDonald, J. Douglas (committee member).

Subjects/Keywords: Chemistry; Symplectic integrator; Three-body classical trajectory; Hyperspherical coordinates; Classical mechanics; Hamiltonian dynamics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Burkhardt, P. (2004). Explicit, multi-map symplectic integrator for three-body classical trajectory studies in hyperspherical coordinates. (Doctoral Dissertation). University of Illinois – Urbana-Champaign. Retrieved from http://hdl.handle.net/2142/17345

Chicago Manual of Style (16th Edition):

Burkhardt, Paul. “Explicit, multi-map symplectic integrator for three-body classical trajectory studies in hyperspherical coordinates.” 2004. Doctoral Dissertation, University of Illinois – Urbana-Champaign. Accessed December 04, 2020. http://hdl.handle.net/2142/17345.

MLA Handbook (7th Edition):

Burkhardt, Paul. “Explicit, multi-map symplectic integrator for three-body classical trajectory studies in hyperspherical coordinates.” 2004. Web. 04 Dec 2020.

Vancouver:

Burkhardt P. Explicit, multi-map symplectic integrator for three-body classical trajectory studies in hyperspherical coordinates. [Internet] [Doctoral dissertation]. University of Illinois – Urbana-Champaign; 2004. [cited 2020 Dec 04]. Available from: http://hdl.handle.net/2142/17345.

Council of Science Editors:

Burkhardt P. Explicit, multi-map symplectic integrator for three-body classical trajectory studies in hyperspherical coordinates. [Doctoral Dissertation]. University of Illinois – Urbana-Champaign; 2004. Available from: http://hdl.handle.net/2142/17345

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